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Is there a correlation between hippocampus and amygdala volume and olfactory function in healthy subjects?
NeuroImage 59 (2012) 1052–1057
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Is there a correlation between hippocampus and amygdala volume and olfactory function in healthy subjects? M. Smitka a, S. Puschmann b, D. Buschhueter b, J.C. Gerber c, M. Witt e, N. Honeycutt f, N. Abolmaali d, T. Hummel b,⁎ a
Department of Pediatrics, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany Department of Otorhinolaryngology, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany Department of Neuroradiology, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany d OncoRray & Institute and Policlinic for Diagnostic Radiology, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany e Department of Anatomy, University of Rostock, Gertrudenstr. 9, 18 057 Rostock, Germany f Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, 600 N. Wolfe St., Phipps 311, Baltimore, MD 21287, USA b c
a r t i c l e
i n f o
Article history: Received 15 April 2011 Revised 11 August 2011 Accepted 13 September 2011 Available online 24 September 2011 Keywords: Smell Nose Olfaction Brain Volumetry
a b s t r a c t Both amygdala (AG) and hippocampus (HC) are integral parts of the olfactory system. The present study, including a large number of healthy subjects, was performed to compare HC and AG volumes, measured by manual tracing, in relation to specific olfactory functions, including odor threshold, discrimination, identification, and odor memory tasks. It also aimed to provide age-related normative data about the volume of the HC and AG. A total of 117 healthy volunteers participated (age range 19–77 years, mean age 37 years; 62 women, 55 men). Using the “Sniffin' Sticks”, subjects received lateralized tests for odor threshold, and odor discrimination. In addition, an odor memory and an odor identification task were performed bilaterally. A Mini-MentalState test excluded dementia. MR scans were performed using a 1.5 T scanner for later manual volumetric measurements. Volumetric measurements exhibited a good reproducibility. The average volume for the right HC was 3.29 cm 3 (SD 0.47), for the left HC it was 3.15 cm 3 (SD 0.47). The average right AG had a volume of 1.60 cm 3 (SD 0.31), left 1.59 cm 3 (SD 0.3). Increasing age was accompanied by a decrease of HC and AG volumes, which were much more pronounced for the right compared to the left side. Only the volume of the right HC showed a small but significant correlation with odor threshold (r117 = 0.21; p = 0.02). Importantly, this correlation was not mediated by age as indicated by the significant partial correlation when controlling for age (r114 = 0.18; p = 0.049). In conclusion, the present data obtained in a relatively large group of subjects demonstrates a small correlation between the volume of the HC, as an integral part of the olfactory system, and smell function. In addition, these data can be used as the basis for normative values of HC and AG volumes, separately for men, women and different age groups. This is of potential interest in diseases with acute or chronic impairment of olfactory function, in metabolic or neurodegenerative diseases or in disorders with damage of areas involved in adult neurogenesis. © 2011 Elsevier Inc. All rights reserved.
Introduction In the adult mammal brain production of new neurons is almost limited to two particular regions, the hippocampus (HC) and the subventricular zone (Amrein and Lipp, 2009; Eriksson et al., 1998; Lee and Son, 2009). Concerning the latter, neurons derive from the walls of the lateral ventricles and migrate to the olfactory bulb (OB) (for a schematic representation of the olfactory system see Fig. 1). This has
⁎ Corresponding author. Fax: + 49 351 458 4326. E-mail address: [email protected] (T. Hummel). 1053-8119/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2011.09.024
been shown in animals and in humans (Curtis et al., 2007). The OB, which is the first relay station in the olfactory pathway, remains highly plastic throughout adult life. This has been shown by animal studies with olfactory deprivation. These animals had a reduction in OB volume due to the decreased number of cells (Cummings et al., 1997; Korol and Brunjes, 1992). In humans a significant correlation between OB volumes in relation to olfactory function was observed. This was shown to be independent of the subjects' age, although OB volumes decreased with age (Buschhüter et al., 2008; Yousem et al., 1997). Other neurons proliferate in the subgranular layer and differentiate into dentate gyrus cells of the HC. The hippocampal formation plays a prominent role in learning and memory, in spatial navigation
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definition of the anterior pole boundaries of 1.63 cm 3. The volume was measured using planimetry based on Nissl-stained serial sections (Brabec et al., 2010). The present study, including a large number of healthy subjects, was performed to compare HC and AG volumes, measured by manual tracing, in relation to specific olfactory functions. It also aimed to provide age-related normative data about the volumes of the HC and AG. These normative data for different decades of life would be necessary to realize the idea of volumetry of the HC and the AG as a tool which may help to assess stage and course of diseases associated with olfactory loss. Materials and methods Volunteers and study design
Fig. 1. Schematic diagram of the major olfactory pathways. Regions in gray together represent the primary olfactory cortex. Projections between the olfactory bulb and most areas of the primary olfactory cortex are bidirectional, with the exception of the anterior perforated substance (OTu). Similarly, associational connections between the primary olfactory cortex subregions are reciprocal, apart from OTu. The downstream targets of the primary olfactory cortex represent some of the major projection sites (bottom of figure), many of which provide feedback to the primary olfactory cortex (not shown), but these connections are not meant to be comprehensive or all-inclusive. While broadly illustrative of the human olfactory system, this diagram is largely based on information obtained from animal models, due to the scarcity of human data. ACo = anterior cortical nucleus of the amygdala; aINS = agranular insula; BLA = basolateral nucleus of the amygdala; EC = entorhinal cortex; HPC = hippocampus; HYP = hypothalamus; MD = mediodorsal thalamus; PAC = periamygdaloid cortex; PIR = piriform cortex; PR = perirhinal cortex; VP = ventral pallidum; VS = ventral striatum. Figure and legend from Gottfried, J. in Hummel T, Welge-Lüssen A (eds): Taste and Smell. An Update. Adv Otorhinolaryngol 2006, vol 63, pp 44–69; with kind permission from S. KArger AG, Basel, Switzerland.
