POSSIBLE OVERLAPPING POTENTIALS OF THE AUDITORY P50 IN HUMANS - FACTOR-ANALYSIS OF MIDDLE LATENCY AUDITORY-EVOKED POTENTIALS

The auditory P50 in humans may consist of overlapping potentials. To t est this hypothesis, we manipulated the conditions of stimulus discrim ination and motor response difficulty and evaluated the data by factor analysis. Twenty right-handed males (mean age 27 years) performed the following 4 tasks: (1) a counting task, (2) an easy Co, No-Ga task, ( 3) a difficult Go; No-Go task, and (4) a choice reaction task. Middle latency auditory evoked potentials were obtained with 100 times summat ion triggered by the onset of the auditory stimulus. Four factors were extracted by factor analysis for a 0-100 ms time period. Factor 1, th e maximum factor loading at 91 ms, corresponded to N1, and factor 4, t he maximum factor loading at 23 ms, appeared to correspond to P30. The latency of the maximum factor loading in factor 2 was adjacent to tha t in factor 3, the latency of factor 2 being 12 ms earlier than that o f factor 3. Factor 2 and factor 3 latencies were approximately 55 ms w hich corresponded to the P50. Factor 3 started rising at the point tha t factor 2 reached the maximum factor loading, and the factor score de monstrated a significant group difference only when analyzed by motor response criteria. These results suggest that the P50 in humans consis ts of overlapping potentials and that a part of the potential might re late to a motor response process. (C) 1997 Elsevier Science Ireland Lt d.