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Abstract Background The coronavirus disease 2019 (COVID-19) pandemic has greatly changed our daily life. Owing to the imposed restrictions, many educational facilities have introduced remote teaching. This study aims to clarify the association between remote teaching and Japanese university students' sleeping habits. Methods The participants were medical students at Aichi Medical University. We used data from an ongoing longitudinal sleeping habits survey. For the participants who enrolled in the university during 2018–2020, multilevel analyses of sleep duration during weekdays and weekends across 3 years were conducted, adjusting for sex, grade, place of stay, sleep problems and lifestyle habits. Results Among the students enrolled in the university, the data of 677 in 2018, 657 in 2019, and 398 in 2020 was available for analysis. The mean sleep duration during weekdays (in minutes) was 407.6 ± 60.3 in 2018, 406.9 ± 63.0 in 2019, and 417.3 ± 80.9 in 2020. The mean sleep duration during weekends (in minutes) was 494.5 ± 82.5 in 2018, 488.3 ± 87.9 in 2019, and 462.3 ± 96.4 in 2020. Multilevel analysis conducted for the 684 participants who enrolled during 2018–2020 showed that sleep duration during weekdays was associated with the place of stay and survey year. Moreover, students reported significantly longer sleep duration during weekdays in 2020 than in 2019, but no significant difference in sleep duration was found between 2018 and 2019. The other multilevel analysis found sleep duration during weekends to be associated with the survey year, sex and always doing something before going to bed. Sleep duration during weekends was shorter in 2020 than in 2019 and longer for male students and students who always do something before going to bed. Ten students were reported to have a delayed sleep phase in 2020. Conclusions Students' sleep duration increased during weekdays and decreased during weekends in 2020. This difference could be explained by the COVID-19 pandemic and the introduction of remote teaching.

Studies on the association between trust and oxytocin, a neuropeptide of the central nervous system, have not reached a consensus, thereby challenging the possibility of a direct association between the two. However, previous studies have not examined how oxytocin is correlated with trust, based on its categorization into different factors in the field of social science. For instance, based on Yamagishi's trust theory, trust can be categorized into two factors: general trust and caution. General trust refers to beliefs about the trustworthiness of others, whereas caution refers to the belief that caution is needed when dealing with high social uncertainty. In this study, to examine the relationship between these two factors and oxytocin, we analyzed data of 197 adults (men = 98, women = 99; mean age = 41.7 years; standard deviation for age = 10.4 years) and examined the relationships between these two factors of trust and endogenous salivary oxytocin levels. We found that oxytocin was positively correlated with caution rather than with general trust thereby suggesting that oxytocin plays a role in regulating caution rather than general trust among the components of trust. The present study demonstrated that salivary oxytocin level can act as a biomarker that partially predicts one's trust, especially as reflected by caution.

Previous studies in population genetics have proposed that the Y-chromosomal (Y-DNA) haplogroup D ancestor likely originated from Africa. The haplogroup D branch next started Out-of-Africa migration, rapidly expanded across Eurasia, and later diversified in East Asia. Y-DNA haplogroup D-M55, one of the branches of haplogroup D, is only found in modern Japanese males, suggesting that individuals with Y-DNA haplogroup D migrated from the Eurasian continent. Based on previous observations, Y-DNA haplogroup D is expected to be associated with some male characteristics including personality. Therefore, this study investigated whether the Y-DNA haplogroup D-M55 is associated with several physiological and psychological characteristics, including exploratory motivation and human relationship-related perception. We recruited Japanese young adult males and females and investigated the association between Y-DNA haplogroup D-M55, physiological [body mass index (BMI)], and several psychological parameters [perceived number of close friends, behavioral inhibition system/behavioral activation system (BIS/BAS), perceived happiness, and perceived loneliness]. The results indicated that males with haplogroup D-M55 had a higher BMI and more close friends, compared with non-carrier males. Additional multiple regression analyses, which tested the hypothesis that haplogroup D-M55 predicts BMI and perceived number of close friends, confirmed our hypothesis, even after controlling for the potentially confounding variables of age and sex. We also analyzed the gene–gene interaction between haplogroup D-M55 and an autosomal gene polymorphism associated with BMI and human relationships, such as the dopamine D2 receptor gene (DRD2: rs1800497). Results showed gene–gene interactions between haplogroups D-M55 and DRD2 in BMI. Based on these findings, it is demonstrated that Y-DNA haplogroup D is associated with human personality.

