THE ESSENTIAL
- It is neurogenesis in the hippocampus, the area of the brain where memory is stored, that is the key to nocturnal memorization.
- It is the new adult neurons, with higher plasticity than the old ones, that allow learning during sleep.
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Japanese researchers have come to understand how our brains work to memorize and learn during sleep. Memorization enabled by the plasticity of new neurons that are born in adults. Scientists from the International Institute for Integrative Sleep Medicine at Tsukuba University (Japan) published their results on June 4 in the journal Cell.
Neurogenesis in the hippocampus
The key to memorization during sleep is the ability of brain cells to regenerate. “In the adult brain, cells are not replaced as in the case of liver, blood or skin cells. recalls Masanori Sakaguchi, principal investigator of the study. However, there is neurogenesis in our hippocampus, region of the brain where memory is stored. Admittedly, this capacity for neuronal regeneration in adults is reduced, but it is nonetheless potentially beneficial.”
While this process is already known when we are awake, researchers have come to understand how it happens while we sleep. To do this, they subjected mice to a fear conditioning test in order to create a new memory in them. Concretely, it is a repetition of a moderate shock on the paw after hearing an auditory stimulus. Using a miniature microscope, the researchers recorded the activity of the new neurons.
Same process in humans as in mice
The results showed an activation of these neurons just after the shock but also during sleep and the next day when the researchers repeated the test. To test the memory of this experiment, the researchers inhibited young adult neurons optogenetically. This experiment showed that the mice only vaguely remembered the experience of waking, revealing that it is the new adult neurons, with higher plasticity than the old ones, that enable learning during sleep.
If these experiments are to be confirmed in humans, the researchers are convinced that the same process is at work. “Since hippocampal neurogenesis has been studied quite intensively in the human brain, I have no reason to doubt that new adult neurons are just as necessary for memory consolidation during REM sleep., says Masanori Sakaguchi. The latter considers that knowledge of this process “could facilitate the development of new treatments for memory disorders.”
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