Monday, September 12, 2011

Brain Waves Control the Impact of Noise On Sleep

During sleep, our perception of the environment decreases. However the extent to which the human brain responds to surrounding noises during sleep remains unclear. In a study published this week in Proceedings of the National Academy of Sciences (PNAS), researchers from University of Liège (Belgium) used brain imaging to study responses to sounds during sleep.

They show that brain activity in the face of noise is controlled by specific brain waves during sleep. In particular, waves called sleep 'spindles' prevent the transmission of sounds to auditory brain regions. Conversely, when sounds are associated with brain waves called 'K-complexes', activation of auditory areas is larger. Our perception of the environment is therefore not continuously reduced during sleep, but rather varies throughout sleep under the influence of particular brain waves.

In this study, the research team led by Dr Thanh Dang-Vu and Prof. Pierre Maquet (Cyclotron Research Center, University of Liège) shows that brain activity induced by sounds during sleep closely depends on brain waves that constitute our sleep.

By using functional magnetic resonance imaging (fMRI) combined with electroencephalography (EEG), researchers have evidenced that auditory brain regions remain active in response to sounds during sleep [see image, left panels], except when sounds occur during brain waves called sleep 'spindles'. The study indeed shows that spindles prevent the transmission of sounds to the auditory cortex [see image, right panels].

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