P50 inhibitory gating deficit is correlated with the negative symptomatology of schizophrenia

Abnormal sensory gating in schizophrenia has frequently been reported. The strength of central inhibitory pathways was measured using the P50 component of the auditory evoked potential in a conditioning-testing paradigm. The relationships between a relative decrease in P50 amplitude to repeated auditory stimuli and clinical symptoms remain controversial. Using the Positive and Negative Syndrome Scale, we studied the P50 auditory conditioning-testing paradigm in 81 schizophrenic subjects, categorized into subgroups with and without prominent negative symptoms, in comparison with 88 control subjects. We found increased ratios of testing stimuli to conditioning stimuli in both schizophrenic subgroups relative to findings in the control group. In addition, we found significantly increased mean latencies of the P50 responses to conditioning (C) and testing (T) stimuli and significantly increased T/C ratios in the subgroup with negative symptoms compared with the subgroup with non-negative symptoms.