We sleep on average one third of our time. But what does the brain do during these long hours? Using an artificial intelligence approach capable of decoding brain activity during sleep, scientists at the University of Geneva (UNIGE), Switzerland, were able to glimpse what we think about when we are asleep. By combining functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), the Geneva team provides unprecedented evidence that the work of sorting out the thousands of pieces of information processed during the day takes place during deep sleep. At this time, the brain, which no longer receives external stimuli, can evaluate all of these memories in order to retain only the most useful ones. To do so, it establishes an internal dialogue between its different regions. Moreover, associating a reward with a specific information encourages the brain to memorise it in the long term. In the absence of tools capable of translating brain activity, the content of our sleeping thoughts remains inaccessible.
To conduct 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 ‘Guess Who?’ and a 3D maze from which the exit must be found. These games were chosen because they activate very different brain regions and are therefore easier to distinguish in the MRI images. In addition, the games were rigged without the volunteers’ knowledge so that only one of the two games could be won so that the brain would associate the game won with a positive emotion. The volunteers then slept in the MRI for one or two hours – the length of a sleep cycle – and their brain activity was recorded again. Researchers combined EEG, which measures sleep states, and functional MRI, which takes a picture of brain activity every two seconds, and then used a neuronal decoder to determine whether the brain activity observed during the play period reappeared spontaneously during sleep.
More information:
https://scienceblog.com/524152/what-does-the-sleeping-brain-think-about/