Breakthrough discovery unveils how sleep affects learning and memory

The brain can memorise any sound – even meaningless sounds. Hence, a snippet of white noise, like that produced by a radio when it can’t pick up a station, can be learned if heard only a few times; the listener doesn’t even have to be paying attention.

MICCN Dr Thomas Andrillon has been part of an innovative study led by the Laboratoire de Sciences Cognitives et Psycholinguistique (CNRS / ENS / EHESS) in collaboration with the Laboratoire des Systèmes Perceptifs (CNRS / ENS) and the Centre du Sommeil et de la Vigilance (AP-HP / Paris Descartes University) at Hôtel Dieu Hospital. The investigators used the kind of passive auditory stimulation you experience when white noise is played to explore the connection between learning and sleep.

Sleeping participants were exposed to noise that incorporated repeated sounds while their brain activity was tracked using electroencephalography. Since the brain reacts differently to new, unfamiliar sounds as opposed to learned sounds, electroencephalographic analysis showed the researchers whether a sound heard had been memorised, even when the subject was not awake.

The results demonstrated that the brain is capable of learning such sound patterns during both REM sleep and stage N2 sleep, revealing our surprising ability to memorise new representations while dozing. Furthermore, the researchers found that during deep sleep (stage N3), sounds previously learned during N2 sleep are forgotten, or unlearned, as if erased from memory, and that after waking, subjects found these sounds even harder to learn than completely new ones.

“These findings support the idea that N2 and REM sleep favour cerebral plasticity and active memory consolidation, while N3 sleep seems to fulfil the necessary function of unloading memories that would otherwise accumulate day after day,” says Dr Andrillon. “These novel results are important because they could reconcile two theories on sleep’s function in memory that are often deemed contradictory: one sees sleep as a time for consolidating knowledge acquired during the day; the other imagines it to be a sieve for discarding information no longer needed.”

The team now plans to explore what precise neural mechanisms underlie the double role sleep plays in memory, to understand how the brain can promote learning or forgetting. Such mechanisms could be used to improve the consolidation of specific memories during sleep or even to create new ones. It could also serve to facilitate forgetting, particularly in the case of traumatic memories.

Dr Thomas Andrillon was recently presented with the 2018 Sleep Research Society Outstanding Early-Career Investigator Award for this research. The award recognises an outstanding research effort by an early-stage investigator in the field of sleep research.

The full paper, “Formation and suppression of acoustic memories during human sleep”, was published in Nature Communications in August 2017.

For more information on his research, please contact Dr Thomas Andrillon on t: 0457 961 786, e: Thomas.Andrillon@monash.edu.

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