ABSTRACT
Humans with a large-fiber sensory neuropathy exhibit several abnormalities in movement control, encompassing deficits in postural control, locomotion, and purposive simple or complex limb movements. Accompanying the disordered movements are abnormal patterns of muscle activity often manifested as extremes in co-contraction levels during successful maintenance of steady postures. This indicates that constant motor output is poorly regulated in deafferented patients. It was hypothesized that the fluctuations in motor output exhibited by deafferented patients, as seen in the electromyogram, were related to a poor perceptual appreciation of central nervous system output signals. This was tested by evaluating the sense of muscular effort. Deafferented patients showed an impaired effort sense on several different types of tests and a corresponding lower concordance between psychophysical decisions and the observed muscle activity. This result suggests that appreciation of motor output is mediated in part by peripheral return from somatic sensory afferent systems.
