• The researchers managed to decode the brain activity during sleep of participants by combining artificial intelligence, MRI and EEG.
  • They found that certain areas of the brain activate and communicate with each other during sleep, which strengthens the bond between neurons.
  • They also found that our brains selected more “good” memories, and that these were therefore more easily consolidated.

What does our brain do during the long hours we are asleep? It draws our dreams… But also consolidates our memory, reveals a new study conducted by scientists from the University of Geneva (UNIGE) and published in Nature Communications, which opens for the first time a window on the sleeping human mind.

A combination of artificial intelligence, MRI and EEG

The researchers explain that they have developed an artificial intelligence capable of decoding brain activity during sleep. By combining functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), it shows that, during our deep sleep, our brain does a job of sorting through the thousands of information processed during the day. During deep sleep, our brain no longer receives external stimuli and can evaluate all these memories to retain only the most useful. To do this, it establishes an internal dialogue between its different regions, notably the hippocampus (the region of the brain that stores temporary traces of recent events) and the cerebral cortex.

It is to better understand this process that researchers have developed a decoder “able to decipher the activity of the brain in deep sleep and what it corresponds to, says Virginie Sterpenich, a researcher and co-author of the study. In particular, we wanted to see to what extent positive emotions play a role in this process “.

To complete their experiment, the scientists placed volunteers in an MRI in the early evening and had them play two video games: a face recognition game similar to “Who is this?” and a 3D labyrinth from which you have to find an exit. These games were rigged without the knowledge of the volunteers so that only one of the two games could be won for the brain to associate the game won with a positive emotion.

The volunteers then slept in the MRI for an hour or two – the length of a sleep cycle – and their brain activity was re-recorded. “We combined the EEG, which measures sleep states, and the functional MRI, which takes a picture of brain activity every two seconds, then we used a neural decoder to determine if the observed brain activity during the play period spontaneously reappeared during sleep “, explains Sophie Schwartz, who led the work.

Rewards memorized during sleep

By comparing MRI scans of the waking and sleeping phases, the scientists observed that during deep sleep, the brain’s activation patterns were very similar to those recorded during the play phase. “And, very clearly, the brain relived the game won and not the game lost by reactivating the regions used during the day before. As soon as we fall asleep, the brain activity changes. Gradually, our volunteers started to think again. ‘to both parties, then almost exclusively to the game they won when they went into deep sleep “, explains Virginia Sterpenich.

Two days later, the volunteers performed a memory test on both games. Again, the more gaming-related brain regions were activated during sleep, the better the memory performance. Thus, the memory associated with the reward is higher when it is spontaneously reactivated during sleep. With this work, the Geneva team is opening up a new perspective in the study of the sleeping brain and the incredible work it does every night.