Synergistic effects of edible plants with light environment on the emotion and sleep of humans in long-duration isolated environment

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Synergistic effects of edible plants with light environment on the emotion and sleep of humans in long-duration isolated environment Wenzhu Zhang , Hui Liu , Zhaoming Li , Hong Liu PII: DOI: Reference:

S2214-5524(19)30140-3 https://doi.org/10.1016/j.lssr.2019.11.003 LSSR 258

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Life Sciences in Space Research

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25 June 2019 22 August 2019 18 November 2019

Please cite this article as: Wenzhu Zhang , Hui Liu , Zhaoming Li , Hong Liu , Synergistic effects of edible plants with light environment on the emotion and sleep of humans in long-duration isolated environment, Life Sciences in Space Research (2019), doi: https://doi.org/10.1016/j.lssr.2019.11.003

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Synergistic effects of edible plants with light environment on the emotion and sleep of humans in long-duration isolated environment Wenzhu Zhanga,c, Hui Liua,b,c,d,*, Zhaoming Lia,c, Hong Liua,b,c,* * a

Institute of Environmental Biology and Life Support Technology, School of

Biological Science and Medical Engineering, Beihang University, Beijing 100083, China b

Beijing Advanced Innovation Center for Biomedical Engineering, Beihang

University, Beijing, 100083, China c

International Joint Research Center of Aerospace Biotechnology & Medical

Engineering, Beihang University, Beijing 100191, China d

School of Aviation Science and Engineering, Beihang University, Beijing

100083, China * Corresponding author. E-mail: [email protected] ** Corresponding author. E-mail: [email protected] TEL: (86)-10-82339837 FAX: (86)-10-82339283

Highlights 1.

Edible plants and light environment improved not only emotional state but also sleep quality in the long-duration isolated environment.

2.

Strawberry had a better effect than purple rape and coriander on 1

improving positive emotion. 3.

Exposure to coriander could reduce sleep latency and REM latency.

4.

There was a positive synergistic effect of edible plant with different light environment on micro-awakening index and sleep efficiency.

Abstract The emotion and sleep-related problems of humans who are on mission of deep-space and deep-sea exploration are topics of special interest because of the isolated environment. Effective regulatory approaches should be developed to manage the positive emotions and sleep quality in a long-duration isolated environment. The results reported that emotion and sleep were closely linked to each other because plants could significantly regulate humans’ emotion and sleep through their own color and fragrance. Additionally, the light conditions prevailing in that location also had significant influence on humans’ emotion and sleep. There have been few reports on the synergistic effects of plants with light environment on humans’ physical and mental health. In this research, three species of edible plants and three color temperature levels that were commonly used in people’s living environment were selected. Then orthogonal tests were conducted in the cabins of “Lunar Palace I” in the middle of the third phase of the “Lunar Palace 365” experiment, and salivary cortisol levels, emotion, and sleep conditions of the volunteers were measured. The results showed that in the long-duration isolated 2

environment, strawberry had a better effect than purple rape and coriander on improving positive emotion. Exposure to coriander before bedtime might help people to rapidly go to sleep, increase sleep integrity, and sleep efficiency in the isolated environment. Moreover, there appeared to be a positive synergistic effect of edible plants with light environment on micro-awakening index and sleep efficiency. These results provided a scientific basis for improving the physiological and psychological health of people in the long-duration isolated environment by changing the light environment with appropriate plants. Keywords: isolated environment; emotion; sleep; edible plants; light environment

