The resting EEG in endogenous depressions, characterized by an increase of slow alpha- and subalphacomponents and a change of spatial organization of background activity, indicates a lowered level of vigilance, If the physiological diurnal increase of the dominant alpha-frequency compensates the described slowing of alpha-rhythm, the typical daily mood fluctuation of endogenous depressions will result. 2. Changes in the resting activity occurring during arousal are probably related to the functional alteration of the EEG-sleep activity, especially to the diminishing of phasic REM-activity. 3. It is suggested that the alterations in EEG pattern during sleep and wakeful state, indicating a dissolution of slow sleep activity and a deficiency of the arousal functions, represent a regression towards an immature functioning of the vigilance regulation.
