Quiet please, we’re sleeping!

The first of these are called spindles and the second are called K complexes. These waves are at the heart of a cerebral control process of auditory stimuli during sleep. The spindles prevent the transmission of sounds to the regions of the brain responsible for hearing, while the K complex waves reinforce the activation of these regions. These are the results of a study carried out by Thien Thanh Dang-Vu and Professor Pierre Maquet at the Cyclotron Research Centre (CRC) of the University of Liège.

Sommeil2 copieWe have a tendency to present the brain as an organ that receives information from the external world, processes it and in turn sends back information, notably in the form of motor behavior. This is only a partial vision of the functioning of the brain because it is well-established today that our most noble organ has permanent spontaneous activity. This varies in time according to the state we are in: awake, non-rapid-eye-movement (NREM) sleep, rapid-eye-movement (REM) sleep or hypnotic state.

During the last few years, different research projects have been initiated in order to determine if the nature of the spontaneous activity of the brain modifies its response to external stimuli. Therefore, in 2008, in an article entitled When the brain predicts..., we reported the results of a study(1) whose first author was Doctor Mélanie Boly, a postdoctoral researcher at the FNRS. It was revealed in particular that, in a resting awake subject, the profile of the spontaneous activity of the brain three seconds before a somatosensory stimulation, or before a nociceptive (painful) stimulation, was predictive of the way these stimulations would be perceived.

In an article(2) which appeared in September 2011 in the American journal Proceedings of the National Academy of Sciences (PNAS), doctor Thien Thanh Dang-Vu, currently a post-doctoral researcher at the University of Montréal, and Professor Pierre Maquet, research director at the FNRS, took an interest in another side of the problem: the influence during NREM sleep of the spontaneous activity of the brain on the processing of sounds.

Pierre Maquet puts the problem into context. “In the light of our current knowledge, the brain must be understood as an organ possessing its own activity which is disturbed by the external stimuli. The model towards which the neurosciences are progressing is that of an organ applied to permanently constructing a representation of the world in wake mode and therefore of predictions, the external afferences having the role of correcting these predictions in order to better adapt them to reality. ” He adds that this process can be flawed when the external stimuli are poor in information content. This would explain, for example, a phenomenon such as optical illusions.

(1) M. Boly, E. Balteau, C. Schnakers, C. Degueldre, G. Moonen, A. Luxen, C. Phillips, P. Peigneux, P. Maquet et S. Laureys, Baseline brain activity fluctuations predict somatosensory perception in humans, PNAS, 14 juillet 2007.
(2) Thien Thanh Dang-Vu, Maxime Bonjean, Manuel Schabus, Mélanie Boly, Annabelle Darsaud, Martin Desseilles, Christian Degueldre, Évelyne Balteau, Christophe Phillips, André Luxen, Terrence J. Sejnowski et Pierre Maquet, Interplay between spontaneous and induced brain activity during human non-rapid eye movement sleep, PNAS, 2011.

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