Spirituality and religiosity have a significant impact on one's well-being. Although previous studies have indicated that the neuropeptide hormone oxytocin is associated with spirituality/religiosity, existing findings remain inconsistent. Some studies have reported a positive relationship between oxytocin and spirituality/religiosity, while other studies have reported a negative association. Herein, we examined the association between endogenous oxytocin and spirituality/religiosity in 200 non-Abrahamic Japanese individuals (102 females, mean age ± standard deviation = 41.53 ± 10.46) by measuring the level of salivary oxytocin and spiritual/religious faith. We found that the level of salivary oxytocin was negatively associated with spiritual/religious faith. Individuals with higher levels of salivary oxytocin tend to have more negative spiritual/religious faith compared with those with low oxytocin levels (e.g., “Spirituality/religiosity makes people passive and clinging.”). Moreover, this tendency was only significant in individuals who were not interested in a specific religion. The uniqueness of spirituality/religiosity in Japan could help interpret the current findings.

Prior research has found that East Asians are less willing than Westerners to seek social support in times of need. What factors account for this cultural difference? Whereas previous research has examined the mediating effect of relational concern, we predicted that empathic concern, which refers to feeling sympathy and concern for people in need and varies by individuals from different cultures, would promote support seeking. We tested the prediction in two studies. In Study 1, European Canadians reported higher empathic concern and a higher frequency of support seeking, compared to the Japanese participants. As predicted, cultural differences in social support seeking were influenced by empathic concern. In Study 2, both empathic concern and relational concern mediated cultural differences in support seeking. Japanese with lower empathic concern but higher relational concern were more reluctant than European Americans to seek social support during stressful times. Finally, loneliness, which was more prevalent among the Japanese than among the European Americans, was partially explained by social support seeking.

Hinoki cypress (Chamaecyparis obtusa) shows durability against termites and wood decay-causing fungi and is used as a construction material in Japan. However, the effects of the material are still not fully understood. The aim of this study was to evaluate whether Hinoki cypress has antimicrobial effects against airborne microorganisms. We examined the influence of Hinoki cypress on the growth of airborne bacteria and fungi using culture-based methods. The growth of bacterial colonies was observed after day 3 in the control group without Hinoki material. In contrast, the growth of bacterial colonies was observed after day 13 in the experimental group containing Hinoki material. In the experimental group, the number of fungal colonies was smaller than that in the control group, suggesting the antifungal effect of Hinoki cypress to some extent. In addition, we characterized the community structure of airborne bacteria in two rooms with and without cypress wood by the culture-independent method of PCR-denaturing gradient gel electrophoresis. This also suggested differences in the community structure of airborne bacteria depending on the presence or absence of Hinoki cypress wood. These results indicate that Hinoki cypress might be a useful functional material in building environments.

Previous studies have shown that a cytosine (C) to thymine (T) single nucleotide polymorphism (SNP) of the human cannabinoid receptor 1 (CNR1) gene is associated with positive emotional processing. C allele carriers are more sensitive to positive emotional stimuli including happiness. The effects of several gene polymorphisms related to sensitivity to emotional stimuli, such as that in the serotonin transporter gene-linked polymorphic region (5HTTLPR), on emotional processing have been reported to differ among cultures-e.g., between those that are independent and interdependent. Thus, we postulated that the effects of the CNR1 genotype on happiness might differ among different cultures because the concept of happiness varies by culture. We recruited healthy male and female young adults in Japan, where favorable external circumstances determine the concept of happiness, and Canada, where the concept of happiness centers on positive inner feelings, and compared the effects of the CNR1 genotype on both subjective happiness levels (self-evaluation as being a happy person) and situation-specific happiness (happy feelings accompanying various positive events) by using a questionnaire. We found that the effect of CNR1 on subjective happiness was different between the Japanese and Canadian groups. The subjective happiness level was the highest in Japanese individuals with the CC genotype, whereas in Canadian participants, it was the highest in individuals with the TT genotype. Furthermore, the effects of CNR1 genotype on situation-specific happiness were also different between the groups. Happiness accompanied with being surrounded by happy people was the highest among Japanese individuals with the CC genotype, whereas among Canadian individuals, it was the highest in TT genotype carriers. These findings suggest that culture and CNR1 polymorphism interact to influence the perception of happiness.

