PMID: 8987754Jan 1, 1997Paper

An electrophysiological study of the postnatal development of the corticospinal system in the macaque monkey

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
E OlivierR N Lemon

Abstract

Postnatal development of the corticospinal system was investigated in 13 macaques using noninvasive transcranial magnetic stimulation (TMS) of the motor cortex and direct electrical stimulation of corticospinal axons in the medullary pyramid and spinal cord. The latency of antidromic corticospinal volleys evoked from the pyramid and recorded from the motor cortex decreased dramatically during the first postnatal months. Our data predict that conduction velocity (CV) of the fastest corticospinal neurons over their cranial course would reach adult values at approximately 11 months. The CV of corticospinal neurons in the spinal cord increased with age but with a slower time course. In the neonate, the fastest spinal CV was estimated at 7.8 m/sec, approximately 10 times slower than in adults (mean 80.0 m/sec). Our data predict that full myelination of corticospinal axons in the spinal cord would not occur until approximately 36 months. No short-latency EMG responses were elicited in arm and hand muscles by TMS until 3 months of age; TMS thresholds were high initially and then fell progressively with age. When corrected for body size, relative latencies of EMG responses showed an exponential decrease during the first postnatal month...Continue Reading

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