Event-related EEG field changes in aroused subjects and schizophrenic patients

The average auditory event-related potential (AAEP) to nonmeaningful stimuli has maximum vertex negative and positive amplitudes at about 100 and 200 msec, respectively. This "vertex potential" was studied under different arousal conditions in 15 normal men and 30 chronic schizophrenic subjects using the average event-related vector electro-encephalogram (AEVE) and the AAEP. The AEVE shows the path, in time, of the event-related electric field vector. To produce intramodal arousal, normal subjects also had EEG recordings made during the random sounding of a loud bell. AAEPs and AEVEs were calculated for spontaneous changes in arousal, as indicated by EEG delta band power. Bell arousal of the normal subjects increased the AAEP and AEVE measures of vertex potential maxima, thus increasing the existing differences between normals and schizophrenics. Analysis of the AEVE path indicates that arousal increased the electric field intensity, but probably did not alter, within the first 250 msec, the spatial distribution of the cortical EEG generators. After 250 msec, a reorganization of generators was indicated for the three groups. Schizophrenics differed from normals in the decreased maximum intensity of the vertex negative electric field, which was indicated by both the AEVE and AAEP.