The auditory P 50 component to onset and offset of sound

Abstract

Objective The auditory Event-Related Potentials (ERP) of component P 50 to sound onset and offset have been reported to be similar, but their magnetic homologue has been reported absent to sound offset. We compared the spatio-temporal distribution of cortical activity during P 50 to sound onset and offset, without confounds of spectral change. Methods ERPs were recorded in response to onsets and offsets of silent intervals of 0.5 s (gaps) appearing randomly in otherwise continuous white noise and compared to ERPs to randomly distributed click pairs with half second separation presented in silence. Subjects were awake and distracted from the stimuli by reading a complicated text. Measures of P 50 included peak latency and amplitude, as well as source current density estimates to the clicks and sound onsets and offsets. Results P 50 occurred in response to noise onsets and to clicks, while to noise offset it was absent. Latency of P 50 was similar to noise onset (56 ms) and to clicks (53 ms). Sources of P 50 to noise onsets and clicks included bilateral superior parietal areas. In contrast, noise offsets activated left inferior temporal and occipital areas at the time of P 50. Source current density was significantly higher to noise onset than offset in the vicinity of the temporo-parietal junction. Conclusions P 50 to sound offset is absent compared to the distinct P 50 to sound onset and to clicks, at different intracranial sources. P 50 to stimulus onset and to clicks appears to reflect preattentive arousal by a new sound in the scene. Sound offset does not involve a new sound and hence the absent P 50. Significance Stimulus onset activates distinct early cortical processes that are absent to offset.