The complexities of memory suppression

Nocturnal activities

Hippocampal-regionIn February 2011, a study carried out at the CRC (published in The Journal of Neuroscience(2)) focused on the possible role of sleep in sorting out important information (to be remembered) and information that isn’t really relevant (to be forgotten). The experimental protocol used by the researchers prefigured the one that was used for the work published later in Plos One: volunteers were shown words, some of which had to be remembered and others that had to be forgotten. After having been confronted with all the items, half of the participants were able to sleep the following night while the other half was deprived of sleep. Three days after the learning phase, the subjects were invited to take part in a memory test relating to all the words presented; these words were placed among the same number of control words. Why wait three days? So that tiredness wouldn’t influence the performance and brain activations of the participants who had stayed awake the night after the learning phase.

The participants' brain activity was recorded by fMRI, especially during the encoding phase. In the subjects who had slept, and only these subjects, it appeared that the activity of the hippocampus was predictive of the future of the information. While the hippocampus was more active during the encoding of the words to be remembered than during that of the words to be forgotten, it also revealed, within the group of "sleepers" only, a more intense activity regarding the words to be remembered, which had indeed been retained, than among those that had been unintentionally forgotten. This relation wasn’t observed in subjects who had been deprived of sleep after the learning phase; therefore, we can consider that the hippocampus consolidates certain pieces of information during sleep, especially those which are important to the subject. Here, sleep would appear to be paramount in the selection and long-term memorisation of such information.

(2) G. Rauchs, D. Feyers, B. Landeau, C. Bastin, A. Luxen, P. Maquet, F. Collette, Sleep Contributes to the Strengthening of Some Memories Over Others, Depending on Hippocampal Activity at Learning, dans The Journal of Neuroscience, 31(7), 2563-2568, 2011.

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