Cerebral Responsiveness in Psychiatric Patients

Measurement of the electrical potentials evoked at the cortex in response to sensory stimulation offers a direct means of studying some aspects of cerebral responsiveness in man. Although not visible in the usual human electroencephalogram (EEG), these potentials may be recorded from the scalp by averaging procedures.2We have previously reported the results of studies in which the recovery, or reactivity, cycle of somatosensory responses was compared in normal and psychiatric populations.11,12The recovery cycle is determined by administering pairs of stimuli, separated by varying intervals. The relative size of the second, compared to the first, response of a pair indicates the extent to which the system has recovered its capacity to respond after a given interval. In nonpatient control subjects, there was usually an initial phase of full recovery, which occurred within 20 milliseconds. The main difference between controls and psychiatric patients was