Reactivity cycle of somatosensory cortex in humans with and without psychiatric disorder.

With a photographic averager to extract evoked cortical responses, reactivity cycles of primary potentials were determined over 200 milliseconds in 105 subjects. The typical cycle was biphasic, with peaks before 20 and after 100 msec. Subjects who were not psychiatric patients showed full recovery of responsiveness during the initial peak phase, whereas most of the psychiatric patients did not.