and control of attention (Sahay and Hen, 2007). It is not an integral part of the primary olfactory cortex, but it receives strong afferent input from the entorhinal cortex. In contrast, the neighboring amygdalae (AG) are part of the primary olfactory cortex (Gottfried et al., 2002). The size and structural plasticity of HC and AG have been previously studied in patients with Alzheimer dementia (Barnes et al., 2009; Horínek et al., 2007; Teipel et al., 2008), in temporal lobe epilepsy (Akhondi-Asl et al., 2011; Mechanic-Hamilton et al., 2009; Pardoe et al., 2009; Scorzin et al., 2008), in multiple sclerosis (Anderson et al., 2010), in schizophrenia (Klaer et al., 2010; Teipel et al., 2010), in aphasia after middle cerebral artery stroke (Meinzer et al., 2010), in autism spectrum disorder (Zeegers et al., 2009), in depression (Tae et al., 2008; van Eijndhoven et al., 2009), in acute psychosis (Velakoulis et al., 2006), in patients with bipolar disorder (Doty et al., 2008), and also in subjects with olfactory loss (Yousem et al., 1996a, 1996b). However, these studies included either only a small control group or no controls at all. Most studies use automated volumetric measurements (e.g. FreeSurfer, Individual Brain Atlases using Statistical Parametric Mapping) or auto-assisted manual tracings. The results in these studies displayed significant variations in terms of volume. For example AG volumes were published ranging from 1.15 cm 3 on the left side and 1.16 cm 3 on the right side (Pruessner et al., 2000) to 3.34 cm 3 on the left side and 3.44 cm 3 on the right side (Watson et al., 1992). Studies showing smaller volumes of the AG (between 1 and 2 cm 3) are supported by an anatomical study which showed an average size of the classic AG of 1.24 cm 3 and in the AG with another
A total of 117 randomly selected, subjectively normosmic individuals (55 men and 62 women), aged 19 to 79 years (mean ± standard deviation = 37 ± 17 years), participated in this study. The investigations were performed in accordance to the Declaration of Helsinki on Biomedical Studies Involving Human Subjects (World Medical Association, 1997). The study design was approved by the University of Dresden Medical Faculty Ethics Review Board (number EK 239112006). All subjects provided written informed consent for the study aims and procedures and attended our Smell and Taste Clinic for detailed diagnostic evaluation. All participants received an otorhinolaryngological investigation including a volumetric MRI scan of the entire brain, and detailed lateralized olfactory tests. In addition, subjects received an extensive review of their clinical histories in order to exclude a possible cause of smell dysfunction. In particular medical history included otorhinolaryngological, neurological and psychiatric disorders. Chronic rhinosinusitis was excluded by medical history and MR-images. Furthermore, all subjects underwent a mini mental state examination (MMSE) to screen systematically for possible cognitive impairment. Subjects were recruited by flyers at the associated university and “mouth to mouth propaganda”. Handedness was not used as a selection criteria, as normative values should be obtained in the general population. Olfactory testing Psychophysical testing of olfactory function was performed with the validated “Sniffin' Sticks” test (Hummel et al., 1997; Kobal et al., 2000). Olfactory testing comprised three tests, namely tests for odor threshold, odor discrimination and odor identification. To prevent visual cues during the assessment of odor thresholds and odor discrimination, subjects were blindfolded with a sleeping mask. Results from olfactory testing can be analyzed separately from each other. Overall olfactory function is expressed as the sum of the scores from the 3 individual tests (Wolfensberger et al., 2000). Magnetic resonance imaging All examinations were performed at a 1.5-Tesla magnetic resonance imaging system (Magnetom Sonata; Siemens, Erlangen, Germany) using the 8-channel cp-head coil. Volumes of the right and left HC and AG were determined using the MRI scans of the brain and a standardized protocol for HC and AG analysis. The protocol included: 1) 5mm-thick standard T2-weighted fast spin-echo images covering the whole brain without interslice gap to rule out any organic brain disorders; and 2) 1-mm-thick T1-weighted fast spin-echo images without interslice gap in the sagittal plane. Nine MRI datasets were of good quality, sufficient for data analysis; 108 MRI datasets were of excellent quality. MRI-sequences of minor quality were repeated immediately during assessment. To additionally investigate the reliability, volumetric measurements of the right and left HC and AG were performed by two
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independent observers, blinded to the olfactory test results, by manual segmentation using the AMIRA 3D visualization and modeling system (Visage Imaging, Carlsbad, USA). The segmentation protocol applied the anatomical boundaries that were proposed by Pruessner et al., 2000, and adapted to the actual software and datasets. Analysis was performed on sagittal, coronal and horizontal images. After completion of the planimetric manual contouring all images were reviewed and refined before calculation of volumes was carried out. Manual contouring of the HC started on the sagittal plane, beginning laterally. Tube-shaped gray matter spreads out within the inferior horn of the lateral ventricle. The medial boundaries are defined by the ventricle. The choroid plexus needs to be excluded from the measurements (Malykhin et al., 2007). The inferior and dorsal borders are identified by transition of gray to white matter. The frontomedial demarcation to the AG is built by the alveus. The coronal planes are examined next, beginning anteriorly and moving posteriorly. The inferior borders are clearly perceptible by the mostly triangular form of white matter. The HC can be discriminated against the superior localized AG. The lateral, anterior and superior borders of the hippocampal head is identified by the uncal recess of the inferior horn of the lateral ventricle. Body and tail of the HC are limited medially by white matter and laterally by the ventricle. The HC is followed to the point where gray matter is seen inferomedially from the collateral
trigone of the lateral ventricle (Killiany et al., 2005). As next step the horizontal planes are examined. These are helpful in defining the anterior and medial borders. Anteriorly the HC exhibits an S-shaped form and is defined by the AG. The olive-shaped AG is located superior and anterior to the head of the HC (Fig. 2). Volumetric measurement of the AG starts in the sagittal planes. In the inferior horn of the lateral ventricle anterosuperiorly of the HC a bean-shaped mass of gray matter is followed medially, where it grows in size. This mass is only in parts clearly defined by white matter and cerebrospinal fluid. Anterosuperiorly a thin layer of white mater defines the border to the periamygdaloid cortex. The coronal planes are followed from posterior to anterior, starting where gray matter is first localized above the alveus (Pruessner et al., 2000). Medially the AG is defined by the HC, laterally by white matter and gray matter of the caudate nucleus, which is not included (Malykhin et al., 2007). Anteromedially the AG is separated from the entorhinal cortex by a thin layer of white matter (Convit et al., 1999). In the horizontal planes the medial border is defined by the by the ambient cistern postero-superiorly. Whole brain volumes were calculated after contouring on 5-mmthick coronal planes, beginning anteriorly. The assessment was based on T2-weighted fast spin-echo images covering the whole brain without interslice gap. Subarachnoid and ventricular CSF was excluded from intracranial volume. In a first step an automatic
Fig. 2. Example for measurement of HC in the inferior horn of the lateral ventricle (dark border) and the olive-shaped AG which is located antero-superiorly to the HC (bright border), using AMIRA 3D visualization software (Visage Imaging GmbH, Berlin, Germany). The borders were defined manually on each slide in every direction (sagittal, coronal, horizontal). AMIRA allows a 3-dimensional reconstruction of the examined structures by co-registration of the borders in all three planes.
