A Smell Primer

C H A P T E R

5 A Smell Primer

PHOTO: Lemon Zest. r 2019 Grace Natoli Sheldon. Reprinted with permission.

Pearl of Wisdom: My sense of taste is fine, but I am just over 60 years of age. I enjoy what I eat and drink.

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O U T L I N E Summary

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Introduction

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The Sense of Smell (Olfaction) The Olfactory System Emotion Memory Habituation Motivation

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Aging, Nutrition and Taste. DOI: https://doi.org/10.1016/B978-0-12-813527-3.00005-3

Cognition (Conscious Thoughts) How Smells Are Perceived Expectations Interpretations Evolutions Genes Infants Pregnancy Adulthood

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© 2019 Elsevier Inc. All rights reserved.

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Types of Aromas Aroma Categorizations Multidimensional Aroma Classifications

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Aromas and Aging

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Smell and Behavior

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Pheromones

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Smell and Health

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Smell and Obesity

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Smell and Weight Loss

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Smell Disorders: Mechanical and Metabolic Types of Smell Disorders Diagnosis of Smell Impairment Smell Tests to Detect Olfactory Function Treatments for Smell Disorders Smell Fatigue

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Smell Adaptations Improving the Sense of Smell Utilizing Smell Memory for Improving Smell Sensations

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Interactions of the Sense of Smell with Other Senses Sight Sound Taste Touch

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Challenging Assumptions About Chemosensory Changes with Aging

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Digest

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Manner of Speaking

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References

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LEARNING OBJECTIVES 1. Describe the sense of smell and its passageways, and how the sense of smell may be affected by the physiological changes that are associated with aging. 2. Differentiate the sense of smell from the sense of taste and its interaction with flavor, and indicate how each of these senses transforms independently and collectively throughout the aging process. 3. Recognize the vital significance of smell disorders, and note their potential effects upon health and disease, in addition to taste, flavor and enjoyment. 4. Indicate how the sense of smell interacts with the senses of sight, sound and touch to affect the sense of taste, and identify these impacts on aging. 5. Associate smell decline with aging, disease and health, and align age-appropriate improvements.

SUMMARY To fully examine the sense of smell, how the sense of smell interacts with the sense of taste, and what may be done to compensate for the probable loss of smell in the aging.

INTRODUCTION The sense of smell is referred to as the chemoreception olfaction. Olfaction is one of the oldest senses and one of the most important senses for interacting with the environment. Olfaction is critical for health and well-being; specifically for the capacity to identify aromas that are hazardous, nourishing, sexually satisfying and/or memorable. In humans, the sense of smell has important interconnections with language and neuro-vegetative areas (necessary to maintain life), and plays an important role in the identification of objects and in the modulation of behavior and interpersonal relationships. The sense of smell is able to accomplish these many functions because there are thousands of different smells and smell variations [1].

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Olfaction may be a person’s first response to stimuli, such as environmental poisons, fire or rotted food. Long before a person sees a food or beverage or tastes their nuances they may be able to detect their odors. As few as one molecule in a million may be perceived by the nose, but it may take a minimum of one part per thousand to stimulate the taste cells. The human nose may be able to discern an almost infinite number of smells. In contrast, humans are able to distinguish several million different colors, over 300,000 audio tones and five basic tastes. Once they are sensed, then odors are transmitted to the brain where they are interpreted, identified and often acted upon rapidly. The only other bodily system that utilizes chemicals in a similar manner is the immune system that identifies, gives significance to, and memorizes new molecules. Along with hunger, the sense of smell drives humans to eat and drink, and this drive is mainly for carbohydratecontaining foods and beverages, which are the body’s main energy source. Since the body’s most sensitive receptors are for smell, people do smell and seek out carbohydrates for energy. They are driven to the sweet smell of baked goods or sweetened beverages, for example, because they generally signify a sign of calories to come. While the sense of smell is so easily stimulated, it is also very fragile and may easily deteriorate or fatigue. Some adaptations may be short term; other modifications may take more time, or they may not return fully. Identification of smell losses with mechanisms for changes is key to olfactory recovery [2]. Due to beliefs, cultures, genes, past experiences and a host of other reasons the same scent might be perceived differently from one individual to another. Disease processes that cause or are associated with smell disorders may be fleeting (as in a cold), metabolic (as in vitamin or mineral deficiencies) or permanent (as in head trauma or tumors). With aging, there appears to be a decline in the sense of smell, although many individuals may not be aware of this debility until food tastes poorly or there is undetected chemical exposure. While there are tests that measure the loss of smell, regular examinations and evaluations by healthcare professionals may identify olfactory losses before they become critical. Discovering about the process of olfaction and how it affects taste, flavor and environmental toxin identification is an important step in this direction [3].

THE SENSE OF SMELL (OLFACTION) The sense of smell, or olfaction, allegedly was detected in ancient times. Lucretius, an Epicurean and atomistic Roman philosopher during the 1st century BCE, speculated that different odors are attributed to different shapes and sizes of odor molecules that stimulate the “olfactory organ.” Hundreds of years later in 2004, olfactory researchers Linda B. Buck and Richard Axel were awarded the Nobel Prize for the cloning of olfactory receptor proteins and subsequent pairing of odor molecules to specific receptor proteins. This discovery confirmed that like taste and taste receptors, odor molecules are detected by odor receptors [4]. So like gustation or taste, the sense of smell or olfaction is a type of chemoreception: a physiological process whereby organisms respond to chemical stimuli. Humans and other “higher animals” have two primary types of chemoreceptors: taste or gustatory, and smell or olfactory. Similar to gustation, the olfactory sensory system relies on molecular chemical compounds within substances to distinguish environmental data. While gustation depends on the main sensory structures involved with taste, olfaction depends on the nasal cavities with their olfactory receptors and the transduction of odors from the environment into neural impulses. Olfaction is closely tied to gustation, as well as to the other senses of sight (vision), sound (audition) and touch (somatosensation). Olfaction is also the sense that is closely connection with memory, due to its close neural networks to the parts of the brain that are responsible for emotion and place memory [5]. When olfaction works in conjunction with gustation to perceive complex flavors, this interaction is referred to as chemoreceptive sensory interaction. If the olfactory or gustatory systems are compromised (as they may be with differing conditions and/or with aging), then foods and beverages may smell, taste or smell and taste differently. This is one of the reasons why olfaction is so essential to life—in fact, about 5% of human DNA is devoted to this basic sense. Early in the lifecycle, the sense of smell may elicit orientation and movement toward maternal odors in newborn babies. Later in the lifecycle, the sense of smell may trigger some humans to follow a scent trail. With training, it is thought that humans might be capable of doing tasks that were considered to be the exclusive domain of nonhuman animals. For example, as people age and their eyesight diminishes, their sense of smell might be able to help them maneuver their environment, much like some animals use this sense to master their surroundings [6]. AGING, NUTRITION AND TASTE

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The Olfactory System Odorants, or odor molecules, are chemicals that are vaporized and travel via the air to the nostrils. Typically odorants encounter the cilia of the sensory neurons that are immersed in a layer of mucous on the roof of each nostril where they dissolve. Specifically, sensory receptors, also called chemoreceptors, are enmeshed within the olfactory epithelium, a patch of tissue similar in size to a postage stamp that is highly situated in the nasal cavity. The olfactory epithelium is composed of sensory neurons with each containing a primary cilium, supporting cells and basal cell that replenish the sensory neurons that perish. The olfactory epithelium is where the neurons detect different odors; in fact, they are capable of detecting literally thousands of various odors so their integrity is of upmost importance. Once the odorant molecules dissolve in the mucus lining they bind to the receptors on the cilia. These are referred to as transmembrane proteins. This process then activates a G protein that is coupled to the receptors, and then adenylyl cyclase (AC), an enzyme that is rooted within the cilia’s plasma membrane. AC catalyzes the conversion of adenosine triphosphate energy to cyclic adenosine monophosphate (cAMP). In turn, cAMP opens sodium channels that diffuse sodium into the cells, that generates an action potential when a threshold is reached. This action is conducted along the olfactory nerve to the olfactory bulb at the back of the nose, where sensory input interacts to identify the smell(s), and to evoke smell memory(s) and emotion(s) [7]. The sensory receptors within the olfactory bulb accomplish this action by sending messages to the most primitive parts of the brain (the limbic system structures where emotions and memories are influenced). The limbic system is composed of connected structures within the middle of the brain, and is linked with the central nervous system (CNS). These structures work collectively to affect many behaviors that include emotions, memory and motivation, and are more automatic or instinctive versus intentional in nature. The limbic system is also responsible for the translation of sensory information from the neo-cortex into motivational forces that promote certain behaviors. Messages that are sent to the neo-cortex, or higher center of the brain, may modify a person’s conscious thoughts. When the primitive and the higher-brain centers combine efforts, they are capable of perceiving smells, accessing smell memories and evoking emotions in reaction to a wide range of smells. The human sense of smell is more sensitive than other senses, so smell recognition may be fairly instantaneous. In comparison, the senses of taste and touch need to communicate through neurons throughout the human body and the spinal cord before they reach the brain. This system provides direct exposure from the environment to a person’s CNS, and is one reason why toxic smells may potentially be dangerous [8].

Emotion More than any other sense, olfaction successfully activates emotions and memory. This may be because the olfactory bulb directly connects to two brain areas with significant implications for emotion and memory: the amygdala and hippocampus. The amygdala is one of two almond-shaped groups of nuclei that is located deeply and medially within the temporal lobes of the human brain, and is considered to be part of the limbic system. It has a primary role in decision-making, emotional reactions and memory. Older adults tend to show less amygdala activity than younger adults; however, less amygdala response to negative stimuli is not necessarily an indication of poor function. The hippocampus is also located in the medial temporal lobe of the human brain and is also a part of the limbic system. It performs vital functions in the consolidation of short and long-term memory and in spatial memory that facilitates navigation. In Alzheimer’s disease, the hippocampus is one of the first regions of the brain to deteriorate. Auditory, tactile and visual information are not processed within these brain areas. While the perfume industry has developed state-of-the art creative packaging for visual appeal, fragrances are developed for their emotional responses: desire, earthiness, power, relaxation, sweetness and vitality and the nuances of other esoteric responses. The sense of smell is also very important from an emotional perspective with regard to the social/sexual attraction between people. Human body odor, produced by genes that make up the immune system, assist in partner selection. Sniffing, smelling and tasting (through kissing) either confirm or negate a match.

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Emotional responses to smells are generally ruled by connections: individual perceptions of the same smell(s) may be experienced differently. This may be the case with perfumes that appeal to a wide range of consumers, but may be repugnant to others. Very offensive smells, such as rotten food, smoke or toxic chemicals, may elicit universal emotional responses [9].

Memory People who have full olfactory function may be able to recollect specific smells that evoke distinct memories. The experience may occur instantly as when one walks into a bakery and smells a particular style of fresh bread or pastry. Due to the olfactory bulb’s positioning within the limbic system, or emotional brain, smells rarely have a neutral reaction if the olfactory system is intact. Even an unborn child that is exposed to certain environmental substances (such as cigarette smoke) or tastes (such as odorous garlic or onions) may demonstrate a preference or dislike for them after birth. Explicit memory is a term that describes the memories that are recalled by conscious thoughts. With regard to olfaction, explicit memory attributes associative meaning to odors and to nonodor stimuli. It includes information to process and compare confronted odors. Odor recognition and identification are common tests for explicit odor memory. Implicit memory is a term that describes the memories that do not require conscious recollection of the initial encounter of an odor. For odors to form in the brain, deliberate recollections of odor experiences are not essential. Common tests for implicit memory include those that measure previous exposure to similar stimuli: classical conditioning, habituation, perceptual learning and/or sensitization. These types of tests may be especially useful in evaluation of brain injuries. Measures to utilize smell memory for invoking pleasant thoughts about beverages, foods and dining experiences may be found within the upcoming section on Improving the Sense of Smell.

