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Study Offers Insight Into Brain Activity During NREM Sleep

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Brain Activity During NREM Sleep

A study conducted by scientists at the Cyclotron Research Centre at the University of Liège, in Liège, Belgium, and the Institut National de la Santé et de la Recherche Médicale at the Université Pierre et Marie Curie in Paris, and the Functional Neuroimaging Unit at theMontreal Geriatrics Institute investigated NREM sleep (non-rapid eye movement). Scientists wanted to show that the brain’s activity is composed of many biological modules during this period of the sleep. Using functional clustering (assigning a set of objects into groups and determining the hierarchical organisation between them) they found that hierarchically organized large-scale neural networks were disaggregated into smaller independent modules while a person is in the NREM sleep, and this can reduce the brain’s ability to integrate information. This determines a lower level of consciousness than that found in REM sleep.

Sleeping Man

Sleeping Man

During the research, the team had to face the challenge that untill nowadays there is no clue regarding what consciousness really is.  Pierre Maquet, lead researcher at the Cyclotron Research Centre and Habib Benali at the Institut National de la Santé et de la Recherche Médicale explains: For many years, Giulio Tononi put forward the hypothesis that consciousness is related to the ability of the brain to integrate information. Our objective was simply to test this hypothesis.” Using novel tools that allowed the computation of information exchange within the brain, along with EEG and fMRI, they compared data recorded in the same individuals during wakefulness and deep NREM sleep which is associated to the most reduced level of consciousness found in normal  brain activity. Their findings could help science have a better understanding of the concept consciousness.

The results of the study revealed that the amount of information exchanged in the brain actually increases during sleep, but what differs from the awake-state are the patterns of exchange between different regions. “Essentially, there was an increased information exchange within small clusters of mainly homologous brain areas whereas communication between clusters significantly decreased during sleep, explains Maquet.

The team’s approach to studying the brain activity was functional clustering, which by its nature does not focus on the total integration in neural network analysis. This arises an important question, sais Maquet:  We don’t know what is the information exchanged within clusters, and I don’t see any technique that could currently answer this question in humans. More generally it is thought that NREM sleep is regulated by the homeostasis of synaptic strength, and perhaps by neuronal energy metabolism.