MOVEMENT REPRESENTATION IN THE DORSAL AND VENTRAL PREMOTOR AREAS OF OWL MONKEYS - A MICROSTIMULATION STUDY

We used intracortical microstimulation to investigate the lateral prem otor cortex and neighboring areas in 14 hemispheres of owl monkeys, fo cusing on the somatotopic distribution of evoked movements, thresholds for forelimb movements, and the relative representation of proximal a nd distal forelimb movements. We elicited movements from the dorsal an d ventral premotor areas (PMD, PMV), the caudal and rostral divisions of primary motor cortex (M1c, M1r), the frontal eye field (FEF), the d orsal oculomotor area (OMD; area 8b), the supplementary motor area (SM A), and somatosensory cortex (areas 3a and 3b). Area PMD was composed of architectonically distinguishable caudal and rostral subdivisions ( PMDc, PMDr). Stimulation of PMD elicited movements of the hindlimb, fo relimb, neck and upper trunk, face, and eyes. Hindlimb and forelimb mo vements were represented in the caudalmost part of PMDc. Face, neck, a nd eye movements were represented in the lateral and rostral parts of PMDc and in PMDr. Stimulation of PMV elicited forelimb and orofacial m ovements, but not hindlimb movements. Both proximal and distal forelim b movements were elicited from PMDc and PMV, although PMD stimulation elicited mainly shoulder and elbow movements, while PMV stimulation ev oked primarily wrist and digit movements. Distal movements were evoked more frequently from PMV than from Mlr or Mlc. Across cases, the medi an forelimb thresholds for PMDc and PMV were 60 and 36 mu A, respectiv ely, values that differ significantly from each other and from the val ue of 11 mu A obtained for M1r. Our observations indicate that premoto r cortex is much more responsive to electrical stimulation than common ly thought, and contains a large territory from which eye movements ca n be elicited. These results suggest that in humans, much of the elect rically excitable cortex located on the precentral gyrus, including co rtex sometimes considered part of the frontal eye field, is probably h omologous to the premotor cortex of nonhuman primates. (C) 1996 Wiley- Liss, Inc.