Sense of muscular effort and somesthetic afferent information in humans

Laboratory and clinical observations of patients with a large-fiber somatic sensory neuropathy indicate a dramatic inability of these patients to set accurate tonic or phasic levels of muscle activity needed to maintain static postures and to reproduce simple movements. These observations 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 performance on weight-matching tasks and discuss new experiments on reaching tasks done by patients with a large-fiber sensory neuropathy and normal controls. In combination, the data show that patients with peripheral sensory deficits exhibit an impaired sense of muscular effort and the consequences of active movement. In addition, the data on weight matching indicate that the basis of disrupted effort sense relates to an inability to correlate psychophysical decisions with concomitant muscle 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 of motor output is mediated in part by peripheral return from somatic sensory afferent systems.