1. Introduction Psychological difficult-to-mitigate

health risks

risk of

is

one

confinement

of

the

during

most manned

serious

and

deep-space

exploration and deep-sea exploration (Basner et al., 2014). In a space capsule or station, the environment is isolated, and communication with the outside world is limited to telephone or delayed video (Zikai et al., 2019). Crew members have to live and work in an isolated environment for a long time when they perform deep-space and deep-sea exploration missions (Alfano et al., 2018). In addition, some special people have to stay on board for a long time because of various inconveniences. Long-term disconnection from the 3

natural environment can lead to some mental problems such as emotional deterioration (Oh et al., 2019). Emotions and sleep problems are often closely related to each other (Gerhardsson at al., 2018; Zheng et al., 2018). Therefore, it is particularly important to find a way to improve humans’ positive emotions and sleep quality without side effects in an isolated, confined environment such as space station, submarine, and extraterritorial base. Natural environment plays an important role in health promotion. Humans have an innate desire to interact with the natural environment (Kaplan, 1995; Ulrich et al., 1991). The emotional, cognitive, physical, and social functions of humans can be improved by exposure to plants and by plant-related activities (Bratman et al., 2015). With regard to this aspect, traditional views are that the environment we live is composed of plants, and we often show positive psychological and physiological responses to plants (King, 2015). Furthermore, an increasing number of studies have confirmed that active or passive interaction with plants could be beneficial to physical and mental health (Matsumoto et al., 2014; Sin-Ae et al., 2017; Soga et al., 2017). The color and volatile compounds of plants may play major roles in this process. Human body's perception of color is mainly achieved by light, and plants of different colors reflect light with different wavelengths. Light is sensed by intrinsically photosensitive retinal ganglion cells (ipRGCs) and projected to the paraventricular nucleus of the hypothalamus, which regulates cortisol secretion by stimulating the adrenal gland (Bedrosian et al., 2013). Thus, 4

cortisol level could reflect stressful and emotional conditions of people (Duesenberg et al., 2016). Studies have shown that the green color of plants could effectively restore the brainwave and mental state of workers, reduce pain in the shoulders and back, and relieve work stress. In addition, it also makes people feel calm, reduces pulse and blood pressure, regulates the inner balance of the body, and helps overcome insomnia (Bringslimark et al., 2009). Volatile compounds of plants are beneficial to people’s mental and emotional health, such as relieving anxiety and depression and maintaining the memory of individuals with Alzheimer’s disease or other memory impairments (Cohen-Mansfield et al., 1999). The volatile compounds extracted from lavender improve sleep (Lillehei et al., 2015). The limbic system is closely connected to the olfactory system; hence, it is associated with emotion and sleep regulation (Brennan et al., 1990; Herz et al., 2004a). Moreover, stress and self-esteem could be regulated by horticultural activities (Jo et al., 2013). However, traditional horticultural treatments are mostly carried out in outdoor forests and parks. The use of trees and shrubs in horticultural therapy could not be applied to indoors and special isolated environments. In outdoor cultivation, plants have the characteristics of bright colors and fragrance and release negative oxygen ions; vegetables are also edible, easily cultivable, and dwarf. Furthermore, vegetable tasting could promote the well-being of people in isolated environments. The technology for indoor vegetable cultivation has gradually matured with the development of plant factory, which 5

provides technical support for the application of dwarf vegetables in indoor horticultural therapy. However, there have been few reports on the application of dwarf vegetables in horticultural therapy. Additionally, light has a regulatory effect on human emotions and sleep; information is sensed by the ipRGCs and passed on to the suprachiasmatic nucleus (SCN) (Dijk et al., 2009; Han and Lee, 2017). The SCN projects the information not only to areas involving mood regulation but also to the hypothalamic paraventricular nucleus to regulate melatonin secretion by the pineal gland. Different light environments have different influences on emotion and sleep. Several studies have investigated the influence of light environment on human physiology through biochemical markers such as cortisol (Sroykham et al., 2015), and biosignals such as electrocardiography (ECG) (Sroykham et al., 2015) or electroencephalography (EEG) (Minguillon et al., 2017) signals. Vigor had a higher score for yellow light than for other lights in a treatment room (Han and Lee, 2017). Female employees who had worked in an office for a long time showed that warm light could increase their positive emotion (Lskra et al., 2012). In addition, different colors of light could affect the EEG, and blue light increased the intensity of the beta wave and reduced sleep efficiency (Rahman et al., 2014). To date, although there is plenty of preliminary evidence that plants and light environment regulate the physiological and psychological conditions of humans, there are few reports on the synergistic effects of plants with light 6

environment on the emotion and sleep of humans. The light environment in which we live and work is generally white light. Therefore, it is of great practical significance to adjust the color temperature of white light to make it “warm” or “cold” to adapt to our work and life. The aim of the present study is to investigate the synergistic effects of edible plants with light environment on humans’ psychological and physiological responses in a long-duration isolated environment.

