FUNCTIONAL-ANATOMY OF THE HUMAN SUPPLEMENTARY SENSORIMOTOR AREA - RESULTS OF EXTRAOPERATIVE ELECTRICAL-STIMULATION

Electrical stimulation studies have demonstrated that a ''supplementar y motor area'' (SMA) exists in humans. However, its precise functional organization has not been well defined. We reviewed the extraoperativ e electrical stimulation studies of 15 patients with intractable epile psy who were evaluated with chronically implanted interhemispheric sub dural electrodes. SMA-type positive motor responses were elicited not only from the mesial portion of the superior frontal gyrus but also fr om its dorsal convexity, and from the paracentral lobule, cingulate gy rus, and precuneus. Sensory symptoms, that could not be attributed to stimulation of the primary sensory area, were elicited from the superi or frontal and cingulate gyri in addition to the precuneus. Therefore, human SMA, as defined by electrical stimulation, is not always confin ed to the mesial portion of the superior frontal gyrus as described pr eviously. It is also not strictly ''motor'' but ''sensorimotor'' in re presentation. We propose referring to this region as the ''supplementa ry sensorimotor area'' (SSMA). We observed a somatotopic organization within the SSMA with an order of lower extremity, upper extremity, and head from posterior to anterior. Sensory representation in an individ ual was either anterior or posterior to the positive motor representat ion but never both. There was a supplementary eye field within the hea d representation. A supplementary negative motor area was noted at the anterior aspect of the SSMA. No language area was demonstrated within the SSMA. The physiologic significance of the SSMA and functional con sequences of its resection must be addressed in further studies.