Independent domains of inhibitory gating in schizophrenia and the effect of stimulus interval.

OBJECTIVE: Patients with schizophrenia are known to have inhibitory gating deficits in the suppression of evoked potential P50 response to repeated stimuli and the prepulse inhibition of the startle response. In the current study, the authors aimed to determine whether these two inhibitory gating measures are related in schizophrenia patients or whether abnormal P50 suppression and abnormal prepulse inhibition are independent neurophysiological characteristics of schizophrenia. The authors hypothesized that the relationship of the two measures may vary as a function of interstimulus intervals of stimulus presentations.
METHOD: Fifty-nine schizophrenia patients and 17 healthy comparison subjects were tested on both P50 suppression and prepulse inhibition. P50 suppression was measured using paired clicks with 500-msec interstimulus intervals. Prepulse inhibition was measured by using a series of prepulse-pulse pairs with interstimulus intervals ranging from 30 to 500 msec.
RESULTS: Patients showed reduced P50 suppression and prepulse inhibition in relation to healthy comparison subjects. Concordance analysis showed that abnormal P50 suppression and abnormal prepulse inhibition do not necessarily occur together. Prepulse inhibition was most prominent at the 120-msec interstimulus interval, which was not correlated to P50 suppression. At the 500-msec interstimulus interval, prepulse inhibition was significantly but negatively correlated to P50 suppression. Prepulse inhibition at the other interstimulus intervals was not correlated with P50 suppression.
CONCLUSIONS: These neurophysiological measures lack robust and direct relationships and likely mark independent aspects of abnormal brain inhibitory functions in schizophrenia.