Happiness is regarded as one of the most fundamental human goals. Given recent reports that positive feelings are contagious (e.g., the presence of a happy person enhances others' happiness) because of the human ability to empathize (i.e., sharing emotions), empathic ability may be a key factor in increasing one's own subjective level of happiness. Based on previous studies indicating that a single nucleotide polymorphism in the serotonin 2A receptor gene [HTR2A rs6311 guanine (G) vs. adenine (A)] is associated with sensitivity to emotional stimuli and several mental disorders such as depression, we predicted that the polymorphism might be associated with the effect of sharing happiness. To elucidate the neural and genetic correlates of the effect of sharing happiness, we first performed functional magnetic resonance imaging (fMRI) during a “happy feelings” evocation task (emotional event imagination task), during which we manipulated the valence of the imagined event (positive, neutral, or negative), as well as the presence of a friend experiencing a positive-valence event (presence or absence). We recruited young adult women for this fMRI study because empathic ability may be higher in women than in men. Participants felt happier (p < 0.01) and the mentalizing/theory-of-mind network, which spans the medial prefrontal cortex, temporoparietal junction, temporal poles, and precuneus, was significantly more active (p < 0.05) in the presence condition than in the absence condition regardless of event valence. Moreover, participants with the GG (p < 0.01) and AG (p < 0.05) genotypes of HTR2A experienced happier feelings as well as greater activation of a part of the mentalizing/theory-of-mind network (p < 0.05) during empathy for happiness (neutral/presence condition) than those with the AA genotype. In a follow-up study with a vignette-based questionnaire conducted in a relatively large sample, male and female participants were presented with the same imagined events wherein their valence and the presence of a friend were manipulated. Results showed genetic differences in happiness-related empathy regardless of sex (p < 0.05). Findings suggest that HTR2A polymorphisms are associated with the effect of sharing happiness by modulating the activity of the mentalizing/theory-of-mind network.

Although human saliva contains the monoamine serotonin, which plays a key role in the modulation of emotional states, the association between salivary serotonin and empathic ability remains unclear. In order to elucidate the associations between salivary serotonin levels, trait empathy, and the sharing effect of emotions (i.e., sharing emotional experiences with others), we performed a vignette-based study. Participants were asked to evaluate their happiness when they experience several hypothetical life events, whereby we manipulated the valence of the imagined event (positive, neutral, or negative), as well as the presence of a friend (absent, positive, or negative). Results indicated that the presence of a happy friend significantly enhanced participants' happiness. Correlation analysis demonstrated that salivary serotonin levels were negatively correlated with happiness when both the self and friend conditions were positive. Correlation analysis also indicated a negative relationship between salivary serotonin levels and trait empathy (particularly in perspective taking), which was measured by the Interpersonal Reactivity Index. Furthermore, an exploratory multiple regression analysis suggested that mothers' attention during childhood predicted salivary serotonin levels. Our findings indicate that empathic abilities and the social sharing of happiness decreases as a function of salivary serotonin levels.

Hypofrontality is a state of decreased cerebral blood flow in the prefrontal cortex during executive function performance; it is commonly observed in patients with schizophrenia. Cognitive dysfunction, as well as the psychological symptoms of schizophrenia, influences the ability of patients to reintegrate into society. The current study investigated the effects of an interactive sports video game (IVG; Nintendo Wii™ Sports Resort) on frontal lobe function of patients with schizophrenia. A sample of eight patients (6 male and 2 female; mean age = 46.7 years, standard deviation (SD) = 13.7) engaged in an IVG every week for 3 months in a controlled, single-blind, crossover study. Before and after the intervention we examined frontal lobe blood-flow volume using functional near-infrared spectroscopy (fNIRS), and assessed functional changes using the Frontal Assessment Battery, Health-Related Quality of Life scale, and behaviorally-assessed physical function tests. fNIRS revealed that prefrontal activity during IVG performance significantly increased in the IVG period compared with the control period. Furthermore, significant correlations between cerebral blood flow changes in different channels were observed during IVG performance. In addition, we observed intervention-related improvement in health-related quality of life following IVG. IVG intervention was associated with increased prefrontal cortex activation and improved health-related quality of life performance in patients with schizophrenia. Patients with chronic schizophrenia are characterized by withdrawal and a lack of social responsiveness or interest in others. Interventions using IVG may provide a useful low-cost rehabilitation method for such patients, without the need for specialized equipment.

