Interaction between motor commands and somatosensory afferents in the control of prehension.

In 1931, Hughlings Jackson made a distinction between voluntary and automatic movements. According to Jackson the former are varied and purposeful gestures, whereas the latter include stereotyped movements largely under immediate sensory control. In this regard it may be said that the motor function of the primate hand includes both voluntary as well as automatic responses. Phillips and Porter (1977) noted that injury to the nervous system may often disrupt tactile exploration and skilled manipulation, although the same lesion may fail to interfere with automatic prehension used in posture and locomotion. The effects of selective brain destruction as well as the results from single-cell recordings from moving animals have indicated some of the different contributions made by various parts of the cerebello-thalamo-cortical motor system. Prehension offers a unique opportunity in which the interactions between motor commands and somatosensory afferents may be studied.