Journal
JOURNAL OF COMPARATIVE NEUROLOGY
Volume 524, Issue 3, Pages 448-455Publisher
WILEY
DOI: 10.1002/cne.23792
Keywords
motor control; motor cortex; motor neurons; cortical expansion; number of neurons
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Funding
- Filho de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ)
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)
- James S. McDonnell Foundation
- G. Harold & Leila Y. Mathers Charitable Foundation
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Control over spinal and brainstem somatomotor neurons is exerted by two sets of descending fibers, corticospinal/pyramidal and extrapyramidal. Although in nonhuman primates the effect of bilateral pyramidal lesions is mostly limited to an impairment of the independent use of digits in skilled manual actions, similar injuries in humans result in the locked-in syndrome, a state of mutism and quadriplegia in which communication can be established only by residual vertical eye movements. This behavioral contrast makes humans appear to be outliers compared with other primates because of our almost total dependence on the corticospinal/pyramidal system for the effectuation of movement. Here we propose, instead, that an increasing preponderance of the corticospinal/pyramidal system over motor control is an expected consequence of increasing brain size in primates because of the faster scaling of the number of neurons in the primary motor cortex over the brainstem and spinal cord motor neuron pools, explaining the apparent uniqueness of the corticalization of motor control in humans. (C) 2015 Wiley Periodicals, Inc.
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