Background: In this study, we examined the relationships between reward-based decision-making in terms of learning rate, memory rate, exploration rate, and depression-related subjective emotional experience, in terms of interoception and feelings, to understand how reward-based decision-making is impaired in depression. Methods: In all, 52 university students were randomly assigned to an experimental group and a control group. To manipulate interoception, the participants in the experimental group were instructed to tune their internal somatic sense to the skin-conductance-response waveform presented on a display. The participants in the control group were only instructed to stay relaxed. Before and after the manipulation, the participants completed a probabilistic reversal-learning task to assess reward-based decision-making using reinforcement learning modeling. Similarly, participants completed a probe-detection task, a heartbeat-detection task, and self-rated scales. Results: The experimental manipulation of interoception was not successful. In the baseline testing, reinforcement learning modeling indicated a marginally-significant correlation between the exploration rate and depressive symptoms. However, the exploration rate was significantly associated with lower interoceptive attention and higher depressive feeling. Conclusions: The findings suggest that situational characteristics may be closely involved in reward exploration and highlight the clinically-meaningful possibility that intervention for affective processes may impact reward-based decision-making in those with depression.

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Purpose Bedtime procrastination (BP) is a prevalent and problematic phenomenon in the general population. However, no study on BP has been conducted in Japan, where people sleep the least in the world. The current study developed the Japanese version of the Bedtime Procrastination Scale (BPS) and investigated the relationship between BP, demographic features, and sleep outcomes in a population with a wide range of demographics. Methods To investigate BP in Japan, we developed the Japanese version of the BPS and assessed its internal consistency, test-retest reliability, factor structure validity, construct validity, and criterion-related validity in two samples (N= 252 and N=630). We also investigated the relationship between BP and demographic features (gender, age, and employment status) and sleep outcomes (Athens Insomnia Scale, sleep hours, sleep onset latency, and sleep efficiency).Results: The BPS showed good internal consistency, test-retest reliability, and factor structure, construct, and criterion-related validity. Moreover, BPS scores were moderately higher for younger participants than for those in their 40s and older, slightly higher for females than for males, and non-significantly different between the employment statuses. Conclusions This study provides new data on demographic predictors of BP in the Japanese population, which is characterized by short sleep duration. Although there were no clear effects of gender and employment status on BP, age was a relatively strong predictor of BP in the Japanese population. Particularly, individuals in the younger age groups had a higher BP risk than those in the older age groups. This finding warrants further studies targeted at young individuals.

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