Sh. Lim et al., FUNCTIONAL-ANATOMY OF THE HUMAN SUPPLEMENTARY SENSORIMOTOR AREA - RESULTS OF EXTRAOPERATIVE ELECTRICAL-STIMULATION, Electroencephalography and clinical neurophysiology, 91(3), 1994, pp. 179-193
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.