The scalp topography of human somatosensory and auditory evoked potentials.

The waveform and topography of components of the scalp recorded somatosensory evoked poal (AEP) to click stimulation of the right ear, were determined for scalp electrode locations of the 10-20 system and for locations at the eye, mastoids, and posterior neck. Twenty-one SEP and twenty-two AEP components were analyzed. Differentiation of neurogenic and myogenic components was attempted on the basis of localization and variability. Some components of extracranial origin, apparently originating in frontal musculature, were small in most experienced subjects and large in most experimentally naive subjects. These and other presumptive myogenic potentials can distort adjacent neurogenic components. These data should aid in predicting SEP and AEP characteristics and in assessing myogenic distortion of neurogenic components.