2. Method This research was supported by “Lunar Palace 365”, which was a 370-day, multi-crew, closed experiment carried out in a platform with ground-based experimental bioregenerative life support system (BLSS), named Lunar Palace 1 (Hao et al., 2019). The “Lunar Palace 365” provided good opportunity to perform psycho-physiological research in such long-duration isolated environment. The tests were conducted in the bedrooms (3 m2) that had stainless wall, ceiling, bed, and desk at the middle stage of the third phase of the “Lunar Palace 365” experiment (2018.3.22–2018.4.22; Figure 1). The temperature and relative humidity were maintained at 25±2 oC and 55±5%, respectively, throughout the experiment. When the test began, volunteers have already lived in the isolated environment for 56 days. 2.1 Participants 7

The participants were four students (two males and two females) of Beihang University aged 28 ± 2 years, who were nonsmokers, and who had no history of physical or psychological disorders. Alcohol, tobacco, and caffeine intake was prohibited throughout the experimental period. Before the start of the experiment, the test process was fully explained excluding the purpose of the study, and participants’ informed consent was obtained. This study was approved by the Science and Ethics Committee of School of Biological Science and Medical Engineering, Beihang University, Beijing, China (Approval ID: BM20180003). 2.2 Protocol This experiment was designed as an orthogonal experiment with two factors at three levels. The edible plants were purple canola, coriander, and strawberry. The color temperature levels of the light environment were 3000 K, 4500 K, and 6000 K (Figure 2a). Figure 2b shows the overall experimental protocol, which took 8.5 hours. The experiment was conducted in five stages: in the first stage, after explaining the test details and protocol to each participant, physiological measurement devices such as polysomnography (PSG) device were prepared. The volunteers were then asked to relax fully during a rest period of 1 to 2 min with eyes closed. Subsequently, the volunteers answered the Profile of Mood States (POMS) and Positive and Negative Affect Schedule (PANAS) questionnaires. The first saliva sample was collected under the regular indoor light environment (6000 K) without 8

plants. Then the volunteers were asked to watch and touch edible plants under designated light environments, and the quantity of each kind of plant was kept consistent (plant cultivation area of the container: 40 cm * 30 cm, 35-day-old plants, with the plant crown covering the entire cultivation container). The second saliva sample was collected at the end of the third stage. Thereafter, the volunteers were required to turn off the light, go to bed, and turn on the PSG device to perform real-time monitoring of EEG for 8 hours. Lastly, the participants answered the POMS and PANAS questionnaires, and the PSG device was turned off after they woke up the next morning. 2.3 Subjective evaluation We used the POMS and PANAS questionnaires to evaluate the effects of different combinations of edible plants and light environments on subjective emotions. POMS is a psychological rating scale for assessing short-term and unique emotional states (Zhu, 1995). A brief version comprising 40 items was used to reduce the time required for the measure. The items were rated on a 4-point scale ranging from “not at all” to “extremely” and included seven types of mood states: tension–anxiety (T-A), anger–hostility (A-H), fatigue (F), dejection (D), confusion (C), vigor (V), and self-esteem (S-E). The total mood disturbance (TMD) score was calculated using the following formula:

