SENSE OF MUSCULAR EFFORT AND SOMATESTHETIC AFFERENT INFORMATION IN HUMANS

Laboratory and clinical observations of patients with a large-fiber so matic sensory neuropathy indicate a dramatic inability of these patien ts to set accurate tonic or phasic levels of muscle activity needed to maintain static postures and to reproduce simple movements. These obs ervations suggest that somatic sensation contributes to sensations of motor output, previously thought to be mediated by central mechanisms of corollary discharge. We review data describing psychophysical perfo rmance on weight matching tasks and discuss new experiments on reachin g tasks done by patients with a large-fiber sensory neuropathy and nor mal controls. In combination, the data show that patients with periphe ral sensory deficits exhibit an impaired sense of muscular effort and the consequences of active movement. In addition, the data on weight m atching indicate that the basis of disrupted effort sense relates to a n inability to correlate psychophysical decisions with concomitant mus cle activity. In new experiments, accuracy to match actively achieved arm end points by pointing was decreased in patients with large-fiber sensory neuropathy. The collective results suggest that appreciation o f motor output is mediated in part by peripheral return from somatic s ensory afferent systems.