Ten patients with amputation of part of one arm have been studied electrophysiologically. In each patient the ulnar nerve was stimulated electrically in the amputation stump and at a corresponding level in the intact limb. Control observations were also made on 15 normal subject. In the partially-amputated (PA) limbs the amplitudes of the centripetal ulnar nerve compound action potentials, after maximal stimulation of fast-conducting fibres, were markedly reduced in comparison with the results in control limbs. A small decrease in the mean impulse conduction velocity was observed in the population of PA limbs. In comparison with control observations, stimulation of the ulnar nerve in a PA limb evoked responses in the contralateral somatosensory cortex which were significantly diminished. Simulation of PA limbs caused reflex excitation and inhibition of triceps motoneurones similar to that observed in control subjects. In the intact limbs of the amputees, however, inhibition was reduced, possibly as a consequence of overuse. It is concluded that the receipt of an input from the periphery is essential for the functional integrity of most motor and sensory nerve axons, and probably for fibres in the dorsal column-medial lemniscus pathway.
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