LOCALIZATION OF FUNCTIONAL REGIONS OF HUMAN MESIAL CORTEX BY SOMATOSENSORY-EVOKED POTENTIAL RECORDING AND BY CORTICAL STIMULATION

We describe methods of localizing functional regions of the mesial wal l, based on 47 patients studied intraoperatively or following chronic implantation of subdural electrodes. Somatosensory evoked potentials w ere recorded to stimulation of posterior tibial, dorsal pudendal, medi an, and trigeminal nerves. Bipolar cortical stimulation was performed, and in 4 cases movement-related potentials were recorded. The cingula te and marginal sulci formed the inferior and posterior borders of the sensorimotor areas and the supplementary motor area (SMA). The foot s ensory area occupied the posterior paracentral lobule, while the genit alia were represented anterior to the foot sensory area, near the cing ulate sulcus, The foot motor area was anterior and superior to the sen sory areas, but there was overlap in these representations. There was a rough somatotopic organization within the SMA, with the face represe nted anterior to the hand, However, there was little evidence of the ' 'pre-SMA'' region described in monkeys, Complex movements involving mo re than one extremity were elicited by stimulation of much of the SMA. The region comprising the supplementary sensory area was not clearly identified, but may involve much of the precuneus. Movement-related po tentials did not provide additional localizing information, although i n some recordings readiness potentials were recorded from the SMA that appeared to be locally generated.