What does the brain think about while we sleep

We sleep on average a third of our life, But what does the brain do during these long hours? Thanks to an artificial intelligence method capable of decoding brain activity during sleep, scientists at the University of Geneva (Switzerland) have been able to glimpse what we think about when we sleep.

Combining functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), The team of researchers provides unprecedented evidence that the work of classifying the thousands of data processed during the day takes place during deep sleep.

Indeed, at that time, the brain, which no longer receives external stimuli, can evaluate all these memories to retain only the most usefuls. To do this, it establishes an internal dialogue between its different regions. In addition, associating a reward with specific information encourages the brain to memorize it over the long term. These results, published in the journal ‘Nature Communications’, for the first time open a window on the human mind during sleep.

In the absence of tools capable of translating brain activity, the content of our sleeping thoughts remains inaccessible. However, we do know that sleep plays an important role in memory consolidation and emotional management: When we sleep, our brain reactivates the memory trail built during the day and helps us regulate our emotions.

“To find out which brain regions are activated during sleep and understand how these regions allow us to consolidate our memory, we have developed a decoder capable of deciphering brain activity in deep sleep and what it corresponds to. In particular, we wanted to see to what extent positive emotions play a role in this process, ”explains Virginie Sterpenich, principal investigator of this study.

During deep sleep, the hippocampus, a structure in the temporal lobe that stores temporary traces of recent events, returns information stored during the day to the cerebral cortex. A dialogue is established which makes it possible to consolidate the memory by reproducing the events of the day and, consequently, by strengthening the link between the neurons.

THIS WAS THE STUDY

To carry out their experiment, the scientists placed volunteers on an MRI in the early afternoon and made them play two video games: a “Who’s Who” type facial recognition game and a 3D maze. find the exit.

These sets were chosen because they activate very different brain regions and are therefore easier to distinguish on MRI images. In addition, the games were rigged without the knowledge of the volunteers so that only one of the two games could be won (half of the volunteers won one and half the second), so that the brain associated the game won with a positive emotion.

The volunteers then slept on the MRI for an hour or two (the length of a sleep cycle) and their brain activity was again recorded. “We combine EEG, which measures sleep states, and functional magnetic resonance imaging, which takes a picture of brain activity every two seconds, and then we use a ‘neural decoder’ to determine if the brain activity observed during the period of play recurred spontaneously. during sleep ”, detail the authors.

EVEN WHEN SLEEPING, THE BRAIN LOVES REWARDS

By comparing the MRI scans of the waking and sleeping phases, the scientists observed that during deep sleep, the brain activation patterns were very similar to those recorded during the play phase.

“And, very clearly, the brain was reliving the part won and not the part lost, reactivating the regions used during wakefulness. As soon as you fall asleep, brain activity changes. Little by little, our volunteers started to “think” about the two games again, then almost exclusively the game they had won when they fell sound asleep, “says Sterpenich.

Two days later, the volunteers carried out a memory test: recognizing all the faces in the game, on the one hand, and finding the starting point of the labyrinth, on the other hand. Also in this case, the more the brain regions related to play were activated during sleep, the better the memory results. Thus, they showed that the memory associated with the reward is more important when it is reactivated spontaneously during sleep.

With information from Europa Press

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