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segmentation procedure, implemented in AMIRA software was used. In a second step borders were manually redefined. Statistical analysis All statistics were performed using SPSS software version 15.0 (SPSS Inc., Chicago, IL, USA). Correlations according to Pearson were computed between volumetric measurements of the HC and AG and functional measurements. In addition, partial correlations controlling for age were performed. The level of significance was set at 0.05.
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left-sided volumes of HC and AG exhibited only a tendency towards a significant correlation (HC: r117 = −0.17, p = 0.076; AG: r117 = −0.16, p = 0.085) while the correlation was much stronger for the right side (HC: r117 = − 0.28, p = 0.003; AG: r117 = − 0.23, p = 0.014). Correlation with olfactory function Only the right HC showed a small but significant correlation between olfactory function (threshold) and volume (r117 = 0.21; p = 0.02) (Fig. 3). This correlation was not mediated by age as indicated by the significant partial correlation when controlling for age (r114 = 0.18; p = 0.049). Such correlations were not seen in the AG.
Results Olfactory function Volumetric measures of HC and AG Interindividual variations in AG and HC volumes were relatively large, ranging from 2.09 cm 3 to 4.49 cm 3 for right HC volumes and from 1.8 cm 3 to 4.45 cm 3 for left HC volumes. The volumes for the right AG ranged from 0.21 cm 3 to 2.67 cm 3 and for the left AG from 0.97 to 2.75 cm 3. Mean volumes for the entire brain were 1270 cm 3 for women (SD 113.44) and 1445 cm 3 for men (SD 122.26). In contrast, intraindividual variation was relatively small (correlation between left-sided and right-sided HC volumes: r117 = 0.79, p b 0.001); correlation between left-sided and right-sided AG volumes: r117 = 0.78, p b 0.001). The maximum intraindividual difference between left-sided and right-sided HC volumes was 0.77 cm 3 for men and 0.73 cm 3 for women, between left-sided and right-sided AG volumes was 0.79 cm 3 for men and 0.45 cm 3 for women. Side differences Mean volume of the right HC was 3.29 cm 3 (SD 0.47), mean volume of the left HC was 3.15 cm 3 (SD 0.47; p b 0.001). Such differences were not seen in the AG (right AG: 1.60 cm 3; SD 0.31; left AG: 1.59 cm 3; SD 0.3; p = 0.42). Sex differences On average, HC and AG volumes of men (HC right: 3.34 cm 3; SD 0.47; HC left: 3.2 cm 3; SD 0.47; AG right: 1.66 cm 3; SD 0.34; AG left: 1.66 cm 3; SD 0.31) were found to be larger than those of women (HC right: 3.25 mm 3; SD 0.47; HC left: 3.1 cm 3; SD 0.46; AG right: 1.55 cm 3; SD 0.26; AG left: 1.52 cm 3; SD 0.27). However, this was only significant for AG (p = 0.016) but not for HC (0.24). Age differences Left and right HC and AG volumes were relatively stable up to the 4th decade of life and declined in the 6th and 7th decades. However,
Average TDI scores for olfactory function were 33.7 (SD 3.4; range 24.8–42.1). Side differences Odor discrimination tended to be better on the right compared to the left side (p = 0.082). However, no such differences were found for odor identification (p = 0.25). Sex differences Women significantly outperformed men in terms of odor thresholds (p = 0.036), but not in odor discrimination (p = 0.11), odor identification (p = 0.74), or odor memory (p = 0.97). Age differences Odor memory decreased significantly with advancing age (r117 =0.28, p=0.002). Furthermore, odor discrimination was found to decrease on left and right sides (left: r117 =−0.35, pb 0.001; right: r117 =−0.23, p=0.015) while odor threshold decreased only on the left side (left: r117 =−0.31, p=0.001; right: r117 =−0.13, p=0.16). Odor identification scores did not correlate with age (r117 =−0.10, p=0.27). Volumetric measures — normative values A normal HC or AG volume was defined to be above the 10th percentile of the distribution of volumes within the investigated population. Thus, the following normative data arose from the current dataset: for men b45 years (n = 31) the HC should have a minimum volume of 2.99 cm 3; and for men N45 years (n = 24) the HC should have a minimum volume of 2.57 cm 3. The volume of the AG for men b45 years should be greater than 1.52 cm 3 and for men N45 years the volume of the AG the minimum volume is 1.36 cm 3. For women b45 years of age (n = 35) the volume of the HC should
Fig. 3. Relationship between the volumes of HC (in ccm) and phenyl ethyl alcohol odor thresholds (in dilution steps). In general, higher sensitivity is related to larger volumes of the HC. However, this was only significant for right-sided measures (r117 = 0.21, p = 0.02).