TMD =  T  A  +  A  H  +  F +  D  +  C    V   S  E  . 9

PANAS was used to detect fluctuations in mood for a short period (Qiu et al., 2008). Volunteers rated the extent to which they currently experienced each feeling on a 5-point scale (1=Very slightly or not at all, 2=A little, 3=Moderately, 4=Quite a bit, 5=Extremely). The PANAS questionnaire consists of 10 positive (e.g., enthusiastic, active, and proud) and 10 negative (e.g., irritable, frightened, and ashamed) mood words. 2.4 Measurement of Cortisol Volunteers' saliva samples were collected at phases 2, 3, and 5. Saliva was collected with saliva collection tubes (Sarstedt Salivettes®), which are plastic tubes containing a cotton wool swab that volunteers had to chew for 3 minutes. Cortisol concentrations were detected using a human cortisol ELISA kit (Rigorbio Ltd., Beijing, China). 2.5 Measurement of sleep quality PSG recording was performed using a portable sleep recorder (Philips, PDx) in the isolated cabins. Standard electrode montage was used (C3 and C4) referenced versus contralateral mastoids in addition to two submental electrodes and electrodes at the outer canthi of the eyes. The PSG device was turned on at the beginning of the fourth stage and turned off at the end of the stage, performed according to American Academy of Sleep Medicine (AASM) standards. Moreover, we also used PSG to detect the electrocardiograms. The W, N1, N2, N3, and R periods of sleep and the micro-awakening events were manually interpreted according to electroencephalogram (EEG), 10

electrooculogram (EOG), and electromyogram (EMG) signals. Finally, sleep latency, Rapid eye Movement (REM) latency, micro-awakening index, and sleep efficiency were calculated using Alice® SleepwareTM 2.8.39 software and by manual correction. 2.6 Data analysis All analyses were carried out using SPSS (version 25). As our sample size was very small and did not meet the assumptions for parametric analysis, we analyzed the data using Friedman test. The Friedman test is a nonparametric statistical method developed to detect differences in treatments across multiple test attempts (Conover et al., 1980). We then used Wilcoxon’s signed-rank test to identify significant differences between the three edible plants. The data of cortisol levels and subjective emotional evaluation were calculated as the amount of change before and after the treatment. Spearman's correlation coefficient and regression analysis were performed to evaluate the connection between emotion and sleep. Statistical validity was established at P < 0.05. 3 Result 3.1 Objective emotion Cortisol was used to indicate the physiological changes caused by edible plants and light environment. Figure 3 shows variation in cortisol concentrations after 15 minutes of watching and touching plants in different light environments. Cortisol concentration reduced in the strawberry and 11

coriander groups in a light environment with 4500 K or 3000 K color temperature when compared with those in other light treatments, but the cortisol concentration in the purple rape group did not show any obvious reducing trend. This indicates that strawberry and coriander could reduce negative emotion. Moreover, the cortisol concentration in the strawberry group reduced along with a decrease in the color temperature, indicating that there might be a synergistic effect between edible plants and light environment. 3.2 Subjective emotion The results of the PANAS and POMS questionnaires showed similar trends of the effects of different combinations of edible plants and light environments on the subjective emotions of the participants. More positive psychological relaxation was seen for the stimulus involving strawberry than for those of purple rape and coriander (Figures 4 and 5). Among the subcategories, F was lower as well as V and S-E were higher when performing the task with strawberry than with other plants (Figure 5a, b, c); S-E showed statistical difference in light environments with the color temperature of 6000 K (X2 =7.429, P=0.024). TMD scores of the strawberry group were lower than those of the other groups, and there was a statistically significant difference for the 6000 K light environment (X2 =8.977, P=0.011) (Figure 5d). 3.3 Sleep quality EEG results showed that sleep latency in the coriander group was shorter than that in the purple rape and strawberry groups (2–30 min), and there was a 12

