D'un point de vue évolutif, c'est tout de même étrange. En effet, dans un environnement hostile, nos ancêtres se retrouvaient à être très vulnérables pendant de longues heures. C'est encore vrai pour de nombreuses espèces d'animaux sauvages.
Alors pourquoi le sommeil est-il tout de même universellement nécessaire?
Une nouvelle réponse intéressante commence à émerger: on dort pour oublier!
Extraits de la nouvelle:
A pair of papers published on Thursday in the journal Science offer evidence for another notion: We sleep to forget some of the things we learn each day.
In order to learn, we have to grow connections, or synapses, between the neurons in our brains. These connections enable neurons to send signals to one another quickly and efficiently. We store new memories in these networks.
In 2003, Giulio Tononi and Chiara Cirelli, biologists at the University of Wisconsin-Madison, proposed that synapses grew so exuberantly during the day that our brain circuits got “noisy.” When we sleep, the scientists argued, our brains pare back the connections to lift the signal over the noise.
In the years since, Dr. Tononi and Dr. Cirelli, along with other researchers, have found a great deal of indirect evidence to support the so-called synaptic homeostasis hypothesis.
It turns out, for example, that neurons can prune their synapses — at least in a dish. In laboratory experiments on clumps of neurons, scientists can give them a drug that spurs them to grow extra synapses. Afterward, the neurons pare back some of the growth.
Other evidence comes from the electric waves released by the brain. During deep sleep, the waves slow down. Dr. Tononi and Dr. Cirelli have argued that shrinking synapses produce this change.