Habituation The concept of habituation refers to decreased responsiveness to odors due to prolonged exposure. It involves decreased attention and sensitivity to stimuli that may no longer appear to be novel. This is may be due to the adaptation of receptor neurons in the olfactory system in reaction to certain odors. During habituation, fewer neurotransmitters may be released at the synapse. Yet, in sensitization there are more presynaptic transmitters. Also, the neuron itself tends to be more excitable. The neurotransmitter norepinephrine is thought to have effects on olfactory functioning with regard to habituation [10].

Motivation Motivation is closely related to emotions in the brain where smell information projects into the medial temporal lobe near the midline of the cerebrum. The limbic system’s network of connected structures that are linked within the CNS work together and affect a wide range of behaviors. Motivation is also concerned with translating sensory information from the neo-cortex, or the “thinking” area of the brain, into motivation or incentive that translate into behaviors. This anatomically interconnected network of nuclei and cortical structures is critical to the survival of individuals and species that includes the identification of predators, the location of food and the recognition of individuals for procreation or social hierarchy. Complex behaviors may be modulated by odors and prompted by motivations to produce adaptive responses. Humans who are compromised in their senses of vision and/or hearing may rely on their other senses, namely smell and taste to compensate. They may be motivated or inspired to perform or undergo certain activities that are based on environmental factors, such as pleasing aromas. For example, the wafting smell of freshly baked cookies may arouse a person’s hunger even if she cannot see the cookies. Or chemosensory compromised older individuals may be motivated to taste a very aromatic soup if they take a deep whiff—despite not being able to adequately see its contents.

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Cognition (Conscious Thoughts) Cognition, or conscious thoughts, may significantly influence the perception of smell. Humans possess unique abilities to detect and discriminate odors. They tend to have less ability to identify certain odors. This may be due to lack of language skills to describe particular odors that tend to be more sensory than cognitive in nature. Olfactory cognition has some features in common with auditory and visual cognition, but it is also unique. Of concern is that mild cognitive impairment and Alzheimer’s disease have been demonstrated in olfactory dysfunction. While age is associated with decline in many cognitive functions, some cognitive changes might also indicate a disease process that may culminate in dementia. A noticeable loss of smell has been correlated with neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease and other forms of dementia. Demographic and genetic factors may also interplay. The olfactory receptor neurons (ORN) also known as olfactory sensory neurons (OSN) have two notable properties: the first is that they are nerve cells that are closely related to nerve cells in the brain, and the second is that they continually regenerate throughout the lifetime, unlike brain nerve cells. A decline in olfactory performance may be indicative of changes in the functional or regenerative abilities of the ORN. This condition may also signal neuronal deterioration. If any changes are questionable, smell identification tests may be warranted [11]. The University of Pennsylvania Smell Identification Test (UPSIT) can be used to test the functionality of an individual’s olfactory system. It measures a person’s ability to detect odors at a suprathreshold level. The UPSIT has application in the diagnosis of conditions and diseases that are classified as degenerative neuropsychiatric disorders. These include acquired immunodeficiency syndrome, Alzheimer’s disease, brain tumors, congenital anosmia, head trauma, Huntington’s disease, Korsakoff’s psychosis, multiple sclerosis, Parkinson’s disease and/or schizophrenia. More information about these conditions and/or diseases can be found in Chapter 8, Meeting Nutritional and Disease-Specific Needs of Aging. As people age, they may undergo several stages of olfactory dysfunction. Individuals with the most dysfunction also tend to be the ones with the most pathology, such as Alzheimer’s or Parkinson’s disease.

HOW SMELLS ARE PERCEIVED As with the sense of taste, olfactory sensation depends on a finely wired messaging system. This is dependent upon olfactory receptor cells in the nose and electrical messages via the olfactory nerve to the olfactory bulb, where the brain’s first processing of these sensations occurs. Each receptor is reportedly unique and ascribed to just one type of olfactory receptor. As nerve axons travel to the olfactory bulb, they coalesce to form hundreds of glomeruli, or tiny spheres. Each of the glomerulus obtains axons from the nose cells with a similar type of olfactory receptor. This is where the finely wired messaging system really interplays. The glomeruli are activated by many different receptors and the pattern is unique depending on the smell(s). This unique configuration is processed by the olfactory bulb, then dispersed to other areas of the brain. This distribution includes the limbic system where emotion and memory come into play, the olfactory cortex where conscious awareness is added and the orbitofrontal cortex where feedback from other sensory systems is obtained [12]. Rarely does a person have neutral reactions to smells. Rather, many reactions are based on pure emotional associations. By the time olfactory cognition correctly identifies and names a smell, the smell has probably activated the limbic system and triggered a deeply rooted emotional response. Take the scent of vanilla, for example. While the scent of vanilla is commonly thought to be a sweet and pleasant smell that influences mood and the sense of well-being (consider the strong scent of vanilla in body care products), it may actually be the expectations of the vanilla aroma that affect disposition and health benefits. This is why the use of the word vanilla in foods and beverages may evoke a happy feeling even before they are consumed. This may also be one of the reasons why vanilla ice cream is the most popular flavor of ice cream in the United States. The use of pleasant fragrances continues to have positive effects on mood, despite the projected decline of olfactory sensitivity as people age. Perceived differences in the stimulation of right and left nostrils with pleasant fragrances (such as vanilla) indicate differences in olfactory cortical neuron activity in the right and left hemispheres of the brain. The left hemisphere has shown predominant processing of positive emotions, while the right hemisphere has shown

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predominant processing of negative emotions, which may be produced by the perception of unpleasant fragrances [13]. By enhancing or altering smells, it may be possible to modify how smells are processed and the emotions that are evoked. For example, in the example of the cookies described in the previous section on “Motivation,” the amount of vanilla in the cookie recipe could be doubled to boost the vanilla aroma. This may be particularly helpful for people with dementia if they have forgotten the smell and/or taste of cookies altogether. Conversely, if ground nuts (with a bitter taste) are used in the cookie recipe, then the enhanced vanilla flavor may not only boost the sweet taste, but may also serve to camouflage any bitterness [14].

Expectations Not only do smell and taste expectations influence a person’s taste ratings of foods and beverages, but they also may influence the consumption of accompanying foods. In other words, if people expect a delicious food or beverage, then they may consider the rest of the meal equally delicious. This concept is called “expectation assimilation.” It may also work in the opposite manner: if one anticipates that a food, beverage or meal will smell or taste poorly, then it just might happen. Additionally, brain imaging research demonstrates that as people consume what they consider to be an expensive beverage, areas of the brain that are linked with pleasure are more activated than if they think that the beverage in inexpensive [15]. Scent signals may also be affected by the milieu in which one encounters them; by how they are “packaged” (as in bottles, cans, cartons, etc.); and when and where they are sensed. Visual cues should also connect with expected scents, such as peaceful or stimulating images in conjunction with soft or rousing aromas (e.g., the smell of cotton candy and summer at the beach, versus blackened marshmallows and a fireplace hearth) [16].

Interpretations The manner in which scents are interpreted involves the areas of the brain that process the electrical signals that travel from the sensory neurons to the olfactory bulb. One of these areas is called the piriform cortex, a collection of neurons located just behind the olfactory bulb that function for smell identification. Other smell information travels to the thalamus, which functions as a “relay station,” or transmitter for sensory information that travels into the brain. Some smell information is transmitted from the thalamus to the orbitofrontal cortex where it is integrated with taste information. If any of these brain areas are compromised by age, disease or impairment, smell identification might be compromised. In the limbic system the smell(s) are interpreted in relation to past experiences. Then the smell(s) are processed and transmitted through a pathway to the CNS that manages cognition, emotions and behaviors. Reactions may be, “I like that smell since it reminds me of my grandma’s chicken soup, and I’d like to have some right now,” versus “I do not like that smell because it reminds me of my uncle’s cigar smoke that infiltrated our bread, so I don’t want to eat it!” [16].

Evolutions Global studies of genes have helped to provide insights into how the taste for different foods and beverages may have been influenced by variations in the ability to smell. In turn, the sense of smell, as it is linked to foods and beverages, has played decisive roles in human societies. Likewise has the identification of pleasant and unpleasant substances, edible and nonedible.

Genes The smell receptor OR7D4 enables humans to detect androstenone, a very specific odor that is produced by pigs and found in boar meat. If people have different DNA sequencing in the gene that produces the OR7D4 receptor, then they may respond different to this odor.

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Populations that have different gene sequences tend to respond differently in their ability to detect this substance. Humans evolved from African roots where populations were able to detect this odor, as opposed to populations in the northern hemisphere. This is just one example of how gene sequencing is so diverse and has evolved to affect odor acceptance or rejection. For most mammals, the sense of smell is dominant. Humans have fewer olfactory receptors than dogs or mice. But the gene family is still large. The human genome contains around 900 genes and pseudogenes (genes that have either lost their ability to produce proteins, or fail to produce them within a particular type of cell) that are associated with smell perception; this provides some idea about how difficult it is to gain access to individualized smell perception and assess its decline. In humans (as compared to other species) the number of human olfactory receptor genes may be more pseudogenes than genes. Emotional stress, the act of eating, the immune system, reproduction and social communication may be individually or mutually involved [17].

Infants The human fetus may detect smells even before childbirth. Amniotic fluid is sweet and so is human breast milk. Right after childbirth, an infant may be able to detect early breast milk and seek its first breastfeeding. After the first trimester of pregnancy, the fetus may be able to smell the foods and beverages that the mother is consuming. Smell is the predominant sense because it can cross the amniotic fluid. The senses of smell and taste are considered to be the most powerful at birth, while the sense of hearing fully matures about 1 month after birth, and the sense of sight develops progressively throughout the first year of life. After the end of the first week of an infant’s life, its nose is so finely adapted that the infant may be able to discriminate among different types of breast milk, if necessary. By 1 month of age, an infant might find strong aromas to be overwhelming. These strong scents might interfere with its sense of taste, so it is advisable to avoid fragranced skin care products and/or very odorous perfumes. By 3 months of age an infant may be able to discriminate among the people in their life by their aromas. By 6 months of age when many US babies are weaned to solid foods, the aromas and tastes may begin to dictate preferences or rejections. Then by 10 months to 1 year of age, an infant’s sense of smell and taste may make feeding more challenging, as food and beverages predilections really begin to occur. Flavor complexity depends on food odor. While food odor permits a person to discriminate among the subtle differences amid foods and beverages (such as members of the “stone” family with its apricots, peaches and plums), it may also be overwhelming (such as the odorous Brassicaceae family that includes broccoli Brussels sprouts, cabbage and cauliflower). Food odor familiarity may be essential to help foster healthy feeding experiences.

