Elsevier

NeuroImage

Volume 8, Issue 2, August 1998, Pages 163-175
NeuroImage

Regular Article
Modulation of Corticospinal Output to Human Hand Muscles Following Deprivation of Sensory Feedback

https://doi.org/10.1006/nimg.1998.0352Get rights and content

Abstract

Excitability and conductivity of corticospinal tracts of 10 volunteers were investigated by motor-evoked potentials (MEPs) to transcranial magnetic brain stimulation, before and after anesthetic block of right median (sensory + motor) and radial (sensory) nervous fibers at the wrist. MEPs were simultaneously recorded from two ulnar-supplied muscles during full relaxation and voluntary contraction. These muscles maintained an intact strength following anesthesia, but they were in a remarkably different condition with respect to the surrounding skin: the first dorsal interosseous muscle (FDI) was totally “enveloped” within the anesthetized area but was still dispatching a normal proprioceptive feedback; the abductor digiti minimi (ADM) was preserving both cutaneous and proprioceptive information. Spinal and peripheral nerve excitability were monitored as well. The sensory deprivation induced short-term changes which selectively took place within the hemisphere connected to the anesthetized hand. The physiological latency “anticipation” of MEPs recorded during active contraction versus relaxation was reduced (P< 0.001) in the FDI, but not in the ADM, when values during anesthesia were compared with preanesthesia values. The FDI cortical representation—as analyzed by a mapping procedure of the motor cortex via focal stimuli of several scalp positions—was significantly (P< 0.002) reduced, while the ADM representation remained either unchanged or enlarged. MEP and F-wave variability significantly decreased in the FDI but not in the ADM. F-waves were also affected due to changes in the motoneuronal excitability at spinal level. Peripheral nerve and root stimulation showed no modifications. Results are discussed in view of the short-term modifications of the corticospinal pathway somatotopy produced by the selective reduction of the sensory flow. Implications of the sensory feedback in motor control are also discussed.

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