PERI-THRESHOLD ENCODING OF STIMULUS FREQUENCY AND INTENSITY IN THE M100 LATENCY

RECENT work has suggested that, in addition to spatial tonotopy, pitch and timbre information may be encoded in the temporal activity of the auditory cortex. Specifically, the post-stimulus latency of the maxim al cortical evoked neuromagnetic field (M100 or N1m) is a function of stimulus frequency. We investigated the additional effect of varying t he stimulus intensity on the M100 response. A 37-channel biomagnetomet er recorded neuromagnetic fields over the temporal lobe of healthy vol unteers in response to monaurally presented tones. The frequency depen dence of the M100 latency remained remarkably invariant even at low st imulus intensity. Thus, for peri-threshold stimuli, frequency informat ion appears encoded in the temporal form of the evoked response.