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have a minimum volume of 2.76 cm 3, and for women N45 years (n = 27) the volume should be at least 2.66 cm 3. The volume of the AG for women b45 years should be greater than 1.34 cm 3, and for women N45 years the volume of the AG should exceed 1.18 cm 3. The mean total volume for women of the HC for men b45 years of age was 6.44 cm 3 (SD 0.94), the mean total volume of the AG was 3.16 cm 3 (SD 0.55). For women N45 years the mean total volume of the HC was 6.22 cm 3 (SD 0.83; reduction in size of 4%), the mean total volume of the AG was 2.96 cm 3 (SD 0.41; reduction in size of 6.4%). The mean total volume for men of the HC for men b45 years of age was 6.78 cm 3 (SD 0.75), the mean total volume of the AG was 3.43 cm 3 (SD 0.52). For men N45 years the mean total volume of the HC was 6.23 cm 3 (SD 0.95; reduction in size of 8.2%), the mean total volume of the AG was 3.19 cm 3 (SD 0.7; reduction in size of 7%). Overall this means a reduction in size of the HC and AG on average of approximately 6%. This is comparable with the reduction in size of the whole brain for the volunteers b45 years from 1394.4 cm 3 to 1296.8 cm 3 in volunteers N45 years (reduction in size of 7%). Discussion In agreement with previous research the data in the present study confirmed the range of HC and AG volumes measured by volumetric MRI-analysis from other groups and by anatomical studies (Brabec et al., 2010; Pruessner et al., 2000). The volume of the HC was in excellent accordance with other authors (Pruessner et al., 2000). Local adaptations of the proposed protocol had no major influence on the overall results. This is strong support for applying the protocol as guideline for measurements of the HC. In contrast to the HC there is a discrepancy for AG volumes compared with the study by Pruessner et al. Results can be influenced by differences in the MRI-scanner, different acquisition techniques, sample size and population or adaptations of the segmentation-protocol. Above that the definition of the AG as stated by Brabec et al has a significant influence on the volumes. As the average volume in a study using planimetry of Nisslstained serial sections for the classic AG was 1.24 cm3, the average volume for the AG with wider borders was 1.63 cm3. This included the area of more diffusely scattered cells under the anterior pole of the amygdale, the area praeamygdalaris, and the sublenticular part of the extended amygdale as it continues to the substantia innominata under the globus pallidus (Brabec et al., 2010). As interindividual variations in AG and HC volumes were relatively large, small sample size numbers can have a strong influence on the overall results. This study enhances the aforementioned studies by applying manual segmentation on a relatively large number of 117 1.5T-MRI datasets by two blinded observers, therefore enhancing statistical power. The observed side differences for HC volumes with larger volumes in the right hemisphere are in accordance with most studies on HC volumetry (Pruessner et al., 2000). As the HC is an integral part of different functional circuits and has a wide range of functions a definitive cause for this observation remains unknown. There is accumulating evidence on the basis of psychophysical, clinical, electrophysiological, and imaging studies that, in general, the right hemisphere is more important to the sense of smell than the left hemisphere (Fulbright et al., 1998; Hummel et al., 1995; Sobel et al., 1999; Yousem et al., 1999; Zatorre et al., 1992). This might contribute to the frequently reported side differences of the HC. There was a significant correlation between the size of the HC and AG and the age of the volunteers, independent of sex. In contrast to the present study other groups studying the expression of sex differences in the human olfactory system found significant gender differences of AG and HC (Garcia-Falgueras et al., 2006). Garcia-Falgueras et al. used VBM to examine sex differences in different brain structures. Further there are strong variations in study populations. The
study from Garcia-Falgueras et al. involved women and men between 18 and 33 years of age. As they pointed out there is a significant influence of sex hormones on certain brain structures. The results are therefore difficult to compare with previous MRI studies. Furthermore there was a correlation between olfactory function and the volume of the HC. This correlation was not as strong as reported earlier for other structures of the olfactory system, like the OB (Buschhüter et al., 2008). This relation between function and structure appears to be grounded mainly in adult neurogenesis and synaptogenesis. Adult neurogenesis accounts to a high degree for the plasticity especially of the olfactory system. Adult neurogenesis is mainly restricted to two regions, the subventricular zone (SVZ) and the subgranular layer of the dentate gyrus of the HC (Duan et al., 2008). The plasticity of the OB appears to be related largely to continuous neuronal supply from the SVZ. Here, neuroblasts migrate along the rostral migratory stream and replace interneurons (e.g., periglomerular cells, granular cells) in the OB leaving the major relay neurons, mitral cells, substantially unaffected (Curtis et al., 2007). Another mechanism concerns continuous synaptogenesis that occurs mainly between incoming axonal projections of olfactory receptor neurons and dendrites of mitral/tufted cells at the glomerular level. Both mechanisms are strongly related to input from olfactory receptor neurons (Lledo and Gheusi, 2003; Lledo et al., 2004). Neurogenesis in the HC begins with the production of new progenitor cells in the subgranular zone, followed by a relatively short migration to the inner granule cell layer, compared to the long way from the SVZ to the OB. Here, further differentiation into excitatory dentate granule cells takes place. As the HC is part of many neuronal networks with different functions it receives axonal inputs from different regions of the brain (Acsady and Kali, 2007). This leads to the assumption that hippocampal neurogenesis is influenced by more factors than the neurogenesis in the SVZ. These factors include the surrounding environment and ongoing cortical activity. A modulation of hippocampal neurogenesis has been shown for enriched environment, voluntary exercises, cognitive and emotional processes (Kempermann et al., 1997; Ma et al., 2009; van Praag et al., 1999). The stronger correlation between olfactory function and OB volume (Abolmaali et al., 2002; Buschhüter et al., 2008) than between olfactory function and the volume of structures like HC and AG, is likely explained by the fact that the OB seems to be exclusively involved in olfactory function. The present data obtained in a relatively large group of subjects can be used as age-related normative values of HC and AG volumes, separately for men, women and different age groups. These normative data will be helpful in the routine assessment of HC and AG volumes. This is of potential interest in diseases with acute or chronic impairment of olfactory function, in metabolic or neurodegenerative diseases or in disorders with damage of areas involved in adult neurogenesis. This can include iatrogenic causes like side effects of drugs, chemotherapy, radiotherapy or disease like stroke, infantile brain damage, or epileptic seizures. Acknowledgments Supported by the DDELTAS (Dijon-Dresden European Laboratories for Taste and Smell — LEA 549), underwritten by the Centre National de la Recherche Scientifique-Paris and the Technische Universität Dresden, and awarded to BS and TH. References Abolmaali, N.D., Hietschold, V., Vogl, T.J., Huettenbrink, K.B., Hummel, T., 2002. MR evaluation in patients with isolated anosmia since birth or early childhood. Am. J. Neuroradiol. 23, 157–164. Acsady, L., Kali, S., 2007. Models, structure, function: the transformation of cortical signals in the dentate gyrus. Prog. Brain Res. 163, 577–599.
