Abstract
Neuronal learning activity is reactivated during sleep but the dynamics of this reactivation in humans are still poorly understood. Here we use multivariate pattern classification to decode electrical brain activity during sleep and determine what type of images participants had viewed in a preceding learning session. We find significant patterns of learning-related processing during rapid eye movement (REM) and non-REM (NREM) sleep, which are generalizable across subjects. This processing occurs in a cyclic fashion during time windows congruous to critical periods of synaptic plasticity. Its spatial distribution over the scalp and relevant frequencies differ between NREM and REM sleep. Moreover, only the strength of reprocessing in slow-wave sleep influenced later memory performance, speaking for at least two distinct underlying mechanisms between these states. We thus show that memory reprocessing occurs in both NREM and REM sleep in humans and that it pertains to different aspects of the consolidation process.
Highlights
Neuronal learning activity is reactivated during sleep but the dynamics of this reactivation in humans are still poorly understood
Instead of looking for a single feature that can distinguish between conditions, multivariate pattern classification (MVPC) methods take into account and compare the whole temporospatial pattern of activity
If MVPC can determine from the sleep recording which type of visual stimulus a subject has learned before sleep, this implies that stimulus-specific reprocessing of the learned material occurs during sleep
Summary
Neuronal learning activity is reactivated during sleep but the dynamics of this reactivation in humans are still poorly understood. Recent advances in multivariate pattern classification (MVPC) methods have made it possible to investigate covert cognitive processes in continuous brain activity Using such methods on brain activity measured with functional magnetic resonance imaging (fMRI), Horikawa et al.[14] have recently shown that it is possible to decode the content of visual imagery occurring at sleep onset. After demonstrating the existence of such an activity, we were interested in the time course of memory reprocessing across the night and in sleep-stage-specific activity It has been discussed previously whether such reactivation occurs during NREM or REM sleep, and both have been implicated in memory reactivation and consolidation[12,13,15,16]. Activity that is present only at specific times during the night indicates that the underlying process is related to discrete periods of reprocessing rather than prolonged ongoing activity
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