Pregnancy Anecdotal reports of increased olfactory sensitivity and hormonal changes before and during pregnancy are common, although the scientific literature may not unconditionally support these reports. Olfactory sensitivity during pregnancy may function as an evolutionary mechanism to protect the developing embryo from environmental substances or ingested toxins. This heightened sensitivity may trigger nausea and/or vomiting during pregnancy. It is known that there is a complex interaction among hormones that underlie olfactory perception during pregnancy, estrogen being one such hormone. Human chorionic gonadotropin (hCG), a hormone that is produced by the placenta after impregnation, may stimulate the hormone estrogen. Estrogen levels tend to rise during pregnancy and reach their peak right before childbirth. Incidents of nausea and vomiting may also be correlated with hCG levels during pregnancy [18].

Adulthood While a decline in the sense of smell and taste may happen anytime during the lifecycle, due to such factors as the common cold or influenza, head trauma, nasal and/or sinus blockages and others, there may be more dramatic changes in both olfaction and gustation with aging.

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Individual ORN in healthy aging people may be less selective in their responses to odors. While they may respond to a wider range of odorous substances, they also may provide less discrimination among odors [19]. An acute sense of smell may last until age 50 or 60; then older adults may experience a subtle or radical decline, with more major chemosensory changes in the 70s and 80s, according to the 2015 2016 National Health and Nutrition Examination Survey. Definitive comparisons of chronological age and decline in cognition and olfaction characteristically require individualized examination and prognosis. Age-related anatomical and structural losses in the CNS may affect both cognition and olfaction in older adults. These may include plaques and tangles in the anterior olfactory nucleus, hippocampus and parahippocampal gyrus of older adults aged 54 89 years who may not exhibit any signs of dementia. These neuropathological changes have not commonly been reported in younger adults, yet are thought to underlie olfactory dysfunction in this older age group, and are hypothesized to affect the cognitive performance of certain tasks during adulthood and advancing years. It has been conjectured that olfactory modality is a valid marker of CNS function, especially in older adulthood, and may be further suggested as a potential measure of brain integrity. Other reputed factors for olfactory decline after early adulthood include pathological changes at both the peripheral and central levels. Many of these changes are listed in Table 5.1. TABLE 5.1 Pathological Changes That Hasten Olfactory Decline • Alterations in the regulation of intracellular calcium levels • Atrophy of the olfactory bulb and in the olfactory tract • Changes: neuropathological in the mesial temporal lobe and the orbital frontal cortex • Decreased glomeruli and mitral cell numbers • Dementia • Diseases: nasal and/or sinus • Head trauma • Increases in the amplitude and prolonger excitation of calcium potentials • Leakages of synaptic transmitters • Longer latency and smaller amplitudes in cognitive and sensory components • Medications • Ongoing smoking • Shifts from more activity in central and parietal electrode sites to the frontal sites [20]

Individuals who lose their sense of smell as they age may be at greater risk of neurological disorders, particularly Alzheimer’s and Parkinson’s disease. They may also be at greater risk of dying shortly after their loss in olfactory function is determined, since the loss of smell may be a factor in overall bodily decline. Treatments to maintain or protect future olfactory decline appear to be limited. Smell training, an approach whereby individuals may train their nose to detect strong smells such as cloves, eucalyptus or lemon through daily whiffs, may produce some beneficial results. Implanted devices to help the brain process odors as distinctly as during younger years may be forthcoming [21].

TYPES OF AROMAS Contrary to the five basic tastes of acidity, bitter, salty, sweet and umami, attempts to quantify and quality aromas may seem unwieldy. By examining the essence of aromas, their impressions and reactions, some clarity may be established for baseline interpretations and potential applications.

Aroma Categorizations An aroma is a distinctive and noticeable smell or scent. It generally connotes a pleasant quality. In contrast, a repulsive smell or scent is generally referred to as an odor. But the words aroma, odor, scent and smell are often used interchangeably.

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At the beginning of the 20th century, German psychologist Hans Henning (1885 1946) postulated that there were only six categories of smells and combinations of smells that characterized all of the detectable aromas and odors. These included burned (such as burnt toast or tar oil); ethereal (such as cleaning fluid or ether); flowery/fragrant/fruity (such as lavender or rose); putrid (such as decaying fish or rotten eggs); resinous (such as resin or turpentine); and spicy (such as cinnamon or nutmeg). Some thought was that flowery, fragrant or fruity was one of the six primary odors. Henning arranged these classifications into an odor or smell “prism”; an olfactory model with the primary odors located at the corners and the complex odors shown on the edges, face and sides of the prism. Many criticized this arrangement as too impromptu and restrictive [22]. Contrary to the senses of hearing or vision that are connect to measurable physical phenomena, the sense of smell is much more difficult to quantify as a systematic interpretation of which smells are perceived and how they compare to physical phenomena. Part of this conundrum may be that an individual’s perception of an aroma is highly personalized, and furthermore, it may be difficult to extrapolate into an objective label. Pleasantness and/or unpleasantness, learning, context and memory may all interplay. This puzzle has applications in both the food and cosmetics industries. In the world of perfume, aromas have been classified as camphoraceous, citrus, earthy, floral, herbaceous, resinous, spicy or woody and others to help attract and/or match individual preferences. In the realm of food (as opposed to the five basic tastes) another aroma schematic suggests that there may be 10 basic categories of aromas that are based upon a classification that utilizes odor character profiles—once again, taking individualized nuances into account. This helps to demonstrate that while individuals may not necessarily like or dislike an aroma, each aroma may play an important role and interplay in everyday life, from luxurious enjoyment to the assurance of human survival [23].

Multidimensional Aroma Classifications Still another method for describing odors involves their multidimensional characters. According to this approach, the spaces that odors occupy are not homogenous. Rather, it is proposed that they exist in a discrete and intrinsically clustered manner. Also according to this process, aroma clusters include such impressions as chemical, decayed, fragrant, fruity (noncitrus), lemon, minty/peppermint, popcorn, pungent, sweet and woody/resinous. • Chemical aromas include those from bleach, gasoline, household cleaning supplies, markers, nail polish and nail polish remover and paint. A food or beverage may smell of chemicals depending on the degree of enrichment (such as protein, vitamins and/or minerals) or fortification. • Decayed aromas incorporate those from burnt rubber, household gas, sewage or sulfuric acid. They are usually putrid and sickening in nature. Decayed aromas may be nature’s sign that a food or beverage is too repugnant to consume and may lead to illness if ingested. • Fragrant aromas are described as those from cologne or perfume: floral, flowery, grassy, intoxicating, herbal, light, natural or rosy. When a food or beverage is deemed fragrant, it often means that that it has a hibiscus, jasmine, lavender, orange blossom, rose, vanilla or other similar aromas. • Fruity (Noncitrus) aromas are described as fresh and light aromas that are connected with such foods as bananas, peaches, strawberries or vanilla and fragrances with similar ingredients or scent profiles. As opposed to citrusy aromas, fruity aromas tend to smell fruitier, silkier or smoother, compared to the acidity from citrus fruits, such as grapefruit, lemon, lime or orange. • Lemon is a very popular aroma in both the food and beverage and fragrance domains. It has a connotation of freshness and suggests that lemon-scented cleaning supplies not only cleanse but revive. When used in cooking and baking, lemon has the capability of brightening foods and beverages when they may taste or smell flat, or when the ingredients in a dish need to be unified before consumption. • Minty/peppermint, like the aroma of lemon, suggests cleanliness and freshness, and is one of the main reasons while this aroma is used in oral hygiene products. The minty/peppermint aroma is also described as cool, exhilarating and spicy. It contributes an adult-like smell and taste to foods and beverages, such as mint jelly that is often served with lamb chops or minted tea. Minty/peppermint may also provide some gastrointestinal comfort, and for this reason they are frequently used in medications.

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• Popcorn is a distinctive aroma that usually implies pleasant memories, often from childhood. Other distinctive aromas that are grouped in this category include caramel and peanut butter, with their burnt, heavy, nutty and warm aromas and tastes. However, because the aroma of popcorn is so distinctive, it may overpower a food when it is used as an ingredient, so it may have limited applications. • Pungent aromas are often deemed as sharp and for good reason: they are usually easily discernible at their first whiff. Pungent aromas include repulsive substances such as sour or spoiled milk or other dairy products or fecal matter or sweat. However, pungent aromas may also include garlic and onion aromas if they are overwhelming to some individuals. In some countries, pungent/sharp ingredients are valued for their culinary touches such as very pungent cheeses or fermented foods and beverages that may also have gastrointestinal health advantages. • Sweet aromas include almond, chocolate, malty and vanilla scents. Sweet aromas also capture the sweetness in very ripe and fragrant fruits, especially bananas, berries, melons and pineapples. Sweetness is also used to describe the aromas in aromatic baked goods, including breads, cakes, cookies and pastries, and from the caramelization of sugars in the baking process. • Woody/resinous aromas bespeak the outdoors. They are often referred to as the scent of nature, and include reference to burnt, earthy, exotic, green, heavy, tobacco, moldy, musky, musty, Oriental, smoky and woody smells and others. Some think that woody/resinous aromas are more masculine in nature. For this reason, many aromas of this kind are used in men’s fragrances and body care products, and they may have universal appeal—particularly for active individuals [23].

AROMAS AND AGING The ability of humans to detect certain aromas is disputable. This is because smell sensitivities may vary widely from person to person according to factors that include cognition, genetics, perception and physiology— and specifically his or her amount of olfactory receptors. Unless they are identical twins, no two individuals will probably possess the identical genetic make-up for olfactory receptors. One explanation is that genes have mutated throughout evolution. This may be why smell has gradually become less important for survival than color vision, for example, in the identification of rotten food or toxic substances. Another explanation is that proteins may be the biological determinants of smell detection. Proteins ensure that the signals that are produced by the olfactory receptors are effectively transmitted to the higher processing areas of the brain. Proteins may hold the answer to why some people have higher than average smell sensitivities, while other people are more sensitive overall to some smells versus others, and why still other people may seem to have no sense of smell at all [24]. It is suspected that there may be at least one odorant that a person cannot detect at all. This is referred to as a specific anosmia, or as an olfactory blind spot that is likely inherited. For example, some wine drinkers may be “smell blind” to specific chemicals, such as TCA (2,4,6-trichloroanisole, a chemical substance known as “cork taint” that is common to “corky” wines), while others may seem to tolerate it. Specific anosmias may be related to the molecular weight of an odor, and they may become more common as the molecular weight of an odorant increases. A heavier, more complicated odor molecule might have a more difficult time binding with one specific smell receptor and become undetectable—particularly if the smell receptor’s gene becomes a pseudogene. Once damaging mutations occur in certain genes, then these genes may stop producing working receptors and become pseudogenes. As previously mentioned, these pseudogenes may vary among individuals and form different combinations of olfactory sensitivities. Genetic variability in olfactory sensitivities may also be reflected in behavioral variability. While people may not be conscious of smelling anything, they may still display physiological responses to odorants, both conscious and otherwise. For example, a spicy odor may not register at all, or as strongly liked or disliked odor, but it may still provoke increased skin conductance, from slight perspiration and/or warming at the thought of consuming spicy foods or beverages. Sensory perception and sensory loss with aging, like in the younger years, is dependent on intact olfactory sensory neurons. To better understand the crucial roles that they play in olfaction throughout the lifetime and particularly throughout aging, it is logical to examine their response(s) to various stimuli during the aging process.

