脳活動から探る夢の内容

Exploring Dream Contents by Neuroimaging

夢は，睡眠中に生じる主観的体験であり，鮮やかな視覚内容を伴う。夢はその主観性ゆえに，客観的な解析が困難な対象であるとされていたが，睡眠中の急速眼球運動の発見から，脳活動をはじめとする生理指標と夢見との関係に関する知見が蓄積されてきた。本稿では，まず夢見と神経生理・行動指標との関係を調べた研究を概観し，その後，睡眠中のヒトの脳計測データから，見ている夢の内容を解読した最近の研究について紹介する。

Abstract

Dreaming is a subjective experience during sleep that is often accompanied by vivid perceptual and emotional contents. Because of its fundamentally subjective nature, the objective study of dream contents has been challenging. However, since the discovery of rapid eye movements during sleep, scientific knowledge on the relationship between dreaming and physiological measures including brain activity has accumulated. Recent advances in neuroimaging analysis methods have made it possible to uncover direct links between specific dream contents and brain activity patterns. In this review, we first give a historical overview on dream researches with a focus on the neurophysiological and behavioral signatures of dreaming. We then discuss our recent study in which visual dream contents were predicted, or decoded, from brain activity during sleep onset periods using machine learning-based pattern recognition of functional MRI data. We suggest that advanced analytical tools combined with neural and behavioral databases will reveal the relevance of spontaneous brain activity during sleep to waking experiences.