Prefrontal gamma-band activity distinguishes between sound durations

The present study used magnetoencephalography to assess the cortical representation of brief sound durations during a short-term memory task. Twelve subjects were instructed to memorize sounds S1 with durations of either 100 or 200 ms during an 800-ms delay phase. Subsequently, they had to judge whether the duration of a probe sound S2 matched the memorized stimulus. Statistical probability mapping of oscillatory signals revealed several components of gamma-band activity (GBA) over prefrontal cortex. A first component with a center frequency of 40 Hz responded more strongly to longer than shorter sounds during the encoding of S1. During the subsequent delay phase, shorter and longer durations were associated with topographically and spectrally distinct GBA enhancements at 71 and 80 Hz, respectively. S2 was again associated with stronger oscillatory activation for longer than shorter sounds at approximately 72 Hz. Non matching compared with matching S1-S2 pairs elicited an additional approximately 66 Hz GBA component peaking at approximately 200 ms after the offset of S2. The analysis of magnetoencephalographic GBA thus served to identify prefrontal network components underlying the representation of different sound durations during the various phases of a delayed matching-to-sample task.