It is a dense and agitated circulation of information between the neurons which occupies the brain during the phases of sleep to consolidate the memory. Explanations on this neuronal agitation described for the first time by an INSERM team.
We know the essential role of sleep in the consolidation of memory. During its different phases, it notably allows the brain to sort out important or useless information. On the other hand, it was not known what method the neurons use to carry out this work. The work of an INSERM team which has just been published in ScienceAdvance allow us to see more clearly in this process which turns out to be much more complex than we imagined.
Brain cells are constantly exchanging information and, during sleep phases, this activity is used in particular to consolidate memory. The electroencephalogram, which makes it possible to measure the overall activity of the brain, shows regular waves, more or less rapid, according to the phases of sleep, but does not make it possible to know how each piece of information is processed at the level of the neuron.
The information journey is constantly changing
“We imagined that neurons functioned according to a very specific and repetitive pattern to transmit information or store it,” explains Christophe Bernard of the Institute of Systems Neuroscience at INSERM. By using electrodes recording the electrical activity of a hundred neurons concentrated in a given region of the brain, his team found that the path of information is in fact constantly changing: groups of neurons organize themselves for very short times to store and transmit information by constantly relaying each other, only a few of these neurons playing a major role within each group.
“There is thus a succession of sub-states with, in the end, approximately half of the neurons of the three regions which are the hippocampus, the prefrontal cortex and the entorhinal cortex which play a key role in the processing of information at one moment or another. In other words, there is no hierarchy established within the neurons but rather a balanced distribution of roles”, emphasizes Christophe Bernard.
“It’s a bit like on the internet”
And it is in the discovery of this complex process that the researchers’ surprise lies: “The dominant theory was that the transfer of information followed a fixed path, a bit like a well-regulated industrial machine, or this is not the case!”, recognizes Christophe Bernard.
And he chooses, to illustrate how information does not always follow the same path, an image that refers to the functioning of digital means of communication: “It happens a bit like on the internet, an email that goes from Paris to Sydney will go through servers in different countries as it travels, and those servers will vary throughout the day depending on traffic; in the brain it’s the same, even when the information is the same, the routes it takes don’t are not fixed and the partners change all the time!”.
Better understand the language of neurons
This work has also made it possible to better understand the “language” of neurons: a sub-state corresponds to a word, a sequence of sub-states constitutes a sentence, i.e. this language is complex, as for languages human beings, this complexity being greater during paradoxical sleep (the one during which dreams are expressed) than during slow-wave sleep. This offers a line of research to study in particular the possible link between memory loss in epileptic subjects and the complexity of neural language.
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