Normalization of auditory sensory gating in schizophrenic patients after a brief period for sleep

Diminished suppression of the P50 component of the evoked potential following repeated auditory stimuli is one example of a deficit in elementary sensory processing in schizophrenia. Normal subjects suppress the P50 evoked potential to the second of two paired auditory stimuli. Although normal P50 suppression is occasionally observed in schizophrenic patients, it generally disappears with subsequent testing. The object of this experiment was to determine conditions for the reproducible normalization of P50 suppression in schizophrenic patients. After baseline recordings, 12 schizophrenic subjects were allowed to sleep for 10 minutes. The depth of sleep obtained was assessed by electroencephalography (EEG). Normalization of P50 suppression was observed for approximately 3 minutes in all subjects who entered slow wave sleep, but not in those whose EEG records remained desynchronized. Some change was even observed in subjects who had only persistent alpha waves. The amount of normalization was correlated with the deepest stage of sleep reached. Normal control subjects did not show this phenomenon but instead had a transient decrease in sensory gating after waking from sleep. The results suggest that schizophrenic patients may have a defect that causes a neuronal mechanism critical to sensory gating to fail after brief use, although its activity can be transiently restored by a short period of inactivity. A rapidly desensitized neurotransmitter receptor is one possible mechanism of such an effect.