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Olfactory sensory neurons respond to many diverse odorants if they share common features. For example, olfactory sensory neurons may not selectively respond to chocolate or vanilla flavors, but they may respond to the chemical groups that are found within these flavors (such as alcohols or aldehydes). In the brain, the olfactory bulb and olfactory cortex collectively serve to (1) examine the combinations of sensory neurons that are activated at any given time, (2) translate these patterns in the context of previously experienced patterns and (3) interpret the smell or smells. These olfactory sensory neurons simply do not live forever; in fact, they expire and are usually replaced throughout life. This may be in contrast to aging when they may perish and may not be replaced. Fortunately, all of the sensory neurons do not die simultaneously. A small subset of sensory neurons may fail, and the resultant patterns of activities that the olfactory processing regions of the brain receive may be somewhat affected. However, and in general, there is remarkable stability throughout a lifetime. For the most part, new neuron axons connect to the same group of olfactory bulb neurons as existed before their death. This “rewiring” process generally continues until the close of the lifecycle. Then the sensory neurons may die and may not be replaced [25]. Several studies have demonstrated age-related changes in olfaction in humans that may involve sensory neuron dysfunction or demise. These include decreased odor discrimination, decreased odor memory, decreased smell identification and/or increased odor detection thresholds. Additionally, those who are aging appear to be more prone to olfactory adaptation, and slower to recover threshold sensitivity than younger adults. For example, when older people are exposed to a suprathreshold level of an odorant, such as garlic or onions, they may recover slower than younger people who have progressed to new odorants [26]. Retronasal smell, or the ability to smell through the back of the mouth to the rear of the nose, also tends to decrease with aging. There may be many issues for this decrease in occurrence. These include the multitude of mental and physical changes that occur during aging, prolonged use of medication and the use of dentures that may affect the perception of both odors and tastes. Insensitivity to food odors that are produced retronasally may not be recognized during actual food consumption, since most food odors are identified nasally. Individual differences in odor responsiveness that are generated retronasally may become even greater with age. The ability to sense salty and sweet tastes may decreased sooner than the ability to sense bitter or sour tastes because the anterior taste buds (which are responsible for the salt and sweet tastes) seem to be affected first by aging. The posterior taste buds for bitter and sour seem to be affected later, but both of these conditions may be highly individualized and variable. Since aromas are so closely associated with taste, suprathreshold losses in the perception of the sweet and salty qualities of foods and beverages may have health consequences in the aging. For one, decrease in suprathreshold sweet taste perception may increase the possibility that people with diabetes consume excess sugar. Likewise, decrease in the suprathreshold salty taste perception may make it more difficult for hypertensive patients to comply with strict salt (NaCl) restrictions [27]. Specific odors that signify a certain deleterious food or designate danger may alter an animal’s potential lifespan and physiological profile. These odors may accomplish this through the activation of many highly specialized sensory neurons. Carbon dioxide (CO2) is the first well-defined odorant that is able to modify physiology and influence aging in laboratory specimens. Carbon dioxide may stimulate the trigeminal nerve responsible for facial sensation and motor functions [28]. Insect studies have demonstrated that that the incapability to smell CO2 is associated with longer lifespan, more resistance to stress and increased body fat. CO2 is said to be an ecologically important odor cue that is indicative of animal blood, distress (it is implicated as a stress pheromone) and/or rotting food. It has been postulated that similar effects may be evident in humans but that more research is warranted [29]. The human ability to discriminate odors in a mixture may be limited. So it makes sense that simple foods with distinct aromas are created and presented to those who are aging. This way aging people are better able to discriminate individual smells and assign their likes and dislikes. When a recipe is mixed with multiple ingredients and is accompanied by other recipes with a variety of dressings, herbs, sauces and/or spices it is not surprising that aging people are confused and reject mixed dishes, much like some children and their insistence for singular tastes. For individuals who reportedly have lost some or more of their sense of smell, chemosensory enhancement by the use of certain ingredients and techniques may be useful. These strategies may help aging people to remember how certain aromas or odors used to smell when they were younger so that they may regain their approval. Examples are provided in Chapter 6, Flavor Enhancement Ingredients, and in Chapter 7, Flavor Enhancement Techniques.

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SMELL AND BEHAVIOR The sense of smell is inextricably linked with behavior and has been throughout human evolution since it has been aligned with survival. Olfaction drives behavior both at the instinctive and subconscious levels. For instance, a negative smell such as rotting meat may instigate an impulse to take heed while a positive smell such as cinnamon with its sweet-spiciness may conjure up pleasant, safe and secure life experiences. The idiosyncrasies of olfactory perception may be formed by cultural and geographic variations and by personal history. In the United States, the aroma of citrus is characterized as bright (consider the array of household and personal care products with this scent); the aroma of peppermint is considered as arousing; and the aroma of lavender is regarded as calming—also as evidenced by products with these fragrances. On the contrary, in the Far East, a soothing aroma is thought to be jasmine, while orange or rose water is considered to be energizing. To those who are aging, lavender and rose may be scents that are reminiscent of yesteryear, lemon or orange may connote a younger or more vibrant aroma and jasmine may designate a more exotic fragrance. Scents such as these may be important in settings where the aging have lost some of their sense of smell. Prosocial behavior has been shown to be significantly greater when people are exposed to sweet fragrances, such as the aromas from baked cookies or warm chocolate. These aromas may also help aging people with dementia remember these enjoyable scents and the pleasant associations from the past that they evoked [30]. Behavioral and psychological symptoms of dementia (BPSD), also known as neuropsychiatric symptoms, may occur in differing degrees in people with dementia. They may vary according to the degree of cognitive and functional impairment. These symptoms may include aberrant motor behavior, agitation, anxiety, apathy, appetite changes, delusions, depression, disinhibitions, elation, hallucinations, irritability and/or sleep changes due to genetic, neurochemical and/or neuropathological factors. Aromatherapy is a nonpharmacological intervention that has been used to treat the symptoms of BPSD, and is generally recommended as first-line treatment followed by the least harmful medication for the shortest possible period of time. Evidence about the efficacy of various psychotherapies has been insufficient, but if and when they are individualized, then some psycho-educational interventions may be longer lasting. Sensory interventions such as aromatherapy, environmental modifications and music therapy have been shown to be useful to reduce agitation in some people with dementia [31]. Aromatherapy is based on the use of therapeutic oils that are extracted from barks, bushes, flowers, leaves, peels, shrubs, stems and trees to help support equilibrium, health and well-being. These essential oils are based on naturally forming chemicals, many of which have antifungal and antiviral properties that have been used in traditional medicine by ancient civilizations for thousands of years. They are typically colorless mixtures of alcohol, aldehydes, esters, ethers, ketones, oxides, phenols and/or terpenes that may produce characteristic odors. Essential oils help to provide their beneficial effects through absorption and inhalation. A summary of the plant parts that are used in the preparation of essential oils is provided in Table 5.2. TABLE 5.2 Parts of Plants That Produce Essential Oils Parts of plants

Essential oils

Bark

Cinnamon

Flowers

Jasmine, orange blossom, rose and ylang ylang

Leaves

Citronella, lemongrass, palmarosa, patchouli and petitgrain

Peels

Bergamot, grapefruit, lemon, lime, orange and tangerine

Roots

Ginger and vetiver

Whole plants

Geranium, lavender, rosemary and rose

When absorbed into the skin via baths and/or local application by massage, essential oils may pass through the epidermis and into the blood stream. If essential oils are inhaled, they may deliver aromatic molecules that are sensed by receptor cells in the nose, and then transmitted to the limbic system and the hypothalamus via the olfactory bulb. These signals then may cause the brain to release neuromessengers, such as endorphins and serotonin, which link the nervous and other body systems into desirable actions or changes that may include the feeling of relief. Thus, the essential oil connection with relaxation is suggested. AGING, NUTRITION AND TASTE

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For example, essential oils may serve as springboards for neurochemicals that are released by the brain on their own, or with the assistance of hormones that are released by the body, to help to regular blood pressure, slow the heart rate and stimulate the immune system, among other functions. Their stimulating properties may be the result of their structures that have been said to resemble some hormones. When the essential oils are within the body, then they may remodulate and focus on certain targeted areas. As a result, behavior, mood and productivity may be affected. In particular, serotonin is said to be released by calming essential oils, endorphins by euphoric essential oils and noradrenaline (NA) by stimulating essential oils. It is important to note that some of these associations may be speculative [32]. Different types of essential oils are often used in aromatherapy as shown in Table 5.3. Their outcomes may be both variable and conjectural. Often considered as alternative therapies or “home remedies,” some have migrated into mainstream usages. It is important to first check their usage with health care professionals to ensure their safety.

TABLE 5.3 Applications of Essential Oils in Aromatherapy Essential oils

Applications

Almond, jojoba or grape seed

Healing

Angelica

Fatigue

Basil

Exhaustion

Bergamot

Agitation, anxiety or stress

Chamomile

Hay fever, inflammation, gastrointestinal disorders and rheumatic pain management

Citronella

Fatigue

Eucalyptus

Headache, neuralgia, joint and muscle pain and immunity

Everlasting

Exhaustion

Frankincense

End-of-life

Germanium

Anxiety, emotions and stress and skin disorders

Ginger

Fatigue

Juniper berry

Insomnia

Lavender

Agitation, anxiety or stress, circulation, digestion, end-of-life, immune system, joints and muscles, respiration and skin care

Lemon

Antiseptic, astringent and detoxifying properties

Lemon balm

Insomnia

Myrtle

Insomnia

Patchouli

Agitation, anxiety or stress

Peppermint

Exhaustion, reduced arthritic pain and spasms and memory loss

Pine

Pain management

Rosemary

Blood pressure regulation, colitis relief, constipation and indigestion symptoms and exhaustion

Sage

Muscle cramps and tension Sandalwood End-of-life

Spearmint

Fatigue

Sweet marjoram

Pain management

Tea tree

Acne, blisters, burns, cold sores, dandruff, insect bites and oily skin

Valerian

Agitation, anxiety or stress

Ylang ylang

Insomnia, antidepressive and aphrodisiac properties [32]

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Essential oils are considered to be generally safe with minimal reported side effects. Some essential oils are considered as “approved food additives” by the US Food and Drug Administration and appear on the Generally Recognized as Safe list. Adverse side effects of essential oils may include irritation of the eyes, mucous membranes and skin, and sensitization to essential oils that contain aldehydes and/or phenols. Cross-sensitization to other essential oils, foods and beverages, seasonal sensitivities and allergic reactions may also become present and require treatment. Individualized considerations should always be taken into account. Once again, healthcare professional should be first consulted before essential oils are used, especially if there is any history of reactivities to these substances.

