Common input across motor nuclei mediating precision grip in humans.

Short-term synchrony was measured for pairs of motor units located within and across muscles activated during a task that mimicked precision grip in the dominant and nondominant hands of human subjects. Surprisingly, synchrony for pairs of motor units residing in separate muscles (flexor pollicis longus, a thumb muscle, and flexor digitorum profundus, an index-finger muscle) was just as large as that for pairs of units both within the thumb muscle. Furthermore, the high level of synchrony seen across muscles in the dominant hand was absent in the nondominant hand. These results suggest that descending pathways diverge to provide extensive common input across motor nuclei involved in the precision grip and that such divergence might contribute to the preferred use of one hand over the other.