無意識でも働く脳

The brain selectively tunes to unfamiliar voices during sleep

The brain continues to respond selectively to environmental stimuli during sleep. However, the functional role of such responses, and whether they reflect information processing or rather sensory inhibition is not fully understood. Here, we present 17 human sleepers (14 females) with their own name and two unfamiliar first names, spoken by either a familiar voice (FV) or an unfamiliar voice (UFV), while recording polysomnography during a full night’s sleep. We detect K-complexes, sleep spindles, and micro-arousals, and assess event-related, and frequency responses as well as inter-trial phase synchronization to the different stimuli presented during non-rapid eye movement (NREM) sleep. We show that UFVs evoke more K-complexes and micro-arousals than FVs. When both stimuli evoke a K-complex, we observe larger evoked potentials, more precise time-locking of brain responses in the delta band (1-4 Hz), and stronger activity in the high frequency (>16Hz) range, in response to UFVs relative to FVs. Crucially, these differences in brain responses disappear completely when no K-complexes are evoked by the auditory stimuli. Our findings highlight discrepancies in brain responses to auditory stimuli based on their relevance to the sleeper and propose a key role for K-complexes in the modulation of sensory processing during sleep. We argue that such content-specific, dynamic reactivity to external sensory information enables the brain to enter a ‘sentinel processing mode’ in which it engages in the important internal processes that are ongoing during sleep while still maintaining the ability to process vital external sensory information. SIGNIFICANCE STATEMENT: Previous research has shown that sensory processing continues during sleep. Here, we studied the capacity of the sleeping brain to extract and process relevant sensory information. We presented sleepers with their own names and unfamiliar names spoken by either a familiar (FV) or an unfamiliar voice (UFV). During non-rapid eye movement (NREM) sleep, UFVs elicited more K-complexes and micro-arousals than FVs. By contrasting stimuli that evoked K-complexes, we demonstrate that UFVs evoked larger, more synchronized brain responses as well as stronger power at high frequencies (>16Hz) relative to FVs. These differences in brain responses disappeared when no K-complexes were evoked. Our results suggest a pivotal role for K-complexes in the selective processing of relevant information during NREM sleep.

The brain selectively tunes to unfamiliar voices during sleep

　眠っている最中の脳の動きに注目した論文。深いノンレム睡眠中でも脳の聴覚処理システムは起きており「知らない人の声」に強く反応する、とのこと。眠ると意識が失われるものの、睡眠中の安全を監視するシステムが意識の代りに立ち上がるようです。　また東北大の川瀬教授の研究でも勉強中のながら聞きで学習効果が落ちる研究結果が示されました。やはり脳は無意識でも何かしら仕事はしている器官と考えるのがよさそうです。　とするとこういったところをうまく鍛えるのかいかに邪魔されないようにするのかどっちが得なのか、邪魔されないようにするのが良いですが考えておく必要はありそうです。

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【本学研究者情報】 〇医工学研究科/医学系研究科　教授　川瀬哲明 研究室ウェブサイト 【研究のポイント】 左耳に提示されるテスト音に選択的注意を向け

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