Sleep-stage and event dependency of brain asynchrony as manifested through surface EEG

Electroencephalography (EEG) is a core measurement in overnight sleep studies. In this paper we study functional asymmetries of the brain as manifested through spectral correlation coefficient. Our target group is patients symptomatic of sleep apnea and referred for routine Polysomnography (PSG) testing at the hospital. We measured EEG data (using electrodes C4/A1 and C3/A2 of the International 10/20 System) as a part of the routine PSG test. Spectral correlation coefficients were computed between EEG data from the two hemispheres, for each frequency band of interest: delta, thetas, alpha , and beta. Our results indicated that hemispheric correlation distinctly changes with the gross sleep type (REM/NREM) as well as with different sleep stages (stages 1-4) within NREM. It also varies in the presence of arousal events and apnea. These results may provide a basis for novel insights into the functional asymmetries of brain in sleep and sleep associated events such as arousals and apnea