Light sleep and deep sleep are similar in that they are both forms of non-rem sleep, where the body does not have the intense dreams that characterize REM sleep. N1 and N2 sleep are thought of as light sleep while N3 and N4 are considered deep sleep. ![]() There is some debate on how many stages there are, with the American Academy of Sleep Medicine distinguishing 4 stages of sleep (REM, N1, N2, N3) and the European Academy of Sleep Medicine distinguishing 5 stages of sleep (REM, N1, N2, N3, N4). When we sleep, our body cycles through distinct sleep cycles, also known as sleep stages. This research was supported by the National Fund for Scientific Research (Belgium), the University of Liège and the Queen Elisabeth Medical Foundation.The science of sleep as we know it was discovered relatively recently when a laboratory at The University of Chicago hooked people’s brains up to electrodes and observed REM sleep in 1953. Finally, the activation of areas such as the brainstem, usually associated with arousal and waking, might reveal these oscillations of non-REM sleep as ‘micro-wake’ periods allowing the brain to fulfil crucial and active functions, even during the deepest stages of sleep. ![]() Moreover, by showing the activation of areas involved in the processing of memory traces such as para-hippocampal areas, the study might point to the potential functions of sleep, in particular the increasingly well-defined role of sleep in memory consolidation. On the other hand, they allow the identification of brain areas potentially involved in the generation of these oscillations, which are a hallmark of brain functioning during non-REM sleep. On the one hand, they demonstrate that non-REM sleep is a stage of brain activation organized by the slow oscillations. These results improve our understanding of non-REM sleep mechanisms. Besides, these activity increases are located in specific brain areas, including the inferior frontal gyrus, the parahippocampal gyrus, the precuneus and the posterior cingulate cortex, as well as the brainstem and cerebellum (see image, central panels). In a study published recently in the American journal Proceedings of the National Academy of Sciences, the research team led by Dr Thanh Dang-Vu and Pr Pierre Maquet shows that brain activity during these sleep stages is actually profoundly influenced by spontaneous slow rhythms (also called ‘slow oscillations’) which organize neuronal functioning during non-REM sleep.īy using functional magnetic resonance imaging (fMRI) combined with electroencephalography (EEG), researchers have evidenced that these slow oscillations are associated with brain activity increases during non-REM sleep (see image, side panels), therefore discarding the concept of brain ‘quiescence’ that prevailed for a long time in the characterization of non-REM sleep. ![]() Although not rejecting this concept, researchers from the Cyclotron Research Centre of the University of Liège in Belgium and from the Department of Neurology of Liege University Hospital demonstrate that, even during its deepest stages (also called ‘slow-wave-sleep’), non-REM sleep should not be viewed as a stage of constant and continuous brain activity decrease, but is also characterized by transient and recurrent activity increases in specific brain areas.
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