Romantic relationship, a widespread feature of human society, is one of the most influential factors in daily life. Although stimuli related to romantic love or being in a romantic relationship commonly result in enhancement of activation or functional connectivity of the reward system, including the striatum, the structure underlying romantic relationship-related regions remain unclear. Because individual experiences can alter gray matter within the adult human brain, we hypothesized that romantic relationship is associated with structural differences in the striatum related to the positive subjective experience of being in a romantic relationship. Because intimate romantic relationships contribute to perceived subjective happiness, this subjective enhancement of happiness might be accompanied by the experience of positive events related to being in a romantic relationship. To test this hypothesis and elucidate the structure involved, we compared subjective happiness, an indirect measure of the existence of positive experiences caused by being in a romantic relationship, of participants with or without romantic partners (N = 68). Furthermore, we also conducted a voxel-based morphometry (VBM) study of the effects of being in a romantic relationship (N = 113). Being in a romantic relationship was associated with greater subjective happiness and reduced gray matter density within the right dorsal striatum. These results suggest that being in a romantic relationship enhances perceived subjective happiness via positive experiences. Furthermore, the observed reduction in gray matter density in the right dorsal striatum may reflect an increase in saliency of social reward within a romantic relationship. Thus, being in a romantic relationship is associated with positive experiences and a reduction of gray matter density in the right dorsal striatum, representing a modulation of social reward.

This study investigates the prolonged effects of physiological responses induced by acute stress on risk-taking in decision-making. Participants were divided into a Stress group (N = 14) and a Control group (N = 12). The Trier Social Stress Test was administered as an acute stressor, and reading was administered as a control task; thereafter, participants performed a decision-making task in which they needed to choose a sure option or a gamble option in Gain and Loss frame trials 2 hours after (non-) exposure to the stressor. Increased cortisol, adrenaline, heart rate (HR), and subjective stress levels validated acute stress manipulation. Stressed participants made fewer risky choices only in the Gain domain, whereas no effect of stress was shown in the Loss domain. Deceleration of HR reflecting attention was greater for Gains compared with Losses only in the Stress group. Risk avoidance was determined by increased levels of cortisol caused by acute stress. These results suggest that processes regarding glucocorticoid might be involved in the prolonged effects of acute stress on the evaluation of risks and the monitoring of outcomes in decision-making.

Recent studies indicate that patients with depression have increased concentrations of serum pro-inflammatory cytokines. However, studies of IL-17 and studies on community-dwellers are few. The purpose of this study was to investigate serum cytokine levels, especially IL-17A, among subjects with high and low depressive symptoms of a general population. The participants comprised 20 female community-dwellers aged 40 years or older who contributed to a Shika study in Ishikawa, Japan. Ten participants who showed higher and ten who showed lower depressive symptoms among 208 females assessed by the Japanese version of the Centre for Epidemiologic Studies Depression Scale (CES-D) were selected for this study. Serum samples were analyzed for TNF-alpha, IL-6, IL-10, IL-12, and IL-17A using a multiplex Luminex analysis. For the comparison between the high and low depressive groups statistically, linear regression analyses were applied. The serum level of IL-17A was significantly higher among the high depressive participants (p < 0.05) even after controlling possible confounders, whereas there were no differences in TNF-alpha, IL-6, IL-10, or IL-12 between the high and low depressive groups. Our findings supported an association between serum IL-17A levels and depressive symptoms. Peripheral IL-17A immune response may be a preventive and treatment target for depression.

Happiness has been viewed as a temporary emotional state (e.g., pleasure) and a relatively stable state of being happy (subjective happiness level). As previous studies demonstrated that individuals with high subjective happiness level rated their current affective states more positively when they experience positive events, these two aspects of happiness are interrelated. According to a recent neuroimaging study, the cytosine to thymine single-nucleotide polymorphism of the human cannabinoid receptor 1 gene is associated with sensitivity to positive emotional stimuli. Thus, we hypothesized that our genetic traits, such as the human cannabinoid receptor 1 genotypes, are closely related to the two aspects of happiness. In Experiment 1, 198 healthy volunteers were used to compare the subjective happiness level between cytosine allele carriers and thymine-thymine carriers of the human cannabinoid receptor 1 gene. In Experiment 2, we used positron emission tomography with 20 healthy participants to compare the brain responses to positive emotional stimuli of cytosine allele carriers to that of thymine-thymine carriers. Compared to thymine-thymine carriers, cytosine allele carriers have a higher subjective happiness level. Regression analysis indicated that the cytosine allele is significantly associated with subjective happiness level. The positive mood after watching a positive film was significantly higher for the cytosine allele carriers compared to the thymine-thymine carriers. Positive emotion-related brain region such as the medial prefrontal cortex was significantly activated when the cytosine allele carriers watched the positive film compared to the thymine-thymine carriers. Thus, the human cannabinoid receptor 1 genotypes are closely related to two aspects of happiness. Compared to thymine-thymine carriers, the cytosine allele carriers of the human cannabinoid receptor 1 gene, who are sensitive to positive emotional stimuli, exhibited greater magnitude positive emotions when they experienced positive events and had a higher subjective happiness level.

