Topographic brain mapping of middle latency auditory evoked potentials in normal subjects.

Topographic brain mapping of auditory middle latency evoked responses (MLR) were obtained from 20 subjects (10 males and 10 females), all right-handed and with normal pure tone audiograms. Clicks with alternative polarity, with a rate of 7.7/sec. were delivered at an intensity of 75 dB HL monoaurally to both ears. Responses from 21 channels were amplified and band-pass filtered (3-150). All the surface maps were analyzed with a Bio-Logic Brain Atlas III system. MLR maps obtained show a quite small intrasubjective variability at the latencies of the principal components Na and Pa. The grand averages of MLR maps at the corresponding latencies in males and females were compared each other. All the entire temporal window has been segmented into some subepochs, showing similar spatial characteristics of the maps, like location of maxima and minima and, overall, shape.