Test-retest reliability of the P50 mid-latency auditory evoked response.

Attenuation in mid-latency auditory evoked responses (MLAERs) can be used to study sensory gating. If paired-click stimuli (S1 and S2) are used, lower amplitude in response to S2 vs. S1 (attenuation) is considered evidence for intact sensory gating. However, the need for reliable measurements of MLAER amplitude and attenuation is a recognized problem. Ten normal volunteers were studied six times each. An S1 amplitude test-retest reliability coefficient (r) of 0.585 was obtained when means of two recordings were used vs. reliability coefficients as high as 0.809 for means of six recordings. Averaging a higher number of runs (120 vs. 60) resulted in a reliability coefficient of 0.677/recording. Similar values were obtained for S1 and S2 latencies. Reliability coefficients for S2 attenuation (S2/S1) were not nearly as high (a value of 0.138 when means of all six recordings were used). The S1 amplitude as measured in this study (with 120 averages) appears to be a reliable psychophysiologic measurement, but the S2/S1 attenuation measure is more variable, perhaps reflecting a greater sensitivity of the S2/S1 to uncontrolled variables in this study. Further research to identify such variables is necessary.