It is clear that cortical control of movement is not vested exclusively in the classic "motor area" of the precentral gyrus. Extrapyramidal corticifugal fibers originate from parietal, temporal, and occipital loci, as well as from all major parts of the frontal lobes.* Electrical stimulation of these regions may evoke adversive or synergic movements of the eyes, ears, head, trunk, and limbs.† Moreover, the pyramidal tract arises from a more extensive cortical region than was previously supposed. Lassek9 has reported that ablation of Area 4 causes degeneration of only 27% to 40% of pyramidal fibers. Chromatolysis in the parietal lobe following spinal hemisection10 indicates parietal components, which have received further confirmation in experiments employing antidromic stimulation of the pyramid.11 Finally, degenerated fibers have been found in the pyramidal tract following parietal,12 temporal, and occipital ablations.13
The functional significance of the dichotomy between pyramidal and extrapyramidal projections,
SEMMES J, CHOW KL. Motor Effects of Lesions of Precentral Gyrus and of Lesions Sparing This Area in Monkey. AMA Arch NeurPsych. 1955;73(5):546–556. doi:https://doi.org/10.1001/archneurpsyc.1955.02330110062009
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