The brain remains interconnected during non-REM sleep, according to new work from a European team of researchers. The finding has also made it possible to analyse the scientific basis of consciousness, an increasingly important field of neuroscience.
Sleep is composed of various cycles in which there are different stages: slow and fast-wave, which make up non-REM sleep and REM sleep. During the night, it is normal to experience four or five complete cycles, each lasting around ninety minutes.
Various investigations have shown that communication between different areas of the cerebral cortex is interrupted during non-REM sleep and also when a patient is under anaesthesia, due to the loss of consciousness.
Cerebral Correlations Preserved
Umberto Olcese, a researcher from the Swammerdam Institute for Life Sciences of the University of Amsterdam, said:
“It was thought that the brain disconnected during non-REM sleep and that the individual areas could no longer communicate effectively."
Olcese and the rest of the research team (which involved researchers from the European CANON project and that was led by Prof. Cyriel Pennartz, who participates in the European Flagship Human Brain Project) have discovered that not all forms of communication within the cerebral cortex are lost during non-REM sleep. Specifically, correlations are preserved between neurons located within individual regions and between some subpopulations of neurons located in different cerebral areas.
In a second investigation published in the same journal, a team of investigators from the Human Brain Project and the CANON project reviewed the current state of knowledge of consciousness from a neuroscience perspective.
Although historically this concept has been studied from a philosophical standpoint, experts have reviewed various scientific studies which reflect the importance of a proper communication between cortical areas in the process.
“Neuroscientific research on consciousness driven by new methods and theoretical advances should be increasingly robust and accepted, since notable scientific and clinical progress is now starting to be made,"
the authors pointed out.
“Rather than trying to solve all major theoretical problems first, we advocate an interleaved practical and theoretical approach. Experiments across scales, species, and models, spanning from ion channels, neurons, and microcircuits to whole-brain simulations, from unit and ensemble recordings in animals to the patient’s bedside, will be crucial for bridging the gaps between single-neuron dynamics, overall network complexity, and conscious experience. This is a daunting task and the stakes are high, but the recent progress is promising,"
U. Olcese, J. J. Bos, M. Vinck, J. V. Lankelma, L. B. van Mourik-Donga, F. Schlumm, C. M. A. Pennartz Spike-Based Functional Connectivity in Cerebral Cortex and Hippocampus: Loss of Global Connectivity Is Coupled to Preservation of Local Connectivity During Non-REM Sleep Journal of Neuroscience, 2016; 36 (29): 7676 DOI: 10.1523/JNEUROSCI.4201-15.2016
Joahn F. Storm, Mélanie Boly, Adenauer G. Casali, Marcello Massimini, Umberto Olcese, Cyriel M.A. Pennartz and Melanie Wilke Consciousness Regained: Disentangling Mechanisms, Brain Systems, and Behavioral Responses The Journal of Neuroscience, November 2017 DOI: 10.1523/JNEUROSCI.1838-17.2017
Image: The Sleeping Gypsy, Henri Rousseau, 1897