The reputation of others influences partner selection in human cooperative behaviors through verbal reputation representation. Although the way in which humans represent the verbal reputations of others is a pivotal issue for social neuroscience, the neural correlates underlying the representation of verbal reputations of others are unclear. Humans primarily depend on self-evaluation when assessing reputation of self. Likewise, humans might primarily depend on self-evaluation of others when representing their reputation. As interaction promotes the formation of more nuanced, individualized impressions of an interaction partner, humans tend to form self-evaluations of persons with whom they are intimate in their daily life. Thus, we hypothesized that the representation of reputation of others is modulated by intimacy due to one's own evaluation formation of that person. To test this hypothesis, we conducted a functional magnetic resonance imaging experiment with 11 pairs of romantic partners while they viewed an evaluation of a target person (self, partner [intimate other], or stranger [non-intimate other]), made by other evaluators. When compared with strangers, viewing evaluations of self and partner activated overlapping regions in the medial prefrontal cortex. Verbal reputation of self-specific activation was found in the precuneus, which represents self-related processing. The data suggest that midline structures represent reputation of self. In addition, intimacy-modulated activation in the medial prefrontal cortex suggests that the verbal reputation of intimate others is represented similarly to reputation of self. These results suggest that the reputation representation in the medial prefrontal cortex is engaged by verbal reputation of self and intimate others stemming from both own and other evaluators' judgments.

The phenomenon in which a certain smell evokes a specific memory is known as the Proust phenomenon. Odor-evoked autobiographic memories are more emotional than those elicited by other sensory stimuli. The results of our previous study indicated that odor-evoked autobiographic memory accompanied by positive emotions has remarkable effects on various psychological and physiological activities, including the secretion of cytokines, which are immune-signaling molecules that modulate systemic inflammation. In this study, we aimed to clarify the neural substrates associated with the interaction between odor-evoked autobiographic memory and peripheral circulating cytokines. We recruited healthy male and female volunteers and investigated the association between brain responses and the concentration of several cytokines in the plasma by using positron emission tomography (PET) recordings when an autographic memory was evoked in participants by asking them to smell an odor that was nostalgic to them. Participants experienced positive emotions and autobiographic memories when nostalgic odors were presented to them. The levels of peripheral proinflammatory cytokines, such as the tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), were significantly reduced after experiencing odor-evoked autobiographic memory. Subtraction analysis of PET images indicated that the medial orbitofrontal cortex (mOFC) and precuneus/posterior cingulate cortex (PCC) were significantly activated during experiences of odor-evoked autobiographic memory. Furthermore, a correlation analysis indicated that activities of the mOFC and precuneus/PCC were negatively correlated with IFN-γ concentration. These results indicate that the neural networks including the precuneus/PCC and mOFC might regulate the secretion of peripheral proinflammatory cytokines during the experience of odor-evoked autobiographic memories accompanied with positive emotions.

Mindfulness is currently attracting a great deal of attention as a psychotherapy technique. It is defined as bringing one's complete attention to the experiences occurring in the present moment in a nonjudgmental or accepting way. The Five Facet Mindfulness Questionnaire (FFMQ) was developed to assess individual differences in mindfulness states. The FFMQ is composed of five facets representing elements of mindfulness: non-reactivity to inner experience, non-judging, acting with awareness, describing, and observing. In the present study, we applied voxel-based morphometry to investigate the relationship between the brain structure and each facet as measured by the FFMQ. The results showed a positive association between the describing facet of mindfulness on the FFMQ and gray matter volume in the right anterior insula and the right amygdala. In conclusion, mindfulness was related with development in parts of the somatic marker circuit of the brain.