statistically significant difference for the 4500 K light environment (X2 =6.533, P=0.038; Figure 6a). In addition, the sleep latency of each edible plant in the 3000 K light environment was shorter than that in the other groups (0–17.8 min), which suggested that the light environments play a role in the sleep intervention in addition to the edible plants. These results show that exposure to coriander and the 3000 K light environment before going to bed might help people to go to sleep quickly in the isolated environment. REM latency in the coriander group was also shorter than that in the purple rape and strawberry groups (10.3–45.5 min), and the differences were statistically significant for the 4500 K light environment (X2 =6.000, P=0.05; Figure 6b). These results showed that coriander could shorten the time to reach deep sleep. Micro-awakening index can indicate the integrity of sleep. The micro-awakening index of coriander was lower than that of purple rape and strawberry in the 3000 K color temperature (1.3–1.7). Sleep efficiency was higher in coriander than in the other two edible plants (0.7–2.1%). Moreover, we found that edible plants reduced micro-awakening index and increased sleep efficiency with decrease in the color temperature of the light environment (Figure 6c, 6d), suggesting that there might be synergistic effects of edible plants and light environments. 4 Discussion

13

Volunteers of this study had lived in this isolation environment for 56 days when the experiment began. The status of their emotion and sleep had already remained in the stable phase (Hao et al., 2019). The “Lunar Palace 365” project, which simulated survival in extraterritorial base such as Lunar base and Mars base, provided an outstanding opportunity to research the changes and interventions in psycho-physiological states in long-term isolation. Hence, the results obtained in this study has an important reference value. To acquire the data of participants’ emotion under different stimuli comprehensively, cortisol concentration was chosen to indicate the emotional changes from the aspect of physiology, and subjective questionnaires (POMS and PANAS) were used to evaluate the change in subjective emotion. First, cortisol was chosen because it is a purported biomarker of the hypothalamic–pituitary–adrenal (HPA) axis can be activated by negative emotion. Moreover, it is a primary biomarker for psychological stress and a reliable indicator of emotional well-being. In this study, the average cortisol concentration showed a decreasing trend in the strawberry and coriander groups in light environments with 4500 K and 3000 K color temperature (Figure 3), with no statistically significant difference. This might be due to the small sample size. Hence, we analyzed the changes in cortisol levels of the four participants in response to nine stimuli separately. The results showed that the cortisol concentrations of more than half of the volunteers (volunteers A, C, and D) were decreased in the strawberry and coriander groups with 4500 14

K and 3000 K light environments, although inter-individual differences were observed (Figure A1). Van et al. reported that after giving a pressure to volunteers to increase cortisol concentrations, then emotion and cortisol levels of volunteers could be recovered after 30 min gardening activities (Van and Custers, 2011). These results indicated that strawberry and coriander could improve human emotion under “warm” light. Comparing the three edible plants, the leaves of strawberry and coriander plants were bright green, while those of purple rape were dark purple; thus, we suspected that changes in cortisol in this study might be closely related to green color. The green color of plants can be sensed by ipRGCs and projected to the paraventricular nucleus of the hypothalamus, which may downregulate cortisol secretion by stimulating the adrenal gland. Studies have shown that the green color of plants could restore mental state and relieve work stress of workers (Kim and Mattson, 1998). Green plants produce positive attitude and promote brain function (Jang et al. 2014). In addition, humans receive information from the environment through five senses but most (more than 70%) occurring through visual perception (Whang et al., 1997). Therefore, this may be the most important reason why strawberry and coriander, which have green-colored leaves, could reduce cortisol concentrations. Moreover, the warm light environment might regulate the hypothalamus to reduce the release of cortisol (Bedrosian et al., 2013). However, the color temperature of the light environment was rarely studied in previous studies, and the underlying 15