PHEROMONES Pheromones are chemical substances that are created and emitted by organisms as odorants—often as oils or sweat—into the environment that may influence the behavior or physiology of other members of their species. This is particularly the case for mammals or insects. Pheromones may be immediate acting, slower acting or signalers. They include pheromones that are designated aggregation, alarm, epideictic, food, primal, releaser, sex, signal, territorial, trails and others (such as calming and necromones). In mammals, primer and releaser pheromones may predominate. • Aggregation Pheromones are involved in defense, mate selection and overcoming host resistance. They are generally used for pest suppression and may be ecologically selective, effective and nontoxic. • Alarm Pheromones may be released when predators attack, and they may trigger aggression or flight in animals and insects. In plants, alarm pheromones may result in tannin production by surrounding plants that decreases palatability if these plants are consumed. • Epideictic Pheromones largely mark the spots where female insects lay their eggs. • Food Pheromones tend to be linked to trail pheromones; they are connected to organisms that use volatile hydrocarbons that guide their activities toward nesting for survival. • Primal Pheromones help to trigger changes in developmental events. They tend to differ from other pheromones that primarily trigger behavioral changes. • Releaser Pheromones principally cause rapid responses in recipient behavior that are promptly reduced as opposed to primer pheromones. • Sex Pheromones signify when females are approachable for breeding, or they serve to indicate the species and genotype of males. Females produce most sex pheromones. Sex pheromones may also be involved in aggregation pheromone activities. Male-producing sex attractants may also be referred to as aggregation pheromones. • Signal Pheromones serve to create brief changes, including neurotransmitter release. • Territorial Pheromones basically mark boundaries and territorial identities. These pheromones include those that are in the urine of cats and dogs. • Trail Pheromones (see Food Pheromones). • Other Pheromones such as calming pheromones for appeasement and necromones that are indication of decomposition or death [33]. There have been some demonstrable reports in humans that exposure to body odors may elicit responses by other humans, but with few consistent and strong behavioral responses. Rather, chemical messengers may function as modulating pheromones that may affect mood or mental states. A person’s “odorprint” may also be responsible for attraction, such as between a nursing human infant and its mother. This type of odorprint may be affected by such factors as diet, the environment, genetics and/or health [34]. How do pheromones fit into the aging profile, if at all? Research has demonstrated that aging affects sexual appeal. Pheromones produced at different ages appear to change with age and affect sexual attractiveness differently. Certain hydrocarbon production may indicate fertility and health, which may wane with age. Throughout reproductive years, genes are transmitted that ensure continuity among generations. Pheromones attract desired members of species for this purpose; however, these chemicals appear to fade with age [35]. This may be one of the reasons why some people who are aging rely on perfumes with marketed pheromone effects—particularly at a period of time when their sense of smell may be decreasing. It may also be an effort to

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mask “old people smell,” the characteristic odor of elderly people that might be linked to the way that animals recognize who is young or old, or who is sick or dying. With age there is a change in human body odor, as determined by various skin gland activities, and how substances that are emitted from these glands intermingle with bacteria. When sebaceous glands secrete sebum, a waxy substance to lubricate and waterproof the skin, apocrine sweat glands discharge perspiration and eccrine sweat glands emit a clear, odorless but salty-tasting liquid. These substances along with their lipids and steroids combine and create body odor. This “old people smell” may not as intensive or offensive as the smell of younger or middle-aged men when sweating may be at its peak in relation to musculature, but it still may be distinctive to this age group. Some postulation is that it is the result of a higher level of 2-nonenal in the sweat and on the skin of older people, but this compound has also been connected with the scents of aged beer and cucumbers—two familiar and often appreciated smells. Staying clean and well hydrated, with diets devoid of alcohol, cigarettes and spicy foods may also be preventive [36].

SMELL AND HEALTH When humans become infected or sick their odors may switch from agreeable to offensive, as detected through breath, blood, skin and/or urine. The reason may be due to changes in immune activities to fight infections. In particular, the smell of urine may be affected by inflammation, and this odor may be used to distinguish between healthy and unhealthy individuals. Age, gender and health may all contribute to this unique odor, which is referred to as an “odorprint.” In turn, these subtle changes may signal the need for protection from additional infections. Or this ability might instigate an immune response in preparation for potential bacterial or viral intruders. Odorprints have been correlated with some disease states. These include baked bread and typhoid fever, raw meat and yellow fever, and stale beer and glandular disease. Cancer cells may release compounds that are unlike than those that are found in healthy cells; particularly during the earlier stages of development, but this level may be quite subtle and hardly noticeable [37]. To some people, phantosmia, the smell of something that is not present, or parosmia, a smell that is no longer appealing, may be indicative of changes in health. More common are hyposmia, or diminished smell, or anosmia, or smell loss, both described in the section on Smell Decline and Loss that follows. Changes in smell and associative diseases include differences in smell between the left and right nostrils that have been associated with early-stage-Alzheimer’s disease; diminished sense of saltiness that may be indicative of a respiratory infection or sinusitis; overall decline in a person’s sense of smell or “olfactory hallucinations” (unusually unpleasant and/or highly individualized smells such as the smell of fish when fish are not present) that may be signs of a forthcoming seizure or stroke; or unpleasant, hallucinated smells (such as burning or decomposing) that may signify premigraine sensations [38]. For these and other conditions, it is best to communicate their occurrence with a healthcare professional at their earliest signs of development.

SMELL AND OBESITY Obesity may be linked to a gene that affects appetite and a person’s sense of smell. The gene FTO on chromosome 16 is the first widespread genetic flaw to be linked to obesity. It may have a major influence on obesity and diabetes and influence appetite by influencing the brain, or altering the messages from the fat stores and other tissues [39]. There may also be differences in how thin and overweight people access food smells, particularly if they have just eaten. Overweight people with a higher inclination for food odors may have greater appetites than thinner individuals after they were fed. An explanation for this phenomenon may be that the human body has the capacity to detect and reject foods that are no longer needed to maintain the correct energy balance, but that a keener sense of smell in overweight individuals might overrule this balance [40].

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Acute loss of smell may also impact metabolic health and obesity, according to some animal studies. Laboratory animals with an inability to smell had less body fat weight than laboratory animals with intact sensory receptors. Laboratory animals without a sense of smell appeared to be protected from some consequences of higher-fat diets such as inflammation in fat tissues and insulin resistance that might ordinarily contribute to diabetes [41]. Research has demonstrated that when some humans are hungry the body releases hormones and other signals that activate the sense of smell to search out food for satiation. In some laboratory animals, it was noted that chain reactions of hormones, nerves and physiological functions that were initiated by certain food smells altered their metabolism and triggered the animals to stockpile foods for energy [42]. Also in some laboratory animals, selected food smells increased thermogenesis in their brown and inguinal fat deposits for energy. This observation indicated that some smell signals were sent to the hypothalamus in the brain where metabolism is regulated, which activated the sympathetic nervous system to burn more energy and fat. In particular, NA, a hormone and neurotransmitter, was summoned to help mobilize the brains and bodies of laboratory animals for actions that were necessary for survival. It has been speculated that the pathway between smelling food and gaining weight may be through a cranial nerve known as the vagus nerve. However, this connection is uncertain in humans and may only apply to laboratory animals in the prevention of severe weight gain and/or the facilitation of weight loss. Eventually, laboratory studies of olfaction and obesity may shed light upon issues of binge eating and food additions in humans, and provide options to invasive weight-loss surgeries. At the present, interfering with olfaction is not considered as a viable obesity treatment [43].

SMELL AND WEIGHT LOSS Smell and taste dysfunction have been implicated in unintended weight loss as well as loss of appetite that may lead to malnutrition and decreased quality of life. It has been theorized that if the sensory system is saturated by sensory overload, then decreased hunger with subsequent weight loss may ensue. The abundance of sights, smells and tastes of foods and beverages might result in the release of insulin and an increase in metabolism in the short run, but not over the long run as there may be sensory adaptations. While it may be alluring to apply laboratory animal research to humans and manipulate the sense of smell for weight-loss purposes, real concerns about olfaction-related weight-loss stem from decreased interest in foods and beverages. This disinterest may trigger such conditions as anorexia, gastrointestinal disorders such as diarrhea, nausea or stomachache, inflammation, muscle wasting and/or weakness and other circumstances. Aging people may be at higher risks due to calorie protein nutrient malnutrition. A well-balanced diet with age-appropriate servings of foods and beverages and age-designed activities continues to be a more prudent approach to weight management than sensory manipulation. The services of a geriatric-trained registered dietitian/nutritionist may be especially beneficial. Food manipulation to enhance food texture, flavor improvement and palatability, provision of dietary variety and feeding assistance where necessary may collectively be beneficial. So may environmental adaptations to help prevent social isolation and support conviviality; the evaluation of pharmacological therapies to help to identify medications that may decrease appetite and/or affect weight loss or weight gain; and medical diagnoses to evaluate and address such issues as cardiovascular diseases, dyspepsia, endocrine disorders, malabsorption syndromes, neurological causes, psychiatric disorders, respiratory diseases and/or swallowing disorders that may individually or collectively affect weight issues [44]. For more discussion on olfactory decline and weight see the following section, Smell Decline and Loss.

SMELL DISORDERS: MECHANICAL AND METABOLIC A number of factors may contribute to smell disorders that are considered to be mechanical or metabolic. Mechanical factors may include changes in the nose, changes in the nerves that lead from the nose to the brain and/or changes in the brain itself. Metabolic factors may include those that directly or indirectly affect metabolism, such as chronic alcoholism or medical treatments.

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Sections of the olfactory area or its connections to the brain may be destroyed due to head injuries in young adults and Alzheimer’s disease in older adults. With head injuries, the fibers of the olfactory nerves that connect the smell receptors to the brain may be damaged, or a fracture of the cribriform plate bone that separates the brain from the nasal cavity may occur. In Alzheimer’s disease and other degenerative brain disorders such as multiple sclerosis, the olfactory nerve may be affected or destroyed. An additional mechanical cause of smell disorders may be the common cold that may contribute to conductive olfactory loss. A cold may clog the nasal passages and prevent odors from reaching the smell receptors lodged in the mucous membrane lining of the nose. Still another temporary condition of smell loss may be the result of the influenza virus, which may interfere with or damage the olfactory epithelium; however, in most cases the sense of smell and taste may return. Allergic rhinitis, which is activated by animal hair, dust and/or pollen; chronic rhinosinusitis with inflamed nasal passages, a deviated septum; or a foreign body that obstructs airflow may also be contributing factors of conductive olfactory loss [45]. Metabolic, environmental or situational causes for smell loss may include chronic alcoholism as previously mentioned, diabetes, drug use, epilepsy, exposure to toxins, latrogenic (caused by medications or treatments), pernicious anemia (as provoked by vitamin B12 deficiency), poor kidney function, radiation, stroke, tumors, vitamin A deficiency and/or zinc deficiency.

Types of Smell Disorders Smell disorders may be evidenced as decreases in the ability to smell, changes in the manner that odors are perceived or combinations of these manifestations. Anosmia, dysosmia, hyposmia, parosmia and phantosmia are recognized smell disorders. Anosmia, a complete loss of the sense of smell, is uncommon. Some people are born without a sense of smell, a rare condition referred to as congenital anosmia. • Congenital anosmia may be an aspect of Kallmann syndrome, a condition that is characterized by delayed or absent puberty, due to a lack of hormone production by the pituitary gland from a defect in the hypothalamus. • Idiopathic anosmia may occur in people who display no apparent cause for the loss of the sense of smell after extensive testing. Hyposmia, a partial loss of the sense of smell, is more prevalent than anosmia. People who have hyposmia may be able to recognize acidic, bitter, salty and sweet substances but may not be able to discriminate among specific flavors since this ability depends on the sense of smell. Both conditions of anosmia and hyposmia may affect the enjoyment of foods and beverages, nutrient intake and health and well-being. Dysosmia, a distortion of the sense of smell, may cause some odors to smell displeasing or even offensive. Dysosmia may be due to brain infections from the herpes virus, depression, mouth infections, partial damage to the olfactory nerves, poor dental hygiene, seizures, sinus infections or viral hepatitis that may provoke nausea. Parosmia, a qualitative alteration of the normal sense of smell, may occur when familiar odors are perceived but their smells are distorted (as in unpleasant smells). Phantosmia denotes phantom smells, the capacity to smell odors when they are not necessarily present [46].

