Acute stress does not affect economic behavior in the experimental laboratory.

We report statistical results from a laboratory experiment in which participants were required to make decisions with monetary consequences in several solitary and interactive situations under acute stress. Our study follows the tradition of behavioral and experimental economics in selecting the experimental situations and incorporates elements from medical and psychological research in the way stress is induced and measured. It relies on a larger sample, with 192 volunteers, than previous studies to achieve higher statistical power. The main conclusion, drawn from binary comparisons between the treatment and reference groups, is that acute stress does not have a significant impact on cognitive skills, strategic sophistication, risk attitudes, altruism, cooperativeness, or nastiness. Regression analysis, controlling for psycho-social characteristics, corroborates these findings, while also suggesting that acute stress significantly decreases men's risk aversion (as measured by a lottery-choice risk-elicitation task).

Prolonged Effects of Acute Stress on Decision-Making under Risk: A Human Psychophysiological Study.

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 h 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.

Serotonin transporter gene polymorphism modulates inflammatory cytokine responses during acute stress.

Cytokines are important mediators of various stress-related modulations of immune function. A major genetic factor determining inter-individual differences in stress reactivity is polymorphisms of the serotonin (5-hydroxytryptamine, 5HT) transporter (5HTT) gene. A short (S) variant, compared with a long (L) variant, of the promoter region of the 5HTT gene-linked polymorphic region (5HTTLPR) has been related to emotional and stress hyper-reactivity. The present study examined whether the 5HTTLPR can modulate responses of inflammatory cytokines under acute stress. Nine Japanese male participants carrying two copies of the S alleles and nine Japanese males carrying S and L alleles underwent the Trier Social Stress Test (TSST). Inflammatory cytokines, endocrine parameters, heart rate and subjective stress were measured before, during and after the task. The participants carrying the SS alleles, but not those carrying the SL alleles, showed a significant increase of IL-1ß immediately after TSST. This hyper-reactivity to acute stress in individuals with the SS alleles was also observed in their heart rate and cortisol levels. These results suggest that the S allele of the 5HTTLPR is consistently associated with stress reactivity in multi-level stress-related biological systems.

Genetic variations in the human cannabinoid receptor gene are associated with happiness.

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.

Brain-immune interaction accompanying odor-evoked autobiographic memory.

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.

Pro-inflammatory cytokine predicts reduced rejection of unfair financial offers.

OBJECTIVES: This study aimed to examine one of biological correlates, pro-inflammatory cytokine, in rejection of unfair financial offers in the Ultimatum Game (UG), where the division of a sum of money is proposed and the player can accept or reject this offer. METHODS: Nineteen participants played 20 trials of the UG as responders, and they were proposed unfair offers in a half of the trials. Baseline levels of several pro-inflammatory and anti-inflammatory cytokines, subjective happiness, and depression of them were measured. RESULTS: Participants with higher levels of the pro-inflammatory cytokine, interleukin (IL)-6 rejected fewer unfair offers. This effect of IL-6 levels on decision-making was independent from other pro-inflammatory cytokines, anti-inflammatory cytokines, subjective happiness, and depression. CONCLUSIONS: These results suggested that chronic higher levels of IL-6 might affect functions of neural regions related to decision making, and thus can modulate rejection of unfair offers.

Executive functioning performance predicts subjective and physiological acute stress reactivity: preliminary results.

Individual differences in baseline executive functioning (EF) capacities have been shown to predict state anxiety during acute stressor exposure. However, no previous studies have clearly demonstrated the relationship between EF and physiological measures of stress. The present study investigated the efficacy of several well-known EF tests (letter fluency, Stroop test, and Wisconsin Card Sorting Test) in predicting both subjective and physiological stress reactivity during acute psychosocial stress exposure. Our results show that letter fluency served as the best predictor for both types of reactivity. Specifically, the higher the letter fluency score, the lower the acute stress reactivity after controlling for the baseline stress response, as indicated by lower levels of state anxiety, negative mood, salivary cortisol, and skin conductance. Moreover, the predictive power of the letter fluency test remained significant for state anxiety and cortisol indices even after further adjustments for covariates by adding the body mass index (BMI) as a covariate. Thus, good EF performance, as reflected by high letter fluency scores, may dampen acute stress responses, which suggests that EF processes are directly associated with aspects of stress regulation.

Association between perceived happiness levels and peripheral circulating pro-inflammatory cytokine levels in middle-aged adults in Japan.