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Amygdala volume marks the acute state in the early course of depression. Biol. Psychiatry 65, 812–818. van Praag, H., Kempermann, G., Gage, F.H., 1999. Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus. Nat. Neurosci. 2, 266–270. Velakoulis, D., Wood, S.J., Wong, M.T., McGorry, P.D., Yung, A., Phillips, L., Smith, D., Brewer, W., Proffitt, T., Desmond, P., Pantelis, C., 2006. Hippocampal and amygdala volumes according to psychosis stage and diagnosis: a magnetic resonance imaging study of chronic schizophrenia, first-episode psychosis, and ultra-high-risk individuals. Arch. Gen. Psychiatry 63, 139–149. Watson, C., Andermann, F., Gloor, P., Jones-Gotman, M., Peters, T., Evans, A., Olivier, A., Melanson, D., Leroux, G., 1992. Anatomic basis of amygdaloid and hippocampal volume measurement by magnetic resonance imaging. Neurology 42, 1743–1750. Wolfensberger, M., Schnieper, I., Welge-Lussen, A., 2000. “Sniffin' Sticks”: a new olfactory test battery. 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Is there a correlation between hippocampus and amygdala volume and olfactory function in healthy subjects? M. Smitka a, S. Puschmann b, D. Buschhueter b, J.C. Gerber c, M. Witt e, N. Honeycutt f, N. Abolmaali d, T. Hummel b,⁎ a
Department of Pediatrics, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany Department of Otorhinolaryngology, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany Department of Neuroradiology, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany d OncoRray & Institute and Policlinic for Diagnostic Radiology, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany e Department of Anatomy, University of Rostock, Gertrudenstr. 9, 18 057 Rostock, Germany f Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, 600 N. Wolfe St., Phipps 311, Baltimore, MD 21287, USA b c
a r t i c l e
i n f o
Article history: Received 15 April 2011 Revised 11 August 2011 Accepted 13 September 2011 Available online 24 September 2011 Keywords: Smell Nose Olfaction Brain Volumetry
a b s t r a c t Both amygdala (AG) and hippocampus (HC) are integral parts of the olfactory system. The present study, including a large number of healthy subjects, was performed to compare HC and AG volumes, measured by manual tracing, in relation to specific olfactory functions, including odor threshold, discrimination, identification, and odor memory tasks. It also aimed to provide age-related normative data about the volume of the HC and AG. A total of 117 healthy volunteers participated (age range 19–77 years, mean age 37 years; 62 women, 55 men). Using the “Sniffin' Sticks”, subjects received lateralized tests for odor threshold, and odor discrimination. In addition, an odor memory and an odor identification task were performed bilaterally. A Mini-MentalState test excluded dementia. MR scans were performed using a 1.5 T scanner for later manual volumetric measurements. Volumetric measurements exhibited a good reproducibility. The average volume for the right HC was 3.29 cm 3 (SD 0.47), for the left HC it was 3.15 cm 3 (SD 0.47). The average right AG had a volume of 1.60 cm 3 (SD 0.31), left 1.59 cm 3 (SD 0.3). Increasing age was accompanied by a decrease of HC and AG volumes, which were much more pronounced for the right compared to the left side. Only the volume of the right HC showed a small but significant correlation with odor threshold (r117 = 0.21; p = 0.02). Importantly, this correlation was not mediated by age as indicated by the significant partial correlation when controlling for age (r114 = 0.18; p = 0.049). In conclusion, the present data obtained in a relatively large group of subjects demonstrates a small correlation between the volume of the HC, as an integral part of the olfactory system, and smell function. In addition, these data can be used as the basis for normative values of HC and AG volumes, separately for men, women and different age groups. This is of potential interest in diseases with acute or chronic impairment of olfactory function, in metabolic or neurodegenerative diseases or in disorders with damage of areas involved in adult neurogenesis. © 2011 Elsevier Inc. All rights reserved.
Introduction In the adult mammal brain production of new neurons is almost limited to two particular regions, the hippocampus (HC) and the subventricular zone (Amrein and Lipp, 2009; Eriksson et al., 1998; Lee and Son, 2009). Concerning the latter, neurons derive from the walls of the lateral ventricles and migrate to the olfactory bulb (OB) (for a schematic representation of the olfactory system see Fig. 1). This has
⁎ Corresponding author. Fax: + 49 351 458 4326. E-mail address: [email protected] (T. Hummel). 1053-8119/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2011.09.024
been shown in animals and in humans (Curtis et al., 2007). The OB, which is the first relay station in the olfactory pathway, remains highly plastic throughout adult life. This has been shown by animal studies with olfactory deprivation. These animals had a reduction in OB volume due to the decreased number of cells (Cummings et al., 1997; Korol and Brunjes, 1992). In humans a significant correlation between OB volumes in relation to olfactory function was observed. This was shown to be independent of the subjects' age, although OB volumes decreased with age (Buschhüter et al., 2008; Yousem et al., 1997). Other neurons proliferate in the subgranular layer and differentiate into dentate gyrus cells of the HC. The hippocampal formation plays a prominent role in learning and memory, in spatial navigation
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definition of the anterior pole boundaries of 1.63 cm 3. The volume was measured using planimetry based on Nissl-stained serial sections (Brabec et al., 2010). The present study, including a large number of healthy subjects, was performed to compare HC and AG volumes, measured by manual tracing, in relation to specific olfactory functions. It also aimed to provide age-related normative data about the volumes of the HC and AG. These normative data for different decades of life would be necessary to realize the idea of volumetry of the HC and the AG as a tool which may help to assess stage and course of diseases associated with olfactory loss. Materials and methods Volunteers and study design
Fig. 1. Schematic diagram of the major olfactory pathways. Regions in gray together represent the primary olfactory cortex. Projections between the olfactory bulb and most areas of the primary olfactory cortex are bidirectional, with the exception of the anterior perforated substance (OTu). Similarly, associational connections between the primary olfactory cortex subregions are reciprocal, apart from OTu. The downstream targets of the primary olfactory cortex represent some of the major projection sites (bottom of figure), many of which provide feedback to the primary olfactory cortex (not shown), but these connections are not meant to be comprehensive or all-inclusive. While broadly illustrative of the human olfactory system, this diagram is largely based on information obtained from animal models, due to the scarcity of human data. ACo = anterior cortical nucleus of the amygdala; aINS = agranular insula; BLA = basolateral nucleus of the amygdala; EC = entorhinal cortex; HPC = hippocampus; HYP = hypothalamus; MD = mediodorsal thalamus; PAC = periamygdaloid cortex; PIR = piriform cortex; PR = perirhinal cortex; VP = ventral pallidum; VS = ventral striatum. Figure and legend from Gottfried, J. in Hummel T, Welge-Lüssen A (eds): Taste and Smell. An Update. Adv Otorhinolaryngol 2006, vol 63, pp 44–69; with kind permission from S. KArger AG, Basel, Switzerland.