Diagnosis of Smell Impairment If a person thinks that his sense of smell may be compromised, he should contact his healthcare professional and inform them of any sensory changes and/or symptoms before taking over-the-counter medications. Some of the questions that should be asked and addressed include those given in Table 5.4. The healthcare provider should review the patient’s dietary, medical and sensory history if it is available. A physical examination of the nose and oral cavity may disclose if there are any blockages. A more thorough examination of these areas may include a computed tomography scan, a magnetic resonance scan and X-ray and/or a nasal endoscopy that uses a smell camera encased in a thin tube to better examine the nasal passages. These tests may help provide a clearer examination of the structures inside of the nose. Imaging tests may show a polyp or abnormal growth that might impede the nasal passages. They may also show if there is an abnormal growth or brain tumor responsible for altered smell. A biopsy may be warranted for additional examination and determinations.

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TABLE 5.4

159

Questions About Chemosensory Identification, Impairment and Improvement

1. Why do you think that you taste or smell differently? 2. Can you taste or smell some foods and beverages better than others, and if so, which ones? 3. Do you have seasonal allergies, a cold or the flu, or are you recovering from any of these conditions? 4. Do you take any medications and if so, which one? 5. Do you have any long-term conditions or disease states, such as cardiovascular disease, diabetes, hypertension or kidney disease? 6. Have you been diagnosed with depression, the early stages of dementia or Alzheimer’s or Parkinson’s disease? 7. Have you been experiencing any falls, or have you had any head injuries? 8. Do you have any known vitamin and/or mineral deficiencies? Do you take supplements, and if so, which ones? 9. Have you sensed any strange smells, particularly when none are present? 10. Have you experienced a strange taste in your mouth, had dental or gum issues or acid reflux? Data from https://www.dartmouth.edu/Bdons/part_1/chapter_3.html.

Smell Tests to Detect Olfactory Function A specialized healthcare provider may test for olfaction using a number of methods. To begin, he may ask a patient to close her eyes and smell a comparatively familiar odor from a vile, and then repeat the procedure with alternate nostrils. A familiar substance may be coffee grounds because they are so easily identifiable and cause little trigeminal stimulation. Both acetic acid and ammonia should not be used because they are so strong and may cause strong trigeminal stimulation. Anosmic individuals may still be able to sense these very assertive smells. A specialized healthcare provider may then be able to tell if a person cannot smell at all, or can smell somewhat and whether or not she may be able to identify what she can smell. If he cannot identify an odorant, he may be able to identify which nostril is most operative, or recognize the asymmetry of their sensitivity [3]. The UPSIT is a commercially available test for smell identification that tests a person’s olfactory system. Dr. Richard Doty, a world-renowned researcher in the field of olfactory functioning and dysfunction, invented the UPSIT test in 1983. The UPSIT test has been widely used as a self-examination tool to help diagnose diseases that include Alzheimer’s and Parkinson’s disease. The UPSIT test measures a person’s ability to detect odors at the suprathreshold level with “scratch and sniff” smell strips and a short multiple question test. In Alzheimer’s disease, odor detection and identification may both be affected. People who have Alzheimer’s disease may have trouble with this test when they perform higher olfactory tasks with specific cognitive processes. Both olfactory dysfunction and decreased cognition are Alzheimer disease correlates. A very high percentage of cases of Parkinson’s disease involve smell dysfunction that may be diagnosed by the UPSIT test. The UPSIT test may also be able to differentiate among essential tremors, progressive supranuclear palsy (Steele-Richardson-Olszewski syndrome) and/or Parkinson’s disease that may be induced by MPDP [(1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a prodrug to the neurotoxin MPP 1 , which may lead to permanent symptoms of Parkinson’s disease]. The UPSIT test may also be able to detect if other family members besides the individual who was diagnosed with Parkinson’s disease might be at risk of developing Parkinson’s disease [47]. National Geographic Smell Survey In 1986, the National Geographic magazine circulated approximately 11 million copies that included a scratch and sniff panel to test the detection and identification of the smells of androstenone (a chemical in sweat), banana, cloves, mercaptans (chemical compounds that are added to natural gas to make it easier to detect because it then smells poorly, such as garlic or rotten eggs), musk and rose. The participants were also asked to rate the intensity of the odors, pleasantness (or lack of pleasurable appeal) and other attributes. General health, handedness, olfactory problems and the use of cologne or perfume were also taken into consideration [48]. It was detected that women were more likely to have a good sense of smell before men, but that this ability may declines with age (as it does for men). Factory workers were rated above average for odor identification, while people who worked outdoors were rated below average, but they were classified more sensitive to faint odors than indoor factory workers. Office workers were graded the best among the groups that were studied for identifying odors.

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Smell perceptions differed among people in different countries. People with allergies performed better than they anticipated. A significant percentage had suffered a previous loss of smell and a slight percentage reported that they could not smell at all. Smokers were more sensitive to banana and musk odors and less sensitive to the odors of cloves, androstenone and mercaptans. Pregnant women were not as acute at smelling than nonpregnant women. As people aged they were less likely to consider the smell of escaping gas as unpleasant. Sensory scientists from the Monell Chemical Senses Center in Philadelphia conducted the research. They discovered that strong odorants have a greater likelihood to evoke vivid memories, and that the most stirring recollections were created by extremely pleasant and/or extremely unpleasant odors [49]. Since sensory scientists believe that the sense of smell is intimately connected to areas of the brain most associated with emotions and memory, the notion that strong odorants have these capabilities provides compelling options for heathcare providers and flavor manufacturers. For more discussion on this topic and speculative opportunities, see Chapter 6, Flavor Enhancement Ingredients, and Chapter 7, Flavor Enhancement Techniques.

Treatments for Smell Disorders There does not appear to be specific treatments for smell disorders. Nasal surgery may be needed to remove any obstructions. Chronic rhinosinusitis may be treatable with medical care. People with this condition may be able to regain some of their sense of smell after oral steroid treatment or steroid sprays to reduce some inflammation. Oral corticosteriods may be another option. Mild exercise, steam and/or nasal rinses may be less invasive choices to help clear the nasal passages blocked by simple colds. Smoking may damage the sense of smell, particularly if it is long-term. By quitting smoking, some sense of smell may demonstrate some improvement. Distorted smells may be treated with small dosages of antiepileptic medications since the brain may misinterpret signals at the root of these distortions. On the other hand, sometimes the reduction or elimination of medications (as warranted by a healthcare provider) may also offer some relief. The improvement of any illnesses or disease states may also provide some reinstatement of smells.

Smell Fatigue Though the human sense of smell is so easily stimulated in comparison to other basic senses, it is quite fragile. This state is referred to as “smell fatigue” and is a normal condition for people of all ages, those who are aging included. However, with aging and decreased smell, the ability to sense the origin of a smell and to continue to detect and identify it over time might be exacerbated. Smell fatigue is a component of sensory adaptation whereby individuals may adjust to a constant level of stimulus in their environment that makes them able to retain sensitivity to changes in their surroundings. Smell fatigue may be likened to the sensory adaptation of the sense of sight that allows one to adjust to a pitch-black country road or darkened theater. Smell fatigue may also be compared to the sensory adaptation of the sense of sound that helps a person adapt to the noisiness of a busy city or a bustling restaurant. Generally in healthy, younger individuals sensory adaptation is fairly short term. Adaptation, recovery and return to “normal” sensory functioning may require a few short moments. Continuous exposure to environmental odors may literally necessitate days or weeks for adaptation, recovery and return to ordinary smell sensitivity, despite removal of the problematic odor source. The aging sense of smell might also impair the speed of recovery to normalcy [50].

Smell Adaptations Since smell loss or decline has been associated with decreased food enjoyment and possible depression, the identification of chemosensory decline is of primary importance for the health and well-being of aging people. So too is the issue of domestic safety: the employment of gas detectors is critical for the protection and peace of mind of aging people and their care providers, families and friends. Improving the personal hygiene of aging people with particular attention to dentition may help to correct disagreeable smells and ensure unobstructed flow of smell molecules.

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Taking precautions to check the safety of foods and beverages in home settings may help to ensure food safety when the sense of smell wanes. This measure includes the inspection of “sell by” and “use by” dates and the practice of discarding older canned and packaged goods, condiments, seasonings and older leftovers. Frugality and food safety do not go hand-in-hand: When in doubt, even aroma-free foods and beverages should be discarded if there are any questions about their safety [51].

IMPROVING THE SENSE OF SMELL While the restoration of the sense of smell is not yet a reality, chemosensory scientists are involved with ongoing research about such topics as the associations among food preferences, dietary changes and chronic diseases in the aging; the effects of the environment on chemosensation; new diagnostic tests for chemosensory disorders, and the potential regeneration of sensory nerve cells. This research may have the capacity to assist aging people who have undergone chemosensory changes or may be doing so in the future, and to provide guidance for healthcare professionals and care providers [52]. While the restoration of the sense of smell might be considered implausible to date, steps can be taken to try to sustain the senses of smell and taste. These include those shown in Table 5.5. TABLE 5.5 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

Steps to Sustain the Sense of Smell (and Taste)

Address any known or suspected allergies. Adjust to less salt (and less sodium) and sugar, and allow the true tastes and smells of foods and beverages to surface. Attempt to remember the delights of significant foods and beverages. Avoid highly offensive odors to help prevent desensitization. Be hydrated—especially if taking medications. Chew foods slowly and thoroughly. Dine with others as much as possible to enhance eating experiences. Eat “around the plate” instead of one food at a time. Expose the olfactory receptors to a wide range of tastes and/or smells. Ensure that vitamin and mineral status is adequate. Humidify inside air to add moisture to dry environments. Investigate any pharmaceutical interactions. Keep the nasal areas clean and clear as much as possible. Meet hunger needs (instead of random eating), when the senses of taste and smell might be at their strongest. Moderate or eliminate alcohol consumption. Quit smoking to preserve olfactory receptors and nerves. Reduce the consumption of very hot or very cold foods and beverages; rather, appreciate foods and beverages at their ideal temperatures. Remain active, since the sense of smell may be heightened after activities. Serve recognizable foods and beverages so that the brain correctly registers their appearances. Stay free of head injuries by trying to prevent accidents and falls. Take a positive approach to newer smelling/tasting foods and beverages. Try “sniff” therapy to emphasize desirable smells [53].

Data from http://www.rd.com/health/wellness/sharpen-your-sense-of-smell-and-taste/.

