Finding traces of memory processing during sleep / Des traces de réactivation de la mémoire pendant le sommeil

OUTREACH ARTICLE / ARTICLE DE VULGARISATION
(see related scientific article below / voir l'article scientifique correspondant plus bas)

Science Daily
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Finding traces of memory processing during sleep

Summary
Sleep helps us to retain the information that we have learned during the day. We know from animal experiments that new memories are reactivated during sleep. The brain replays previous experience while we sleep – and this replay strengthens memories overnight. Up to now, it was hard to demonstrate such a reactivation in humans, because the activity of individual neurons cannot be observed and most memories will activate entire networks of brain regions. Scientists have now applied new statistical pattern detection methods from the field of machine learning to get around these problems

Résumé
Le sommeil aide à retenir l'information apprise pendant la journée. Nous savons, grâce à des études impliquant des animaux, que les nouveaux souvenirs sont réactivés pendant le sommeil. Le cerveau se "rejoue" les expériences passées durant le sommeil, et cette réactivation renforce l'encodage des souvenirs la nuit. Jusqu'à maintenant, il était difficile de prouver cette réactivation chez l'humain parce que l'activité neuronale ne peut être observée, et parce que la plupart des souvenirs activent de vastes réseaux de régions cérébrales. Or, des chercheurs ont maintenant réussi à appliquer une nouvelle méthode statistique de détection venant du champ du "Machine Learning" pour pallier ce problème. 


SCIENTIFIC ARTICLE / ARTICLE SCIENTIFIQUE

Decoding material-specific memory reprocessing during sleep in humans

Schönauer, M., Alizadeh, S., Jamalabadi, H., Abraham, A., Pawlizki, A., & Gais, S. (2017). Decoding material-specific memory reprocessing during sleep in humans. Nature communications8, 15404.

DOI: 10.1038/ncomms15404

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.