Effects of Duration and Number of Onset/offsets in a Sound on Auditory Evoked Brain Magnetic Fields
Seiji Nakagawa, Toshiaki Imada, and Shoogo Ueno

The effects of stimulus duration and numbers of onset/offsets in a stimulus on auditory-evoked brain magnetic fields (N1m) were examined. Trains of 0.2-ms clicks were used as auditory stimuli by changing the number of clicks and the click interval. Auditory brain magnetic fields evoked by the click-trains were recorded in 10 normal-hearing adult subjects with a whole-head neuromagnetometer. Equivalent current dipoles were estimated in both hemispheres at N1m peak latencies. Moments of equivalent current dipoles, i.e. N1m magnitudes, significantly increased with the stimulus duration, and leveled when the stimulus duration reached 32 ms. N1m latencies significantly decreased as the stimulus duration increased, and leveled at 16 ms. N1m magnitudes produced by the trains with the same number of clicks were larger in magnitude for 4-ms-interval than that for 1- and 8-ms-interval trains, and shorter in latency for 1-ms-interval than that for 4- and 8-ms-interval trains. These results indicate that all clicks received within 16-32 ms are integrated, and that this integration is affected by the click interval.

Key words: stimulus duration, magnetoencephalography, auditory cortex