Topographical organization of cortical efferent zones projecting to distal forelimb muscles in the monkey
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The functional organization of a cortical efferent system controlling contralateral distal forelimb muscles was examined in monkeys using the method of intracortical microstimulation (ICMS). The results obtained are:
Thresholds of stimulation for producing contraction of contralateral distal forelimb muscles were much lower (less than 1/100) in the depth of the cortex than on the surface.
These low threshold spots were confined to a small region of the cortex (hand area) and ICMS with the same strength in the neighboring cortex did not produce contraction from any part of the body.
Low threshold spots for a given movement were distributed along the direction of radial fibers within the gray matter constituting a columnar shape.
Within a given columnar efferent zone, the thresholds were lower in the deep layer (V) than in the superficial layers.
Each efferent zone had a sharp boundary, and frequently overlapped with another efferent zone which produced an opposite movement.
Efferent zones controlling various movements of a joint were located close together and zones projecting to proximal muscles were located more rostrally than those projecting to distal muscles.
These efferent zones constitute a fine mosaic organization within the depth of the cortex and functional significance of the organization was discussed in relation to the pyramidal tract.
Key wordsMotor cortex Monkey Microstimulation
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