molecular mechanism remains unclear. Hence, this remains to be confirmed with more evidence. Apart from the green leaves, strawberry also had white and yellow flowers, and subjective emotion improvement of participants under the stimulus with strawberry was more obvious than that using coriander. The results of subjective emotions of each volunteer are presented herein, with a similar trend (Figures A2 and A3). Thus, the white and yellow colors might also have had a positive effect on emotion; previous studies have reported similar results that white and yellow stimuli provided feelings of ease, brightness, and warmth (Jang et al., 2014). Subjects who performed a transplanting activity with real flowers showed a better emotional condition than those transplanting with artificial flowers (Lee et al., 2013). Therefore, the fragrance of real plants also could bring pleasure to human (Lee et al., 2013). Fragrance was an important factor in emotion regulation because the olfactory system is closely connected to the emotion regions of the brain (Brennan and Keverne, 1990; Herz et al., 2004b). The fragrance of the Japanese citrus fruit Yuzu might alleviate negative emotional stress, which, at least in part, would contribute to the suppression of sympathetic nervous system activity (Matsumoto and Asakura, 2014). Odors of food (strawberry, orange, and mango) activated the dopaminergic pathways in the brain more than nonfood odors (lily of the valley, jasmine, and lavender) (Frasnelli et al., 2015). Our study showed that the effect of coriander stimulus on subjective emotion regulation was not as 16

obvious as that of strawberry, which might be due to the different fragrances. However, this remains to be confirmed with more evidence. Although improvement in the subjective emotions under coriander stimulus was not that obvious as that of strawberry, coriander could evidently improve the sleep condition of volunteers in the isolated environment in our study. Figure A4 shows that improvement in the sleep condition of the four participants under coriander stimulus and a warm light environment was more pronounced than that in other treatments. In the field of traditional Chinese medicine, fresh juice of coriander leaves and the essential oils of its seeds are often used to relieve anxiety and insomnia (Shahwar et al., 2012). Previous animal experiments confirmed the sedative and hypnotic function of coriander essential

oil

(Emamghoreishi

and

Heidari-Hamedani,

2006).

Several

compounds in coriander seed may account for such sedative activity, including flavonoids, quercetin, and isoquercitrin. A sedative effect has been shown with quercetin as well as quercitrin and isoquercitrin glycosides isolated from Albizia julibrissin (Avallone et al., 2000; Kang et al., 2000). The results of this study indicated that coriander could reduce sleep latency obviously than purple rape and strawberry. We suspected that the volatile compounds of coriander play a main role in reducing anxiety and promoting sleep. However, the regulation mechanism of human sleep by coriander plants in an isolated environment remains unclear, and further research is needed.

17

In addition, light environment contributed much to improve sleep in our study. The impact of light environment on sleep has always been a hot topic. In last decades, studies have confirmed that light environment could affect sleep quality by inhibiting melatonin secretion at night (Hashimoto et al., 1996). Melatonin is an important hormone that can promote sleep (Dawson and Encel, 1993). Light environment with a higher color temperature might tend to inhibit melatonin secretion at night than that with a lower color temperature. Therefore, exposure to a higher color temperature before going to bed often causes sleep problems such as decreased sleep quality and increased sleep latency (Hashimoto et al., 1996). Exposure to a light environment with high color temperature in the nighttime would enhance the activity of the sympathetic nervous system (Tsutsumi et al., 2002) and increase alertness (Vetter et al., 2011). The results of this study showed that volunteers exposed to the light environment with 3000 K color temperature before bedtime had higher sleep efficiency as well as lower sleep latency and micro-awakening index than those exposed to other light environments in an isolated environment. The results of each individual are given in the supplementary document (Figure A4). We also examined the efferent of different light environments on heart rate and duration of the REM period. The results showed that the light environment with 3000 K color temperature could reduce heart rate during the REM period and increase the duration of the REM period, but the differences were not significant. Our results, consistent with the 18

previous reports, show that higher color temperatures were not beneficial for sleep. Emotion is closely related to sleep. Emotional events have an impact on the quality of our sleep. Reported effects of pre-sleep emotion on sleep include increased or decreased latency to REM sleep as well as increased REM density and REM sleep duration (Perlis and Nielsen, 1993). Occurrence of arousals in sleep was taken as a marker of sleep disruption as well as disturbances in sleep continuity (Halász and Bódizs, 2004). Furthermore, the way sleep impacted next-day emotion was thought to be particularly affected through REM sleep (Beattie et al., 2015; Walker and Van, 2009). The correlation between emotion and sleep was also analyzed in our study. Table A1 shows that hostility and stress are positively correlated to REM latency and micro-awakening index, similar to previous reports. We also found that there was a positive correlation between vigor and sleep latency, suggesting that excitement may lengthen the time to sleep. Therefore, exposure to “warm” light environments together with coriander or strawberry stimulus before bedtime could improve the quality of sleep, which might be due to the fragrance of coriander and emotional regulation of strawberry. 4. Conclusion This study supported the fact that horticultural activities and exposure to light environments could enhance not only emotion but also sleep quality in an isolated environment. Particularly, strawberry could improve emotion by 19

