Summary
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:
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1.
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.
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2.
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.
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3.
Low threshold spots for a given movement were distributed along the direction of radial fibers within the gray matter constituting a columnar shape.
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4.
Within a given columnar efferent zone, the thresholds were lower in the deep layer (V) than in the superficial layers.
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5.
Each efferent zone had a sharp boundary, and frequently overlapped with another efferent zone which produced an opposite movement.
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6.
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.
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7.
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.
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Asanuma, H., Rosén, I. Topographical organization of cortical efferent zones projecting to distal forelimb muscles in the monkey. Exp Brain Res 14, 243–256 (1972). https://doi.org/10.1007/BF00816161
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DOI: https://doi.org/10.1007/BF00816161