Topography and possible physiological significance of EEG amplitude variability in psychosis.

The topography and possible physiological significance of EEG average amplitude and amplitude variability in time were examined in 10 chronic psychotic patients and several groups of healthy volunteers. In confirmation of previous reports, the patients showed more slow (5.2-7.6 Hz) activity, particularly in frontal areas, and less alpha rhythm variability in posterior areas, compared to matched controls, chiefly during the resting state, while eye opening, and particularly structural sensory input, made the groups more similar. The same two EEG variables showed significant correlations with ratings of psychopathology, in the expected direction. The EEG amplitude variability is increased by unstructured perception, probably as an expression of readiness or search for structures in the input, and shows persistent topographic patterns over time in individuals. It appears to reflect a functional dimension which is different from the one represented by the average amplitude and is one of several spontaneous oscillatory functions which are diminished in chronic psychosis, perhaps as consequence of prefrontal malfunction. The results suggest a diminished guiding function by the anterior cortex, and a diminished readiness for perception of exogenous structured information, in chronic psychosis.