Spectral entropy of cerebral fluids during human sleep measured by wearable fNIRS device

Obtaining parameters that characterize cerebral fluid interactions in the human brain is of high interest particularly as regards studies of the brain clearance and in relation to neurodegeneration diseases (NDD). Furthermore, disturbances in sleep affecting brain clearance have been linked to NDDs like Alzheimer's disease (AD). At present, polysomnography (PSG) is the methodological gold standard in sleep research being used in sleep labs. However, it does not provide direct information on cerebral fluid dynamics which may be an important parameter linked to brain clearance activity during sleep. We have developed functional near-infrared spectroscopy (fNIRS) based method for assessment of human cerebral fluid dynamics during sleep. It is optimized as a wearable sleep monitoring device enabling overnight sleep recordings at home without disturbing natural sleep. In this paper, we study spectral entropy (SE) of cerebral fluid dynamics during sleep study. Developed fNIRS technique measures, in addition to cerebral hemodynamics, cortical water concentration changes reflecting dynamics of the cerebrospinal fluid (CSF) volume in macroscale. Our preliminary results of overnight fNIRS sleep measurements from 10 adult subjects show that SE values fluctuate in cycle during the whole night sleep. It may indicate the transition among sleep stages.