The projection of muscle afferents from the hand to cerebral cortex in man

This study provides direct evidence that muscle afferents from the human hand project to the cerebral cortex. Electrical stimulation within a purely muscle fascicle of the median nerve at the wrist produced a cerebral potential, the latency of which (to the initial negative deflection, N1) was the same as, or shorter than, the latency with stimulation of cutaneous fascicles. The average latencies to N1 for muscle afferent and cutaneous afferent inputs were 19.0 and 20.3 ms, respectively. This difference could not be accounted for by differences in peripheral conduction velocity. The site of the maximal initial negative deflection of the cerebral potential for muscle afferents was posterior to that for cutaneous afferents. This locus for muscle afferents corresponded to that for mixed afferent inputs. Muscle afferents contribute to, and may dominate, the cerebral potential produced by stimulation of the mixed median nerve at the wrist.