and control of attention (Sahay and Hen, 2007). It is not an integral part of the primary olfactory cortex, but it receives strong afferent input from the entorhinal cortex. In contrast, the neighboring amygdalae (AG) are part of the primary olfactory cortex (Gottfried et al., 2002). The size and structural plasticity of HC and AG have been previously studied in patients with Alzheimer dementia (Barnes et al., 2009; Horínek et al., 2007; Teipel et al., 2008), in temporal lobe epilepsy (Akhondi-Asl et al., 2011; Mechanic-Hamilton et al., 2009; Pardoe et al., 2009; Scorzin et al., 2008), in multiple sclerosis (Anderson et al., 2010), in schizophrenia (Klaer et al., 2010; Teipel et al., 2010), in aphasia after middle cerebral artery stroke (Meinzer et al., 2010), in autism spectrum disorder (Zeegers et al., 2009), in depression (Tae et al., 2008; van Eijndhoven et al., 2009), in acute psychosis (Velakoulis et al., 2006), in patients with bipolar disorder (Doty et al., 2008), and also in subjects with olfactory loss (Yousem et al., 1996a, 1996b). However, these studies included either only a small control group or no controls at all. Most studies use automated volumetric measurements (e.g. FreeSurfer, Individual Brain Atlases using Statistical Parametric Mapping) or auto-assisted manual tracings. The results in these studies displayed significant variations in terms of volume. For example AG volumes were published ranging from 1.15 cm 3 on the left side and 1.16 cm 3 on the right side (Pruessner et al., 2000) to 3.34 cm 3 on the left side and 3.44 cm 3 on the right side (Watson et al., 1992). Studies showing smaller volumes of the AG (between 1 and 2 cm 3) are supported by an anatomical study which showed an average size of the classic AG of 1.24 cm 3 and in the AG with another
A total of 117 randomly selected, subjectively normosmic individuals (55 men and 62 women), aged 19 to 79 years (mean ± standard deviation = 37 ± 17 years), participated in this study. The investigations were performed in accordance to the Declaration of Helsinki on Biomedical Studies Involving Human Subjects (World Medical Association, 1997). The study design was approved by the University of Dresden Medical Faculty Ethics Review Board (number EK 239112006). All subjects provided written informed consent for the study aims and procedures and attended our Smell and Taste Clinic for detailed diagnostic evaluation. All participants received an otorhinolaryngological investigation including a volumetric MRI scan of the entire brain, and detailed lateralized olfactory tests. In addition, subjects received an extensive review of their clinical histories in order to exclude a possible cause of smell dysfunction. In particular medical history included otorhinolaryngological, neurological and psychiatric disorders. Chronic rhinosinusitis was excluded by medical history and MR-images. Furthermore, all subjects underwent a mini mental state examination (MMSE) to screen systematically for possible cognitive impairment. Subjects were recruited by flyers at the associated university and “mouth to mouth propaganda”. Handedness was not used as a selection criteria, as normative values should be obtained in the general population. Olfactory testing Psychophysical testing of olfactory function was performed with the validated “Sniffin' Sticks” test (Hummel et al., 1997; Kobal et al., 2000). Olfactory testing comprised three tests, namely tests for odor threshold, odor discrimination and odor identification. To prevent visual cues during the assessment of odor thresholds and odor discrimination, subjects were blindfolded with a sleeping mask. Results from olfactory testing can be analyzed separately from each other. Overall olfactory function is expressed as the sum of the scores from the 3 individual tests (Wolfensberger et al., 2000). Magnetic resonance imaging All examinations were performed at a 1.5-Tesla magnetic resonance imaging system (Magnetom Sonata; Siemens, Erlangen, Germany) using the 8-channel cp-head coil. Volumes of the right and left HC and AG were determined using the MRI scans of the brain and a standardized protocol for HC and AG analysis. The protocol included: 1) 5mm-thick standard T2-weighted fast spin-echo images covering the whole brain without interslice gap to rule out any organic brain disorders; and 2) 1-mm-thick T1-weighted fast spin-echo images without interslice gap in the sagittal plane. Nine MRI datasets were of good quality, sufficient for data analysis; 108 MRI datasets were of excellent quality. MRI-sequences of minor quality were repeated immediately during assessment. To additionally investigate the reliability, volumetric measurements of the right and left HC and AG were performed by two
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independent observers, blinded to the olfactory test results, by manual segmentation using the AMIRA 3D visualization and modeling system (Visage Imaging, Carlsbad, USA). The segmentation protocol applied the anatomical boundaries that were proposed by Pruessner et al., 2000, and adapted to the actual software and datasets. Analysis was performed on sagittal, coronal and horizontal images. After completion of the planimetric manual contouring all images were reviewed and refined before calculation of volumes was carried out. Manual contouring of the HC started on the sagittal plane, beginning laterally. Tube-shaped gray matter spreads out within the inferior horn of the lateral ventricle. The medial boundaries are defined by the ventricle. The choroid plexus needs to be excluded from the measurements (Malykhin et al., 2007). The inferior and dorsal borders are identified by transition of gray to white matter. The frontomedial demarcation to the AG is built by the alveus. The coronal planes are examined next, beginning anteriorly and moving posteriorly. The inferior borders are clearly perceptible by the mostly triangular form of white matter. The HC can be discriminated against the superior localized AG. The lateral, anterior and superior borders of the hippocampal head is identified by the uncal recess of the inferior horn of the lateral ventricle. Body and tail of the HC are limited medially by white matter and laterally by the ventricle. The HC is followed to the point where gray matter is seen inferomedially from the collateral
trigone of the lateral ventricle (Killiany et al., 2005). As next step the horizontal planes are examined. These are helpful in defining the anterior and medial borders. Anteriorly the HC exhibits an S-shaped form and is defined by the AG. The olive-shaped AG is located superior and anterior to the head of the HC (Fig. 2). Volumetric measurement of the AG starts in the sagittal planes. In the inferior horn of the lateral ventricle anterosuperiorly of the HC a bean-shaped mass of gray matter is followed medially, where it grows in size. This mass is only in parts clearly defined by white matter and cerebrospinal fluid. Anterosuperiorly a thin layer of white mater defines the border to the periamygdaloid cortex. The coronal planes are followed from posterior to anterior, starting where gray matter is first localized above the alveus (Pruessner et al., 2000). Medially the AG is defined by the HC, laterally by white matter and gray matter of the caudate nucleus, which is not included (Malykhin et al., 2007). Anteromedially the AG is separated from the entorhinal cortex by a thin layer of white matter (Convit et al., 1999). In the horizontal planes the medial border is defined by the by the ambient cistern postero-superiorly. Whole brain volumes were calculated after contouring on 5-mmthick coronal planes, beginning anteriorly. The assessment was based on T2-weighted fast spin-echo images covering the whole brain without interslice gap. Subarachnoid and ventricular CSF was excluded from intracranial volume. In a first step an automatic
Fig. 2. Example for measurement of HC in the inferior horn of the lateral ventricle (dark border) and the olive-shaped AG which is located antero-superiorly to the HC (bright border), using AMIRA 3D visualization software (Visage Imaging GmbH, Berlin, Germany). The borders were defined manually on each slide in every direction (sagittal, coronal, horizontal). AMIRA allows a 3-dimensional reconstruction of the examined structures by co-registration of the borders in all three planes.
