Abstract
The conditioning-testing (S1-S2) P50 auditory evoked potential (EP) has been well-documented and accepted as an important tool for measuring sensory gating in schizophrenia research. However, the physiological mechanism of the phenomenon is not known. In this study a single-trial analysis was used to determine the influence of the latency variability of the responses in the formation of the averaged P50. Ten schizophrenic patients and 10 normal controls were tested in the dual-click EP paradigm. Using ensemble averaging analysis, we replicated the previous finding of a lower S1 P50 amplitude and higher S2/S1 ratio in schizophrenics compared with normal controls. The single-trial analysis revealed that patients had significantly higher trial-to-trial latency variability in S1 responses than normal subjects, while the showed S2 the same variability as in controls. Measured by the single-trial procedure, the arithmetic mean amplitudes of P50 responses to S1 and S2 were similar between normal and schizophrenic subjects. The same measure also eliminated the difference in averaged P50 amplitude between S1 and S2 for both groups. Temporal variability appears to be an important factor in the assessment of averaged EPs and thus contribute to the change of P50 amplitude observed in schizophrenia. © 1997 Elsevier Science Ireland Ltd.
Highlights
Changes in the auditory P50 evoked potential ŽEP. in schizophrenic patients have been well accepted as one of the electrophysiological indices of sensory gating abnormalities in schizophrenia ŽAdler et al, 1982, 1985; Freedman et al, 1983, 1987; Franks et al, 1983; Siegel et al, 1984; Baker et al, 1987, 1990; Boutros et al, 1993
Matched t-tests within each group revealed that the latency of P50 to S2 was significantly more variable than the latency of P50 to S1 in normal subjects Ž P0.001. but not in schizophrenic patients Ž Ps 0.15
In addition to the increased S2rS1 ratio, the results of this study showed that the averaged P50 amplitude to S1 was significantly reduced in schizophrenics compared to controls, while P50 to S2 did not differ between the groups
Summary
Changes in the auditory P50 evoked potential ŽEP. in schizophrenic patients have been well accepted as one of the electrophysiological indices of sensory gating abnormalities in schizophrenia ŽAdler et al, 1982, 1985; Freedman et al, 1983, 1987; Franks et al, 1983; Siegel et al, 1984; Baker et al, 1987, 1990; Boutros et al, 1993. The time-locked average of the P50 amplitude to S2 is considerably attenuated relative to the S1 response. This is interpreted as evidence of auditory sensory gating, in which S1 activates an inhibitory system that reduces the amplitude of the response to S2 ŽAdler et al, 1982. Patients with schizophrenia have an increased S2rS1 ratio ŽAdler et al, 1982; Freedman et al, 1983, 1987; Nagamoto et al, 1989. This increased S2rS1 ratio is believed to be a biological marker ŽFreedman et al, 1983. This increased S2rS1 ratio is believed to be a biological marker ŽFreedman et al, 1983. of a fixed ŽWaldo and Freedman, 1986. and genetic ŽWaldo et al, 1991. trait in schizophrenia and suggested to reflect the primary sensory gating impairment of the disease process
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