Lateral asymmetry of the scalp distribution of somatosensory evoked potential amplitude

Somatosensory potentials evoked by brief low-intensity electrical pulses delivered separately to the left and right index fingers were recorded from the scalp over the posterior half of the contralateral hemisphere in normal human subjects. In two experiments it was found that the scalp areas enclosed by 75 and 90% of maximum-amplitude isopotential contour lines of the early cortically generated complexes were more restricted over the left hemisphere. This asymmetrical evoked potential distribution supports the proposal by Semmes from her observations of brain-damaged patients that elementary somatosensory representation is focal in the left hemisphere and diffuse in the right.