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segmentation procedure, implemented in AMIRA software was used. In a second step borders were manually redefined. Statistical analysis All statistics were performed using SPSS software version 15.0 (SPSS Inc., Chicago, IL, USA). Correlations according to Pearson were computed between volumetric measurements of the HC and AG and functional measurements. In addition, partial correlations controlling for age were performed. The level of significance was set at 0.05.
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left-sided volumes of HC and AG exhibited only a tendency towards a significant correlation (HC: r117 = −0.17, p = 0.076; AG: r117 = −0.16, p = 0.085) while the correlation was much stronger for the right side (HC: r117 = − 0.28, p = 0.003; AG: r117 = − 0.23, p = 0.014). Correlation with olfactory function Only the right HC showed a small but significant correlation between olfactory function (threshold) and volume (r117 = 0.21; p = 0.02) (Fig. 3). This correlation was not mediated by age as indicated by the significant partial correlation when controlling for age (r114 = 0.18; p = 0.049). Such correlations were not seen in the AG.
Results Olfactory function Volumetric measures of HC and AG Interindividual variations in AG and HC volumes were relatively large, ranging from 2.09 cm 3 to 4.49 cm 3 for right HC volumes and from 1.8 cm 3 to 4.45 cm 3 for left HC volumes. The volumes for the right AG ranged from 0.21 cm 3 to 2.67 cm 3 and for the left AG from 0.97 to 2.75 cm 3. Mean volumes for the entire brain were 1270 cm 3 for women (SD 113.44) and 1445 cm 3 for men (SD 122.26). In contrast, intraindividual variation was relatively small (correlation between left-sided and right-sided HC volumes: r117 = 0.79, p b 0.001); correlation between left-sided and right-sided AG volumes: r117 = 0.78, p b 0.001). The maximum intraindividual difference between left-sided and right-sided HC volumes was 0.77 cm 3 for men and 0.73 cm 3 for women, between left-sided and right-sided AG volumes was 0.79 cm 3 for men and 0.45 cm 3 for women. Side differences Mean volume of the right HC was 3.29 cm 3 (SD 0.47), mean volume of the left HC was 3.15 cm 3 (SD 0.47; p b 0.001). Such differences were not seen in the AG (right AG: 1.60 cm 3; SD 0.31; left AG: 1.59 cm 3; SD 0.3; p = 0.42). Sex differences On average, HC and AG volumes of men (HC right: 3.34 cm 3; SD 0.47; HC left: 3.2 cm 3; SD 0.47; AG right: 1.66 cm 3; SD 0.34; AG left: 1.66 cm 3; SD 0.31) were found to be larger than those of women (HC right: 3.25 mm 3; SD 0.47; HC left: 3.1 cm 3; SD 0.46; AG right: 1.55 cm 3; SD 0.26; AG left: 1.52 cm 3; SD 0.27). However, this was only significant for AG (p = 0.016) but not for HC (0.24). Age differences Left and right HC and AG volumes were relatively stable up to the 4th decade of life and declined in the 6th and 7th decades. However,
Average TDI scores for olfactory function were 33.7 (SD 3.4; range 24.8–42.1). Side differences Odor discrimination tended to be better on the right compared to the left side (p = 0.082). However, no such differences were found for odor identification (p = 0.25). Sex differences Women significantly outperformed men in terms of odor thresholds (p = 0.036), but not in odor discrimination (p = 0.11), odor identification (p = 0.74), or odor memory (p = 0.97). Age differences Odor memory decreased significantly with advancing age (r117 =0.28, p=0.002). Furthermore, odor discrimination was found to decrease on left and right sides (left: r117 =−0.35, pb 0.001; right: r117 =−0.23, p=0.015) while odor threshold decreased only on the left side (left: r117 =−0.31, p=0.001; right: r117 =−0.13, p=0.16). Odor identification scores did not correlate with age (r117 =−0.10, p=0.27). Volumetric measures — normative values A normal HC or AG volume was defined to be above the 10th percentile of the distribution of volumes within the investigated population. Thus, the following normative data arose from the current dataset: for men b45 years (n = 31) the HC should have a minimum volume of 2.99 cm 3; and for men N45 years (n = 24) the HC should have a minimum volume of 2.57 cm 3. The volume of the AG for men b45 years should be greater than 1.52 cm 3 and for men N45 years the volume of the AG the minimum volume is 1.36 cm 3. For women b45 years of age (n = 35) the volume of the HC should
Fig. 3. Relationship between the volumes of HC (in ccm) and phenyl ethyl alcohol odor thresholds (in dilution steps). In general, higher sensitivity is related to larger volumes of the HC. However, this was only significant for right-sided measures (r117 = 0.21, p = 0.02).