improving positive feelings, and coriander could reduce sleep latency and REM latency. Further, we observed a synergistic effect of edible plants with different light environments on the sleep latency and REM latency. However, our study had two limitations. First, the sample size was small. Hence, future studies should recruit more subjects to further analyze the specific physiological mechanism underlying the stimulation by edible plants. Second, we used a portable PSG device to detect sleep quality with limited accuracy; hence, in future research, EEG signals should be recorded using 64 channels. Acknowledgments The authors express their deepest thanks to all study participants. This work was financially supported by grants from the National Natural Science Foundation of China (81871520) and China Postdoctoral Science Foundation (2019M650445). Conflict of interest The authors confirm that this paper has never been submitted to other journals and that the original results are reliable and credible. They declare no conflicts of interest.

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Figure legends

28

Figure 1. Experiment timeline of this research. The experiment was carried out

at

the

third

phase

of

the

“lunar

palace

365”

experiment

(2018.1.26-2018.5.15), and the pink part was the time range of the texts (2018.3.22-2018.4.22). When the tests began, volunteers had already lived in an isolated environment for 56 days.

Figure 2. Overview of the protocol. Two orthogonal factors: edible plants (purple rape, coriander, and strawberry) and light environment (3000 K, 4500 K, and 6000 K color temperature) (a); The protocol of the overall experimental (b): after preparing and relaxing for 7 minutes, the volunteers answered the 29

POMS and PANAS questionnaires for 4 minutes, followed by watching and touching edible plants in different light environments; subsequently, the volunteers spent 8 hours to sleep in the dark; finally, volunteers answered the POMS and PANAS questionnaires when they woke up the next morning. Black arrow indicates the collection of saliva samples.

Figure 3. Changes in salivary cortisol levels (

) under different stimuli

(mean ± SD). Data presented as variation ± standard error (N = 4). P, Purple rape; C, Coriander; S, Strawberry. Friedman tests were used to assess the main effects of edible plants. Wilcoxon’s signed-rank tests were used to identify the significant differences between the three kinds of edible plants.

30

Figure 4. Scores of PANAS under different stimuli (means ± SD). Data presented as variation ± standard error (N = 4). Friedman tests were used to assess the main effects of edible plants. Wilcoxon’s signed-rank tests were used to identify the significant differences between the three kinds of edible plants.

31

Figure 5. (a) Subscale scores for the profile of mood states (POMS) scale under different stimuli (mean ± SD). T-A, tension-anxiety; A-H, anger-hostility; F, fatigue; D, dejection; C, confusion; V, vigor; S-E, self-esteem; (b) Comparisons of the total mood disturbance (TMD) score in the profile of mood state (POMS) questionnaire under different conditions. Data presented as variation ± standard error (N = 4). Friedman tests were used to assess for the main effects of edible plants for emotion. Wilcoxon’s signed-rank tests were used to identify the significant differences between the three kinds of edible plants.

⁎

Difference between the three edible plants was statistically significant

at (P<0.05).

32

Figure

6.

Comparisons

of

sleep

latency

(a),

REM

latency

(b),

Micro-awakening index (c), and sleep efficiency (d) between different combinations of edible plants and light environment (mean ± SD). Friedman tests were used to assess the main effects of edible plants for sleep latency, micro-awakening index, REM latency, and sleep efficiency. Wilcoxon’s signed-rank tests were used to identify the significant differences between the three kinds of edible plants.

⁎

Difference between the three edible plants was

statistically significant at P<0.05.

33