Topography of scalp recorded potentials evoked by stimulation of the digits

The amplitude of the primary positive deflection, P24, was measured in each wave form recorded from a 36-channel scalp electrode array placed over sensorimotor cortex. Electrical stimulation of contralateral little, middle, index finger, or thumb produced wave forms possessing common features, but the location of peak P24 amplitude depended upon the digit stimulated. With thumb stimulation peak P24 amplitude was located approximately two-thirds the distance from midline to sylvian fissure, while stimulation of the other digits resulted in more medially located topographic peaks. These shifts correlate with previous descriptions of body-part representation in somatosensory cortex and suggest that at least certain wave form deflections recorded from the scalp provide accurate localization of their underlying neural generators.