Relations between slow (4 cps) EEG activity, sensorimotor speed, and psychopathology

Slow rhythmic activity (SRA) in the frequency range from 2.5 to 5.0 cps was studied in 20 subjects (Ss) in order to examine its effect upon sensorimotor reactions and its possible relationship to psychological findings. With monopolar EEG derivations, maximal power density of SRA is found in frontal regions, whereas bipolar leads reveal maximum occurrence of SRA over posterior areas. Reaction times (RT) to visual and auditory stimuli increase significantly during the occurrence of SRA; the amount of this prolongation (ca. 74 ms) is independent of stimulus modality but significantly correlates with SRA frequency: the lower the frequency, the higher the RT increment. In psychological tests, most Ss with SRA displayed disturbances of emotionality as well as 'pathological' values in the subscales hysteria, hypochondria, psychasthenia, and paranoia, but none of our Ss was diagnosed as psychotic. There is a high correlation between the SRA frequency and the extent of psychological deviations: Ss with low SRA frequency values are more likely to reveal psychological disturbances than Ss with high SRA frequency. The possible origin and physiological impact of SRA is discussed and the desirability of further neurophysiological studies is emphasized.