Sleep Disorders and Psychiatry

Jung Ki Kim is a cognitive Neuropsychologist with specialty on memory and sleep. She has conducted research on the role of sleep in consolidation and recall of memory. Recently she has been mostly interested in the relationship between sleep and happiness. She received a PhD in Experimental Psychology (on memory and amnesia) from State University of New York at Stony Brook, USA. She is Professor of Psychology and Director of Counseling Center at Pohang University of Science & Technology, Korea.

Although social relationships are essential for happiness, people spend about 1/3 of their life alone, sleeping. While insomnia is a major symptom of depression, depression is also known to be caused by long-term insomnia. In this study, the effects of sleep quality on life satisfaction and peer intimacy are examined. Further, we investigated its underlying psychological mechanism. Based on previous findings on the role of sleep in recall of emotional memories, it was hypothesized that a good sleep would promote life satisfaction as well as peer intimacy by increasing the likelihood of recalling everyday social episodes in a positively biased manner. 101 college students (study 1) and 202 high school students (study 2) in Korea completed a survey twice with a two-week interval. At time 1, baseline level of happiness (study 1) and peer intimacy (study 2); and at time 2, sleep quality, current life satisfaction (study 1) and peer intimacy (study 2) were assessed. In both times, participants were asked to recall the same three social episodes of the day. The degrees of reported positivity of each episode were averaged to form a single positivity score. The mediation analysis was used to examine the indirect effect of sleep quality on life satisfaction as well as peer intimacy via the positivity of recalled experiences. Results (study 1) revealed that, controlling baseline variables, last night’s good sleep portends today’s life satisfaction. Moreover, this relationship was partially mediated by the degree of positivity in the retrieved episodes (b=.28, SE=.29, p<.01, CI95=[0.02, 0.16]). Study 2 also revealed that, sleep quality predicted increased peer intimacy via the positivity in the retrieved episodes (b=.02, SE=.01, p<.05, CI95=[0.01, 0.05]). The present findings showed a clear positive feedback loop between sleep quality and happiness. We opened interesting questions on a relatively unexamined, nonsocial component of happiness, sleep. We emphasized the societal implications of a good sleep: improving the public awareness on the importance of sleep can contribute to the increased national health and well-being.