Abstract
Motor-point stimulation using insulated microelectrodes has been used to assess the cerebral pro jection from a number of single muscles in the human upper limb. Previous studies with intrafascicular neural stimulation have revealed a short-latency cortical projection from group I muscle afferents of intrinsic muscles of the hand but this technique is unsuitable to study the projection ofafferents from proximal muscles. In 6 subjects, stimuli were delivered to the motor point of the following muscles: anterior deltoid, biceps brachii (short head), flexor carpi radialis, extensor digitorum communis, abductor pollicis brevis and first dorsal interosseous. The mean latency of the early cortical negativity was l5.Oms for deltoid, l6.4ms for biceps, l8.8ms for flexor carpi radialis, 18.8ms for extensor digitorum communis, 21.9ms for abductor pollicis brevis and 25.Oms for first dorsal interosseous. The amplitude of cerebral potentials from individual muscles was smaller than that produced by stimulation of the digital nerves of the index or little finger and did not vary systematically between proximal and distal muscles. This study provides direct evidence for a short-latency cortical projection from proximal muscles of the upper limb. The results are consistent with psychophysical studies which have proposed a role for intramuscular receptors in kinaesthesia at both proximal and distal joints.

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