Kenta Kimura

Kwansei Gakuin University, Nishinomiya, Hyōgo, Japan

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Publications (4)15.83 Total impact

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    ABSTRACT: Motivation is well known to enhance working memory (WM) capacity, but the mechanism underlying this effect remains unclear. The WM process can be divided into encoding, maintenance, and retrieval, and in a change detection visual WM paradigm, the encoding and retrieval processes can be subdivided into perceptual and central processing. To clarify which of these segments are most influenced by motivation, we measured ERPs in a change detection task with differential monetary rewards. The results showed that the enhancement of WM capacity under high motivation was accompanied by modulations of late central components but not those reflecting attentional control on perceptual inputs across all stages of WM. We conclude that the "state-dependent" shift of motivation impacted the central, rather than the perceptual functions in order to achieve better behavioral performances.
    Psychophysiology 07/2013; · 3.29 Impact Factor
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    ABSTRACT: Although interleukin-6 (IL-6) has been investigated frequently in stress research, knowledge regarding the biological processes of IL-6 in association with psychosocial stress remains incomplete. This study focused on salivary IL-6 and reports its temporal variation and biological correlates following acute psychosocial stress. Fifty healthy young adults (39 male and 11 female students) were subjected to the psychosocial stress test 'Trier Social Stress Test' (TSST), wherein the participants were asked to deliver a speech and perform a mental arithmetic task in front of 2 audiences. Collection of saliva samples, measurement of heart rate, and assessment of negative moods by visual analogue scales were conducted before, during, and after TSST. Salivary IL-6 levels increased by approximately 50% in response to the TSST and remained elevated for 20min after the stress tasks were completed. Cluster analyses revealed that individuals with sustained elevation of IL-6 levels following the TSST exhibited a lower cortisol response compared to individuals with lower IL-6 levels. In the correlation analyses, a greater IL-6 response was associated with a higher heart rate during the mental arithmetic task (r=.351, p<.05) and with a lower cortisol response (r=-.302, p<.05). This study demonstrates that salivary IL-6 levels are elevated for a relatively long period following acute psychosocial stress, and suggests that sympathetic activity and cortisol secretion are involved in elevation of salivary IL-6 levels.
    Biological psychology 07/2013; · 4.36 Impact Factor
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    ABSTRACT: Organisms prefer to receive rewards sooner rather than later because they excessively discount the subjective value of future rewards, a phenomenon called delay discounting. Recent studies have reported an association between cortisol-which is secreted by the hypothalamic-pituitary-adrenal (HPA) axis-and delay discounting. However, no study has examined whether acutely induced psychosocial stress modulates delay discounting. Thus, the present study examined the effect of acute psychosocial stress and its hormonal and inflammatory correlates on the rate of delay discounting. To accomplish this purpose, we assessed the participants' discounting rates using the questionnaire version with inter-temporal choice before and after an acute psychosocial stress task (the Trier Social Stress Test; TSST). The results demonstrated that TSST increased rates of delay discounting in only cortisol responders (not in non-responders), indicating the possible influence of the pathway from the HPA axis to the dopaminergic systems under acute stress. Furthermore, the findings of correlation analysis indicated a U-shaped relationship between baseline level of C-reactive protein and delay discounting rate, suggesting a complex relationship between inflammatory markers and delay discounting rate.
    Psychoneuroendocrinology 06/2013; · 5.14 Impact Factor
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    ABSTRACT: In this study, we investigated levels and relative ratios of adrenal hormones (including cortisol, dehydroepiandrosterone [DHEA], and DHEA-sulfate [DHEA-S]) and their psychophysiological correlates under acute psychosocial stress in individuals with irritable bowel syndrome (IBS). Fifty-three college students participated in the study (male: 42, female: 11; mean age: 22.64years), including 13 individuals with IBS (IBS group) and 40 individuals without IBS (control group). The participants were exposed to a standardized laboratory stressor, which included delivering a speech and performing a mental arithmetic task. We measured subjective stress levels and salivary cortisol, DHEA, and DHEA-S levels at relevant time points before, during, and after the tasks. DHEA-S level and the DHEA-S/DHEA ratio in the IBS group were significantly lower than those in the control group, and the cortisol/DHEA-S ratio in the IBS group was higher than that in the control group throughout the experiment. In the IBS group, the appraisal of a threat was positively correlated with cortisol levels (r=0.61), and the appraisal of controllability was negatively correlated with cortisol levels (r=-0.64) and with the cortisol/DHEA ratio (r=-0.71). The control group showed a significant positive correlation between the appraisal of threat and cortisol levels (r=0.32). The present study indicates that individuals with IBS had lower DHEA-S levels, and that their stressful cognitive appraisals under acute psychosocial stress caused the effects of cortisol to dominate. This adrenal hormone response may be involved in exacerbating abdominal symptoms in individuals with IBS.
    International journal of psychophysiology: official journal of the International Organization of Psychophysiology 01/2012; 84(1):39-44. · 3.05 Impact Factor