Utilizing Smell Memory for Improving Smell Sensations Since odors play important roles in learning and memory with regard to events and places, some smells may provide cues for recalling emotional episodes. It also follows that by utilizing smell memory in positive ways, evoking happier food-centered times, these measures may encourage eating and drinking—particularly in aging people who have forgotten the “pleasures of the plate.” This is because certain smells may have been ingrained as emotional memories and may be retrieved as emotional responses in contrast to the conscious mind. This phenomenon may be most pertinent to people with forms of dementia, such as Alzheimer’s disease. One of the symptoms associated with dementia is identity loss. Certain smells may be able to trigger specific memories and their accompanying emotions, which may help to define the environments of dementia-affected individuals and their roles within them. AGING, NUTRITION AND TASTE

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The apolipoprotein E gene has been identified as a risk factor for late-onset dementia of the Alzheimer’s type. Swedish researchers have explored its association with smell and memory loss and speculated that this gene may be responsible for loss of both smell and memory. It may be possible to address the suppression of this gene or develop mechanisms to counterbalance its effects [54]. In the meantime, some of these measures might be taken: • Smell the aromas of comfort foods . . . Foods and beverages that are thought to be “comfort foods” tend to be very personal and likely vary among aging individuals with dementia. In general, comfort foods gravitate toward dishes that grandmothers or mothers prepared, such as buttered noodles, chicken soup, chocolate chip cookies or cake, mashed potatoes, oatmeal, puddings and/or other foods. Eating histories from family members or care providers may provide useful information for preparing comfort foods such as these, and for generating their reminiscent aromas. Allow time for these redolent aromas to permeate the dining environments. • Smell the aromas of “dining out” foods . . . A favorite neighborhood pancake diner, pasta restaurant or steak house might conjure memorable moments with friends or family. Preparing these foods at home or in institutional settings may help to fill the air with aromas that recall more celebratory and/or prosperous times. Do take ethic preferences into account. Aromas that are generated in Asian, Central American, Italian and other ethnic restaurants may be more profound and evocative for individuals from diverse cultures. • Smell the aromas of “childhood” foods . . . Perhaps there are favorite foods and/or beverages that are reminiscent of childhood days, such as hot dogs, grilled cheese sandwiches, macaroni and cheese, milkshakes, peanut butter and jelly sandwiches or tomato soup. Some of these items are clearly more fragrant than others—or they may be prepared with certain cooking techniques that especially bring out their aromas. Either eating histories or trial-and-error may indicate which aromas are appealing and have the potential to perk dull appetites. Many may be enhanced with other ingredients to add nutrients, others may be trimmed of calories, fats or sugars, but make sure that their aromatic qualities still remain or are elevated in the process. • Smell the aromas of “holiday” foods . . . Little compares to memorable holiday meals, such as those that might have been prepared for the Fourth of July, New Year’s Eve, Thanksgiving, religious holidays or others. A barbecue cookout, mulled wine and roasted nuts and a flavorful roast and gravy may conjure happy events with family and/or friends, along with a profusion of other filling foods and beverages. Even feelings of being “over-stuffed” may have evoked better times. By celebrating birthdays and other holidays such as these on a regular basis, and by incorporating some of the scents of these holiday-related foods and beverages, aging people with dementia may find some dining comfort. • Smell the aromas of “reward” foods . . . Less labor-intensive foods and/or beverages, such as candy, chips, chocolate, ice cream, popcorn and/or soft drinks that are often associated with good spirits and rewards, may have been common “go-to” foods and beverages during the younger years. While some of these items may be less nutritious than other choices, caloric intake may still matter. By preparing especially fragrant options that are higher in nutrients (such as freshly popped corn or warmed hot chocolate), some evocative smell memories may be aroused and calories consumed.

INTERACTIONS OF THE SENSE OF SMELL WITH OTHER SENSES The five basic senses of hearing, sight, smell, taste and touch are independent in some regard and highly collaborative in others. While each of these senses portrays the environment in which it functions from slightly different perspectives, in their entirety, they interact to provide a uniquely individualistic worldview. For example, an intact sense of sight provides visual cues, such as the advance of a car or animal. An intact sense of hearing provides “sensory crosstalk” communicating that the impending danger may be near. If either of these senses are compromised by aging, either an injury may occur, or other mechanisms may compensate.

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For example, a person may see the object nearing her before hearing it, or vice versa. Sensory compromised individuals may find that one or more of their senses plays “double duty” and counterbalances another, such as a blind person who can hear sharply, a deaf person who has keen vision or a blind and deaf individual who has a honed sense of touch. In some cases, this ability to “take on” other senses may seem to impact or stimulate any of the other senses into a sensory overload. This is called synesthesia, which is a union of the senses. In synesthesia, the cognitive pathways lead to automatic and involuntary experiences in one or multiple cognitive pathways. There is little explanation for the development of synesthesia. Nor is there strong scientific evaluation. Synesthesia may develop in childhood when children are first bombarded with a seemingly multitude of abstract concepts. This may explain why the most common forms of synesthesia have to do with color, number form and sequence. Less common forms of synesthesia include smell color, flavor color, month flavor, sound flavor and phoneme color. These perceptions may vary among individuals. Some synesthetes do not know how they perceive their environment until it becomes problematic [55]. Other than synesthesia, humans rarely experience isolated sensations. In fact, artists, musicians and poets tend to view their “worlds” simultaneously. The following senses of sight, sound, taste and touch interact with smell in a variety of respects.

Sight The normal sense of sight may be quicker than the sense of smell. The human ability to detect something visually may be less complex than that of smell, which often requires a number of sensory clues. For instance, when a person sees a common beverage such as orange juice, she may immediately know that it is bright orange, pulpy and thick, and that this usually indicates freshness. The nose requires a whiff and maybe a taste to discern if it is fresh orange juice, or if it is reconstituted or spoiled. Another example of how the sense of sight may impact the sense of smell involves the sight of an orange grove, which is replete with hundreds of brightly colored orange-filled trees. The eyes tell the viewer that the oranges are ripe for picking. This vision does not change once the oranges are picked and gathered for eating or processing. Unlike the sense of sight, the sense of smell may not identify the freshness of the oranges until they are in closer proximity, so in this instance the sense of sight is quicker, both for longer and shorter distances.

Sound The sense of sound may be captured digitally or electronically as compared to the sense of smell, which is usually captured in volatile molecules. Some research suggests that the information that is received through the nose may be transformed by noise. This implies that there might be a smell-sound sense. It seems that the olfactory tubercle at the base of the brain associated with odor detection may respond to some sounds in selected laboratory animals. When a mixture of tones and odors were sent into the tubercle cells of laboratory animals they became either enhanced or suppressed [56]. In fact, perceptual interplay between smells and sounds have been reported since the mid-1800s when French perfumerist G. W. Septimus Piesse cataloged odors that were based on analogous auditory pitches. Daniel Wesson and Donald Wilson discovered the first neural evidence for this occurrence in 2010 at the Nathan S. Kline Institute for Psychiatric Research in Orangeburg, New York. However, because sensory activity may not always equate with perceived changes, more research is needed to determine what these laboratory animals actually smelled and heard. The Wesson Wilson discovery of olfactory-auditory integration supported the notion that there may be intimate connections among sensory systems. Their work helped to clarify the “defective processing” that is related to the disorder of synesthesia: when the senses are overloaded colors may be tasted, flavors may be visualized and other often-bizarre sensory combinations may be experienced (see Interactions of Smell With Other Senses) [57].

Taste Smell and taste are known as the chemical senses since they depend on chemical transduction. Chemoreceptors respond to chemical stimuli from smell odorants and tastants, such as those from vanilla and

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sugar. When the odor and taste components of vanilla and sugar are congruent, they may be perceived as one sensation that seems to come from the oral cavity. In truth, vanilla is really tasteless. The smell of vanilla comes from the nose through the passageway between back of the nose and the back of the mouth. Incongruent tastes and smells also exist, such as vanilla and salt. People might think that they are sensing this ingredient combination in the nose, but they may actually taste this ingredient combination in the mouth. The phenomenon of sensory fatigue and adaptation with regard to smell is also operative for taste. And since the sense of taste is so intricately involved with the sense of smell, some of the fatigue and adaptation principles may overlap. For example, both astringency and bitterness may necessitate up to 90 seconds of recovery time so as not to influence the taste of wine. Sugar may also take some time to fade. Chocolate with its astringency, bitterness and sweetness tends to have a longer aftertaste and may fool the palate when tasting wine, as does some cheese [58]. Since olfaction engages a duel sensory process for perceiving odors orthonasally (via the nostrils) and retronasally (by means of the mouth), what interferes with either of these sensory processes may affect the detection and identification of odors. The issue of nasal congestion has already been discussed. Insufficient mucous production, poor chewing and/ or poorly fitted dentures or other oral conditions may hinder both gustation and orthonasal olfactory perception. Additionally, dentures that cover the palate may decrease retronasal flavor sensitivity and impede the transport of odors from the mouth to the olfactory receptors [59].

Touch Many aromas have a tactile component. In a manner of speaking, a person may be able to “feel” an aroma, such as cinnamon (spicy), spearmint (minty) or vinegar (acidy). While hot peppers, salsa and garlic are quite pungent, if a person has lost his ability to smell these foods and ingredients, he may be able to detect their bite, burn, numbing, pain, prickle or tingle. The same may be true for citrus slices with their astringency and pucker; ice cream, coffee and tea with their respective cooling and warming capabilities; butter and cream with their fullness and slipperiness; and crackers and popcorn with their crackling and jagged characteristics. These sensations and others fall into the classification of somesthesis, which is considered as the faculty of bodily perception. Somesthesis is responsible for the sense of touch (coldness and warmness, itchiness, pain and pressure), along with movement and positioning. One is graphically able to feel these sensations and to smell the foods and beverages that they simultaneously evoke. This is why the senses of touch and smell are so interwoven [60]. The skin is also known to have olfactory receptors that are postulated to have nonolfactory, ancestral function in epithelial biology. Likewise, olfactory sensors are also found in the blood, heart, lungs and sperm to help to locate eggs [61].

CHALLENGING ASSUMPTIONS ABOUT CHEMOSENSORY CHANGES WITH AGING While much has been speculated about chemosensory decline with aging, there is no consensus and challenges still remain. Some of these challenges may include the following considerations : • Do some taste(s) decline earlier than others, and if so, in what order and does this order matter? • How are changes in olfaction verified when there are so many smells and odors to detect and to identify? • Are aging people at heightened nutritional risks due to their reported chemosensory decline, or are medical conditions, diseases, medications and the aging process collectively responsible? • Can nutrition guidelines be accurately formulated when aging people demonstrate great variability in the many factors that comprise the aging process—chemosensory changes being just one facet? While an independent effect of aging on the chemical senses has been established, chemosensory changes due to aging appear to be decidedly variable among individuals and across diverse stimuli [62]. Additional discussion can be found in Chapter 8, Meeting Nutritional and Disease-Specific Needs of Aging.

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DIGEST Human beings may be less dependent upon their sense of smell as bears, elephants, kiwi birds, moths, sharks or snakes. When the brain’s olfactory lobes are measured and smell receptors are counted in these species they highly rate in number, and much more so than in some humans. The scent receptors in black bears may be highly activated for distant food. Grizzlies and polar bears may be able to smell through ice—not only for food, but also for sexual attraction. African and Asian elephants are known to have a superior sense of remote smell, particularly in the water for drinking and bathing. New Zealand kiwi birds are said to have a superior sense of smell since they are flightless and must scavenge for food on the ground. The male silkmoth relies upon its ultra-sense of smell for mating. Some sensory scientists are studying the silkmoth as a model for scent-detecting robots. The great white shark reportedly has the largest olfactory bulb of fellow sharks, but it may not foster a better smelling potential. Rather, it may contribute to the great white shark’s water movement and electromagnetics. Snakes do not use their noses to smell. Instead, they “taste the air” to capture scent particles, and they use a specialized organ in their mouths that is referred to as Jacobson’s organ for sensing food and/or danger [63]. These remarkable creatures are capable of an acuteness and diversity in their sense of smell that exceeds that of humans, and yet their milieu is so much different. They need to travel miles to seek and find their food sources, and all that humans need to do is travel to the nearest cupboard, refrigerator, market or restaurant. If and when the sense of smell changes in humans, they may be able to discover compensatory measures to help improve their conditions. By understanding the sense of smell as described in this chapter, aging people and their care providers, families and friends may be better equipped to address some olfactory changes that develop as the years progress. Unlike bears, elephants, kiwi birds, moths, sharks or snakes and other animals with their smell acuity, humans may be better able to improve their olfactory situations, procurement of sensory-satisfying food sources, nutritive intake, health and well-being—and for a potentially longer lifespan!

