PT703. Sleep under exposure to dim light of 10 lux for one night could decline one’s brain activation during working memory task: one evidence from fMRI study

This study was conducted to investigate the effect of the exposure to dim light during sleep on the brain activation while conducting tasks requiring working memory. 23 young healthy subjects participated in this study. The subjects were instructed to sleep in a polysomnography room with no light exposure on the first night and under a dim light condition of 5 lux or 10 lux on the second night. After each of the first and the second night, the participants underwent the functional magnetic resonance imaging (fMRI) while performing the n-back test. Statistical parametric maps of brain regions showed more activation in the right inferior frontal gyrus (p FWE-corrected = 0.014) before exposure, compared to the post exposure to 10 lux light during the n-back task, although the change of the response accuracy after the light exposure was not significant in the n-back task. The decreases of fMRI activity in right inferior frontal gyrus (p FWE-corr = 0.033) and left frontal gyrus (p FWE-corr = 0.010) areas were more significant during the 2 back task rather than 1 or 0 back task in the group exposed to the light of 10 lux. To our knowledge, this is the first report on the decline of brain activation using the fMRI during N back task after sleep with an exposure to dim light. The dim light exposure might influence the brain function related to cognition although we could not feel the significant impairment in the subjective symptoms.