Publication in the PNAS journal
During sleep our perception of our environment diminishes. Nevertheless the way in which the human brain reacts to surrounding noise over the course of sleep still remains poorly understood. In a study published this week in the Proceedings of the National Academy of Sciences (PNAS), researchers at the University of Liège have used cerebral imaging to analyse the brain’s responses to sound during sleep. They have demonstrated that the activity of our brain is very tightly controlled by the specific brain waves which our sleep is composed of. In particular waves called ‘sleep spindles’ prevent sounds being transmitted to the regions of the brain responsible for hearing. Conversely, when sounds are linked to the cerebral waves called ‘K-complex’ the activation of hearing regions is enhanced. Our perception of the environment is thus not reduced in a constant manner during sleep, but varies throughout it under the influence of particular waves produced by our brain.
In this study the science team led by Dr Thanh Dang-Vu and Professor Pierre Maquet (the University of Liège’s Cyclotron Research Centre) shows that the cerebral activity induced by sounds during the course of sleep depends closely on the brain waves which are sleep is made up of.
In using functional magnetic resonance imaging (fMRI) techniques combined with electroencephalography (EEG), the researchers have demonstrated that the cerebral regions responsible for hearing remain active during in response to sounds during sleep (see the illustration, left hand panels), apart from when these sounds occur whilst the brain is producing waves called ‘sleep spindles.’ The study in effect shows that the spindles prevent the transmission of sounds to the auditory cortex (see the illustration, right hand panels).
Conversely, sounds can lead to the production of particular brain waves called ‘K-complex’ over the course of sleep.’ The results provided by this new study shows that the production of these waves in response to sounds brings about a higher activation of the brain’s auditory regions. Whilst the spindles impede the transmission of sounds, K-complexes are reflected by a greater transmission of sounds to the brain during sleep.
The effects of sound on sleep are thus controlled by very specific brain waves. In particular the human brain finds itself isolated from the environment during sleep spindles, which allows it to carry out essential functions such as consolidating the memory of information learned whilst awake. These brain waves thus play an essential role in the quality of our sleep and its constancy in the face of the surrounding environment’s sounds.
“Interplay between spontaneous and induced brain activity during human non-rapid eye movement sleep“, PNAS, 2011, www.pnas.org, by T.T. Dang-Vu, M. Bonjean, M. Schabus, M. Boly, A. Darsaud, M. Desseilles, C. Degueldre, E. Balteau, C. Phillips, A. Luxen, T. Sejnowski and P. Maquet.
Left hand panels: the cerebral regions responsible for hearing remain active in response to sounds during NREM (non rapid eye movement) sleep.
Right hand panels: when sounds occur whilst the brain is producing waves called ‘sleep spindles,’ their transmission to the auditory cortex is affected. Only a small region of the brain stem (arrow) remains activated by sounds.
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Dr Thanh Dang-Vu, chargé de recherches FNRS, Université de Liège & Université de Montréal, actuellement en mission scientifique à Montréal, Mobile 001 514 947 4553, [email protected]
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