title: Low-threshold afferent signalling of viscous loads during voluntary movements of the human digits.
abstract: Humans can discriminate changes in load viscosity during voluntary contractions. The afferent signal origin is unknown. Microneurographic recordings from 83 single low-threshold afferents were made while participants performed triangular ramps either unloaded or with a viscous load. The neural discharges for each cycle were compared across load and velocity. Fifty-eight afferents did not respond. Afferents with sufficient activity were classified as ambiguous--discharges correlated to velocity and load (n=4), infinite viscosity--strong load and weak velocity signal (n=6), no viscosity--strong velocity and weak load signal (n=10) and those with neither (n=5). No single class of afferent provides a coherent signal of viscosity. These data suggest that the central nervous system compares the population response of different inputs to discriminate viscosity.
authors.affiliation: Prince of Wales Medical Research Institute and University of New South Wales, Sydney, Australia. p.mcnulty@unsw.edu.au
authors.forename: Penelope A
authors.initials: PA
authors.lastname: McNulty
authors.forename: Victoria
authors.initials: V
authors.lastname: Galea
authors.forename: James B
authors.initials: JB
authors.lastname: Fallon
authors.forename: Leah R
authors.initials: LR
authors.lastname: Bent
authors.forename: Vaughan
authors.initials: V
authors.lastname: Macefield
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000293:Adolescent; D000328:Adult; D004576:Electromyography / Q000379:methods; D005260:Female; D005385:Fingers / Q000294:innervation*; D006801:Humans; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology*; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009470:Muscle Spindles / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D014783:Viscosity; D016474:Weight-Bearing