Inter- and intrahemispheric relationships of the EEG activity during sleep in man

Using both linear and non-linear multivariate analysis associated with classical statistical tests, inter- and intrahemispheric relations of the cerebral electrical activity (EEG) during sleep were analysed by spectral power, coherence (CH) and correlation functions. Whilst a steady diffuse decrease in linear phase relations (CH) appeared during the evolution from waking to slow wave sleep, paradoxical sleep was associated with low interhemispheric CHs (mostly frontal) and high intrahemispheric CHs. Simultaneously, at a much lower degree of temporal resolution (25.6 sec periods), the correlations between EEG activities of identical frequencies but of different topographies were highly positive during sleep, whilst the correlations between activities of different frequencies at the same site on the scalp varied according to sleep states and frequencies. These findings suggest the interpretation of deep sleep in man as a state of transient partial disconnection between hemispheres.