OBJECTIVES: The idea that perceived happiness may be associated with health and well-being is a recent topic of focus. However, the neurobiological mechanisms underlying the positive effects of happiness on psychological and physiological wellness remain obscure. In this study, we attempted to clarify the association between systemic inflammation and happiness. METHODS: We recruited 160 healthy volunteers for experiment 1 and compared peripheral inflammatory markers, namely the concentrations of pro-inflammatory cytokines in the serum, between perceived high-happiness and low-happiness groups. Subsequently, we recruited 7 romantic couples for experiment 2 and investigated changes in peripheral pro-inflammatory cytokine levels after the evocation of happiness, which was induced by warm physical contact with the partner. RESULTS: We found that circulating levels of interferon-γ (IFN-γ), which can affect brain functions and induce depressive symptoms, were lower in the high-happiness group than in the low-happiness group. A negative correlation between the levels of perceived happiness and IFN-γ concentrations was also observed. Furthermore, we also found that experimentally induced happiness could reduce peripheral IFN-γ levels. CONCLUSIONS: These results revealed an association between the perception of happiness and systemic inflammation. Increased happiness may suppress the peripheral circulation of pro-inflammatory cytokines.

Psychological and physiological responses to odor-evoked autobiographic memory.

OBJECTIVE: The "Proust phenomenon" occurs when a certain smell evokes a specific memory. Recent studies have demonstrated that odor-evoked autobiographic memories are more emotional than those elicited by other sensory stimuli because of the direct neural communication between the olfactory system and the amygdala. The amygdala is known to regulate various physiological activities including the endocrine and immune systems; therefore, odor-evoked autobiographic memory may trigger various psychological and physiological responses; however, the responses elicited by this memory remains obscure. In this study, we aimed to investigate the psychological and physiological responses accompanying odor-evoked autobiographic memory. METHODS: We recruited healthy male and female volunteers and investigated changes in their mood states and autonomic nervous, endocrine, and immune activities when autobiographic memory was evoked in the participants by asking them to smell an odor(s) that was nostalgic to them. RESULTS: The autobiographic memories associated with positive emotion resulted in increased positive mood states, such as comfort and happiness, and decreased negative mood states, such as anxiety. Furthermore, heart rate was decreased, skin-conductance level was increased, and peripheral interleukin-2 level was decreased after smelling the nostalgic odor. These psychological and physiological responses were significantly correlated. CONCLUSIONS: The present study suggests that odor-evoked autobiographic memory along with a positive feeling induce various physiological responses, including the autonomic nervous and immune activities. To the best of our knowledge, the present study is the first to observe an interaction between odor-evoked autobiographic memories and immune function.

Genetic variations in the serotonin transporter gene-linked polymorphic region influence attraction for a favorite person and the associated interactions between the central nervous and immune systems.

Limbic system activation that occurs when a person experiences several emotions is primarily represented by the amygdala output that influences autonomic brainstem nuclei that control autonomic nervous function, thus modulating the endocrine and immune systems. Amygdala activity is modulated by the serotonin transporter gene-linked polymorphic region (5HTTLPR); however, whether variations in 5HTTLPR influence central nervous and immune activities in response to positive stimuli remains unclear. Here, we found that seeing a favorite person induced significantly higher amygdala activity in individuals with the 5HTTLPR SS genotype than in others. This activity was positively correlated with changes in the NK cell proportion among peripheral lymphocytes. Thus, 5HTTLPR influences attraction and the associated interactions between the central nervous and immune systems in affectively positive situations.

Transient responses of inflammatory cytokines in acute stress.

It has been demonstrated that concentrations of pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) are elevated by acute stress. Although several studies confirmed robust changes in IL-6, how acute stress affects other cytokines was less clear. Therefore, the present study simultaneously examined the effects of acute stress on several pro-inflammatory cytokines. Sixteen male participants were given the Trier Social Stress Test (TSST). Blood samples were collected at baseline, immediately after, and 30, 60, and 90min after the TSST. IL-1beta significantly increased immediately after the TSST and returned to the baseline level after 30min. Additionally, this elevation of IL-1beta was correlated with the perceived intensity of stress. These results showed that the concentration of IL-1beta is rapidly regulated, and that elevation of the IL-1beta level could possibly be attributed to transient mobilization of monocytes caused by sympathetic nervous activation. Moreover, a transient increase of IL-1beta might be conveyed to the brain and play a role in forming negative emotional states.