Sensory responses from stimulation of the inferior Rolandic and Sylvian regions in man

During the course of 134 craniotomies under local anesthesia, 274 sensory responses to electrical stimulation were recorded as to cortical site, type of sensation, and the site and lateralization of peripheral referral. The region of cortex exposed was largely the sensorimotor region near the Sylvian fissure and the temporal lobe. Differences in the type of sensation were seen on either side of the central fissure. Sensation of movement and specific sensations were reported more commonly from stimulation in the precentral region and crude sensation from the postcentral area. "Pain" was reported only once and taste not at all despite the large somatic sensory representation of the tongue. About 30% of the responses were referred to the ipsilateral side or bilaterally, with a somewhat higher percentage in the pre- than in the postcentral region. In general, the expected somatotopic sequence was followed, with tongue and mouth having the largest representation. An unexpected number of referrals to the head/face were found in the suprasylvian region, and it was uncertain whether this was part of Somatosensory area II. Eleven cases with sensory referrals to trunk/limbs in the suprasylvian area were found predominantly in the precentral region. No somatotopic pattern could be seen in these or on review of Penfield's material. Possible anatomical pathways for transmission of these responses were reviewed and questions raised as to the mechanisms involved.