Sleep is a natural, recurring state of rest and unconsciousness in which the body
and mind undergo a series of physiological and neurological changes. It is divided
in 4 stages: REM, N1, N2 and N3, also called deep sleep, which is the lowest
level of consciousness that a person undergoes without considering it an abnormal
clinical stage. Traditionally, brain activity during sleep has been studied through
electroencephalographic recordings. In this work we propose a framework to study
N3 using ...
Sleep is a natural, recurring state of rest and unconsciousness in which the body
and mind undergo a series of physiological and neurological changes. It is divided
in 4 stages: REM, N1, N2 and N3, also called deep sleep, which is the lowest
level of consciousness that a person undergoes without considering it an abnormal
clinical stage. Traditionally, brain activity during sleep has been studied through
electroencephalographic recordings. In this work we propose a framework to study
N3 using fMRI data only. This work also had the objective of finding a new method
to classify different levels of consciousness, given that the actual methods of disorders
of consciousness diagnosis usually depend on biased interpretations of the observed
reaction of the patient to certain stimuli. The Generative Connectivity of the Arrow
of Time (GCAT), a thermodynamics inspired framework, has been used to obtain
the generative effective connectivity (GEC) of the brain, which is a measure that
includes structural and functional information. In the GCAT framework a wholebrain model is used to determine the causal mechanisms underlying changes in brain
hierarchy. Using the GEC, it has been able to classify between wake and deep sleep
in human subjects, with an accuracy of over 90%. Furthermore, relevant topological
changes have been found between these two states, identifying the brain regions
which could be responsible for the loss of consciousness in deep sleep. These results
open the door towards expanding the knowledge about sleep stages as well as being
the first steps towards achieving a systematic and objective method for disorders of
consciousness’ diagnosis.
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