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have a minimum volume of 2.76 cm 3, and for women N45 years (n = 27) the volume should be at least 2.66 cm 3. The volume of the AG for women b45 years should be greater than 1.34 cm 3, and for women N45 years the volume of the AG should exceed 1.18 cm 3. The mean total volume for women of the HC for men b45 years of age was 6.44 cm 3 (SD 0.94), the mean total volume of the AG was 3.16 cm 3 (SD 0.55). For women N45 years the mean total volume of the HC was 6.22 cm 3 (SD 0.83; reduction in size of 4%), the mean total volume of the AG was 2.96 cm 3 (SD 0.41; reduction in size of 6.4%). The mean total volume for men of the HC for men b45 years of age was 6.78 cm 3 (SD 0.75), the mean total volume of the AG was 3.43 cm 3 (SD 0.52). For men N45 years the mean total volume of the HC was 6.23 cm 3 (SD 0.95; reduction in size of 8.2%), the mean total volume of the AG was 3.19 cm 3 (SD 0.7; reduction in size of 7%). Overall this means a reduction in size of the HC and AG on average of approximately 6%. This is comparable with the reduction in size of the whole brain for the volunteers b45 years from 1394.4 cm 3 to 1296.8 cm 3 in volunteers N45 years (reduction in size of 7%). Discussion In agreement with previous research the data in the present study confirmed the range of HC and AG volumes measured by volumetric MRI-analysis from other groups and by anatomical studies (Brabec et al., 2010; Pruessner et al., 2000). The volume of the HC was in excellent accordance with other authors (Pruessner et al., 2000). Local adaptations of the proposed protocol had no major influence on the overall results. This is strong support for applying the protocol as guideline for measurements of the HC. In contrast to the HC there is a discrepancy for AG volumes compared with the study by Pruessner et al. Results can be influenced by differences in the MRI-scanner, different acquisition techniques, sample size and population or adaptations of the segmentation-protocol. Above that the definition of the AG as stated by Brabec et al has a significant influence on the volumes. As the average volume in a study using planimetry of Nisslstained serial sections for the classic AG was 1.24 cm3, the average volume for the AG with wider borders was 1.63 cm3. This included the area of more diffusely scattered cells under the anterior pole of the amygdale, the area praeamygdalaris, and the sublenticular part of the extended amygdale as it continues to the substantia innominata under the globus pallidus (Brabec et al., 2010). As interindividual variations in AG and HC volumes were relatively large, small sample size numbers can have a strong influence on the overall results. This study enhances the aforementioned studies by applying manual segmentation on a relatively large number of 117 1.5T-MRI datasets by two blinded observers, therefore enhancing statistical power. The observed side differences for HC volumes with larger volumes in the right hemisphere are in accordance with most studies on HC volumetry (Pruessner et al., 2000). As the HC is an integral part of different functional circuits and has a wide range of functions a definitive cause for this observation remains unknown. There is accumulating evidence on the basis of psychophysical, clinical, electrophysiological, and imaging studies that, in general, the right hemisphere is more important to the sense of smell than the left hemisphere (Fulbright et al., 1998; Hummel et al., 1995; Sobel et al., 1999; Yousem et al., 1999; Zatorre et al., 1992). This might contribute to the frequently reported side differences of the HC. There was a significant correlation between the size of the HC and AG and the age of the volunteers, independent of sex. In contrast to the present study other groups studying the expression of sex differences in the human olfactory system found significant gender differences of AG and HC (Garcia-Falgueras et al., 2006). Garcia-Falgueras et al. used VBM to examine sex differences in different brain structures. Further there are strong variations in study populations. The
study from Garcia-Falgueras et al. involved women and men between 18 and 33 years of age. As they pointed out there is a significant influence of sex hormones on certain brain structures. The results are therefore difficult to compare with previous MRI studies. Furthermore there was a correlation between olfactory function and the volume of the HC. This correlation was not as strong as reported earlier for other structures of the olfactory system, like the OB (Buschhüter et al., 2008). This relation between function and structure appears to be grounded mainly in adult neurogenesis and synaptogenesis. Adult neurogenesis accounts to a high degree for the plasticity especially of the olfactory system. Adult neurogenesis is mainly restricted to two regions, the subventricular zone (SVZ) and the subgranular layer of the dentate gyrus of the HC (Duan et al., 2008). The plasticity of the OB appears to be related largely to continuous neuronal supply from the SVZ. Here, neuroblasts migrate along the rostral migratory stream and replace interneurons (e.g., periglomerular cells, granular cells) in the OB leaving the major relay neurons, mitral cells, substantially unaffected (Curtis et al., 2007). Another mechanism concerns continuous synaptogenesis that occurs mainly between incoming axonal projections of olfactory receptor neurons and dendrites of mitral/tufted cells at the glomerular level. Both mechanisms are strongly related to input from olfactory receptor neurons (Lledo and Gheusi, 2003; Lledo et al., 2004). Neurogenesis in the HC begins with the production of new progenitor cells in the subgranular zone, followed by a relatively short migration to the inner granule cell layer, compared to the long way from the SVZ to the OB. Here, further differentiation into excitatory dentate granule cells takes place. As the HC is part of many neuronal networks with different functions it receives axonal inputs from different regions of the brain (Acsady and Kali, 2007). This leads to the assumption that hippocampal neurogenesis is influenced by more factors than the neurogenesis in the SVZ. These factors include the surrounding environment and ongoing cortical activity. A modulation of hippocampal neurogenesis has been shown for enriched environment, voluntary exercises, cognitive and emotional processes (Kempermann et al., 1997; Ma et al., 2009; van Praag et al., 1999). The stronger correlation between olfactory function and OB volume (Abolmaali et al., 2002; Buschhüter et al., 2008) than between olfactory function and the volume of structures like HC and AG, is likely explained by the fact that the OB seems to be exclusively involved in olfactory function. The present data obtained in a relatively large group of subjects can be used as age-related normative values of HC and AG volumes, separately for men, women and different age groups. These normative data will be helpful in the routine assessment of HC and AG volumes. This is of potential interest in diseases with acute or chronic impairment of olfactory function, in metabolic or neurodegenerative diseases or in disorders with damage of areas involved in adult neurogenesis. This can include iatrogenic causes like side effects of drugs, chemotherapy, radiotherapy or disease like stroke, infantile brain damage, or epileptic seizures. Acknowledgments Supported by the DDELTAS (Dijon-Dresden European Laboratories for Taste and Smell — LEA 549), underwritten by the Centre National de la Recherche Scientifique-Paris and the Technische Universität Dresden, and awarded to BS and TH. References Abolmaali, N.D., Hietschold, V., Vogl, T.J., Huettenbrink, K.B., Hummel, T., 2002. MR evaluation in patients with isolated anosmia since birth or early childhood. Am. J. Neuroradiol. 23, 157–164. Acsady, L., Kali, S., 2007. Models, structure, function: the transformation of cortical signals in the dentate gyrus. Prog. Brain Res. 163, 577–599.
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