THE P50 EVOKED-POTENTIAL COMPONENT AND MISMATCH DETECTION IN NORMAL VOLUNTEERS - IMPLICATIONS FOR THE STUDY OF SENSORY GATING

Sensory gating is a complex, multistage, multifaceted physiological fu nction believed to be protecting higher cortical centers from being fl ooded with incoming irrelevant sensory stimuli. Failure of such mechan isms is hypothesized as one of the mechanisms underlying the developme nt of psychotic states. Attenuation of the amplitude of the P50 evoked potential component with stimulus repetition is widely used to study sensory gating. In the current study, we investigated the responsivene ss of the P50 component to changes in the physical characteristics of ongoing trains of auditory stimuli. Forty normal volunteers were studi ed in a modified oddball paradigm. At all cerebral locations studied, P50 amplitudes were higher in response to infrequent stimuli. We postu late that the increase in P50 amplitude reflects the system's recognit ion of novel stimuli or ''gating in'' of sensory input. The ratio of t he amplitude of the responses to the infrequent stimuli to those of th e frequent stimuli was significantly higher for the posterior temporal regions. This finding provides further evidence that the temporal lob es may be significantly involved in sensory gating processes. Although this study only included normal subjects, the data generated contribu te to the understanding of sensory gating mechanisms that may be relev ant to psychotic states.