MANNER OF SPEAKING Acetylcholine Adenosine Triphosphate (ATP) Energy Adenylyl Cyclase (AC)

Aggregation Pheromones

Alarm Pheromones Amygdala

Androstenone

Anosmia Apocrine Sweat Glands

Aroma

compound that functions as a neurotransmitter throughout the CNS primary carrier of energy in cells; able to store and transport chemical energy within cells enzyme that synthesizes cAMP (or cyclic AMP) from adenosine triphosphate (or ATP) to help regulate a wide variety of cellular processes semiochemicals that play key roles in insects for defense against predators, mate selection, overcoming host resistance and other social behaviors chemical signals that are produced by insects and some animals in response to danger unevenly almond-shaped mass of gray matter in the interior of each cerebral hemisphere; involved with experiencing emotions steroidal pheromone found in boar’s saliva, celery cytoplasm and truffle fungus; produced by fresh male sweat that might be attractive to females partial or total loss of the sense of smell; caused by blockage of the nose, head injury, infection or other causes glands that are associated with the presence of hair in human beings; secrete a concentrated fatty sweat into the gland tube; stimulated by emotional stress distinct, typically pleasant smell as opposed to odor

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Aromatherapy

Behavioral and Psychological Symptoms of Dementia (BPSD) (also known as Neuropsychiatric Symptoms) Calming Pheromones cAMP

Central Nervous System (CNS)

Chemical Aromas Chemoreceptive Sensory Interaction Chemoreceptors Cilia

Computed Tomography (CT) Scan

Congenital Anosmia

Cognition Conductive Olfactory Loss

Cork Taint Decayed Aromas Degenerative Neuropsychiatric Disorders

Dysosmia Eccrine Sweat Glands Epideictic Pheromones Expectation Assimilation

Explicit Memory (also known as declarative memory) Fragrant Aromas Fruity (Noncitrus) Aromas

FTO on Chromosome 16

alternative medical practice that uses aromatic plant oils and plant materials to balance, harmonize and promote body, mind and spirit individual symptoms in dementia patients; include agitation, apathy, anxiety, depression and/or irritability chemical signals that help to reduce excitable behaviors cAMP; a chemical messenger that is vital to many biological processes that include hormones, ion channels and proteins integral part of the nervous system of the body that consists of the brain and spinal cord; integrates information and coordinates and influences body activities generally odorous synthetic aromas; often used as fragrances specialized sensory interaction that responds to chemical substance(s) and generates biological signal(s) sensory cells or organs that react to chemical stimuli short, hair like, numerous filaments; found in lining of the trachea (windpipe) that help remove mucus and dirt from various tissues and other movements scan composed of many X-ray measurements taken from different angles; produces cross-sectional images of blood vessels, bones and/or soft tissues condition whereby people are born with a lifelong inability to smell; may be an isolated abnormality or due to a specific genetic disorder mental action or process of obtaining knowledge and comprehending through experiences, senses and thought loss that causes sufficient airway obstruction in the nose; prevents odorant molecules from contacting the olfactory epithelium fault in wine due to undesirable smells or tastes; spoilage detected after aging, bottling and opening putrid or sickening aromas or smells; include those from burnt rubber, household gas, sewage and/or sulfuric acid mental disorders with a marked decline in cognitive ability; typically attributed to CNS disorders such as Alzheimer’s, dementia and/or Parkinson’s disease smell disorder; related to distortion or qualitative alteration of smell perception major sweat glands of the human body found in skin; highest density in the palms of the hands and the soles of the feet substances that are typically used by insects to mark territories notion that taste perceptions are biased by the imagination, and if a food is expected to taste good, then it will; expectation assimilation also works in the opposite direction a major subdivision of long-term memory; requires conscious thought aromas described for cologne or perfume: floral, flowery, grassy, intoxicating, herbal, light, natural or rosy fresh and light aromas; connected with bananas, peaches, strawberries or vanilla, and fragrances with similar ingredients or scent profiles enzyme that is encoded by the FTO gene (fat mass and obesity-associated)

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MANNER OF SPEAKING

Glomeruli G protein Habituation

Hippocampus Human Chorionic Gonadotropin (hCG)

Hyposmia Hypothalamus

Idiopathic Anosmia Implicit Memory (also called unconscious memory) Kallmann Syndrome

Latrogenic Lemon Aroma Mercaptans (also known as methanethiol) Minty/peppermint Aroma Motivation

Necromones Limbic System

Magnetic Resonance (MRI) Scan

MPDP ((1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) Nasal Endoscopy

Neo-Cortex

Neuro-Vegetative Areas Norepinephrine (NE) (also known as noradrenaline [NA]) Odor

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cluster of nerve endings, small blood vessels or spores proteins that bind to the guanine nucleotides GDP and GTP; important signal transducing molecules in cells type of learning whereby organisms decrease or cease stimuli responses to stimuli after repeated or prolonged appearances region of the brain that plays a vital role in short and longterm and special memory, responsible for navigation glycoprotein hormone that is secreted by the placenta after an egg is implanted; maintains corpus luteum function and stimulate placental progesterone impaired ability to smell and/or detect odors area of the forebrain that is below the thalamus; coordinate the automatic nervous system and pituitary gland activities (body temperature, hunger, thirst and other functions) loss of smell with no apparent origin one of two major types of long-term memory; may affect thoughts and/or behaviors condition that is characterized by delayed or absent puberty; due to a lack of hormone production by the pituitary gland from a defect in the hypothalamus effect on person due to medical care, medications or treatments popular aroma in both the food and beverage and fragrance domains; connotes freshness harmless and pungent smelling gas; smells like rotting food or smelly clothes aroma described as cool, exhilarating and/or spicy; connotes cleanliness and freshness rationale for particular behavior; involved in the translation of sensory information from the neo-cortex into incentives that translate into behaviors pheromones given off by a deceased and/or decomposing organism; consists of linoleic and oleic acids multifaceted system of brain structures that include nerves and networks located on both sides of the thalamus; involved with behavior, emotion, long-term memory, motivation and other functions noninvasive medical exam that utilizes electric field gradients, radio waves and strong magnetic fields to produce images of body organs prodrug to the neurotoxin MPP 1 ; causes permanent symptoms of Parkinson’s disease procedure that uses a thin, rigid tube with fiberoptic cables for light to diagnose nasal mucosa, nasal pathology and/or sinonasal anatomy section of the brain that is involved with higher-brain functioning; involved with cognition, language, motor commands, sensory perception and/or special reasoning areas of innervation of the internal organs by the autonomic nervous system; necessary to maintain life organic chemical that functions as a hormone and neurotransmitter in the brain and body distinct and often unpleasant smell; may cause lingering feelings, impressions and/or qualities

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Odorants Odorprint Olfaction Olfactory Adaptation (also known as odor or olfactory fatigue) Olfactory Blind Spot Olfactory Cognition Olfactory Epithelium Olfactory Hallucinations (also known as phantosmia) Olfactory Receptor Neurons (ORN) (also known as olfactory sensory neurons [OSN]) Orthonasal Smell or Olfaction Orthonasally Parosmia Phantosmia Pheromones Piriform Cortex (also known as pyriform cortex) Popcorn Aroma Primal Pheromones Primary Cilium Progressive Supranuclear Palsy (also known as Steele-Richardson-Olszewski Syndrome) Pseudogenes Pungent Aromas Releaser Pheromones Retronasal Smell Retronasally Rhinosinusitis (also known as sinusitis)

Scent Sebum

Sensory Neurons Sensory Receptors

substances that evoke distinctive smells body odors that proposedly provide a consistent imprint, such as a fingerprint or DNA sample sense of smell; the action or ability of the sense of smelling the temporary inability to differentiate a particular odor after lengthy exposure denotes an odorant that cannot be detected; a specific anosmia that is likely inherited cognitive processing (acquired knowledge and understanding) of the sense of smell specialized epithelial tissue inside that is located inside of the nasal cavity; involved in the sense of smell the detection of smells by one or both nostrils that are not present a transduction cell in the olfactory system; serve the conversion of odorant information perception of odors that occurs during sniffing act of smelling by sniffing odorants olfactory dysfunction; typified by an inability of the brain to correctly identify the natural smell of an odor phantom smell or olfactory hallucination; an odor that is not truly present chemical substances that are produced and released by animals; affect behavior, especially of other species region of brain in the cerebrum that is connected to the sense of smell distinctive aroma described as the scent of popcorn; usually implies pleasant memories, often from childhood chemical substances that trigger changes in developmental events as opposed to behavioral changes solitary and apparently nonfunctional cilia of cellular surfaces uncommon brain disorder that manifests in balance, eye movement and walking disorders segments of chromosomes that are imperfect reproductions of functional genes smell with a sharp or strong aroma or sensation that is often unpleasant chemical substances that evoke modifications in the behavior of recipients smell or olfaction through the mouth; emanates from the oral cavity during eating and drinking posterior from the oral cavity to the back of the nose a condition whereby the mucous membranes of the nose and sinuses become inflamed; may be caused by allergies or infections distinctive smell; usually connotes pleasantness oily, waxy secretion by the sebaceous glands; composed of metabolites of fat-producing cells, squalene, triglycerides, wax esters and other substances nerve cells in the CNS; responsible for translating external stimuli into internal electrical impulses specialized dendrites of sensory neurons; detect specific types of stimuli such as chemicals, light, mechanical forces, temperature and others

AGING, NUTRITION AND TASTE

REFERENCES

Sex Pheromones

Signal Pheromones Smell Fatigue (also known as olfactory fatigue or odor fatigue) Smell Receptor OR7D4

Smell Training

Somesthesis

Specific Anosmia Suprathreshold Level Sweet Aromas

Synesthesia

TCA (2,4,6-trichloroanisole) Territorial Pheromones Thalamus

Trail Pheromones Transmembrane Proteins (TP) University of Pennsylvania Smell Identification Test (UPSIT) Vagus Nerve Woody/Resinous Aromas

169

chemical substances that are released by organisms to attract the opposite sex, for mating, or actions related to sexual reproduction chemical substances that trigger social responses in members of the same species a temporary and normal incapability to distinguish a certain odor protein that is encoded by the OR7D4 gene; intermingles with odor molecules in the nose; originates a neuronal response that initiates smell perception instruction or reinstruction of smells; generally for people who are recovering from upper respiratory tract infections; may be useful for brain injuries and/or other forms of smell impairment faculty of bodily perception; involves various sensory systems such as the skin and internal organs; responsible for sensations such as itch, pain, touch-pressure, warmthcoldness and movement-positioning inability to perceive a specific odor while olfactory perception is otherwise whole stimulus that is significant enough in scale to provoke an action potential in excitable cells aromas that include almond, chocolate, malty and vanilla scents; also capture the sweetness in very ripe and fragrant fruits production of a sense impression by one part of the body, or sensory or cognitive pathway through the stimulation of another part of the body chemical substance known as “cork taint” that is common to “corky” wines chemical substances that denote the boundaries and identities of the territories of organisms for survival either of the two masses of gray matter that lies between the cerebral hemispheres; relays sensory information and pain perception semiochemicals secreted by organisms that affect the behaviors of other organisms; commonly used by insects entirety of membranes; function to allow the transference of certain substances across membranes smell identification test that examines the functionality of the olfactory system tenth cranial nerve or CN X; mixes with the parasympathetic control of the digestive tract, heart and lungs aromas that are reminiscent of the scent of nature; include burnt, earthy, exotic, green, heavy, tobacco, moldy, musky, musty, Oriental, smoky and woody smells and others.

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