title: Task-related changes in sensorimotor integration influence the common synaptic input to motor neurones.
abstract: OBJECTIVE
  The purpose of this investigation was to understand how visual information, when used to guide muscle activity, influences the frequency content of the neural drive to muscles and the gain of afferent feedback.
  
  
  METHODS
  Subjects maintained static, isometric contractions of the tibialis anterior muscle by matching a visual display of their ankle dorsiflexion force to a target set at 10% of their maximum voluntary contraction level. Two visual feedback conditions were studied. The first was a high-sensitivity feedback, in which small changes in force were of large on-screen visual magnitude. The second was a low-sensitivity feedback, in which the on-screen scaling of feedback was reduced by a factor of 10, making small force fluctuations difficult to perceive. Force tremor and Hoffmann reflex (H-reflex) amplitudes were compared between the two conditions, as well as coherence among single motor unit spike trains derived from high-density EMG recordings.
  
  
  RESULTS
  The high-sensitivity feedback condition was associated with lower error, larger force tremor (4-12 Hz) and larger H-reflex amplitudes relative to the low-sensitivity feedback condition. In addition, the use of high-sensitivity feedback was associated with lower 1-5 Hz coherence among pairs of motor units, but larger coherence at high frequencies (6-12, approx. 20, >30 Hz).
  
  
  CONCLUSIONS
  Alteration of visual feedback influences nearly the entire frequency spectrum of common input to motor neurones, as well the gain of afferent feedback. We speculate that task-related modulation of afferent feedback could be the origin of many of the observed changes in the neural drive to muscles.
authors.affiliation: Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology (BFNT) Göttingen, Bernstein Centre for Computational Neuroscience (BCCN), University Medical Center Göttingen, Georg-August University, Göttingen, Germany.
authors.forename: C M
authors.initials: CM
authors.lastname: Laine
authors.forename: S U
authors.initials: SU
authors.lastname: Yavuz
authors.forename: D
authors.initials: D
authors.lastname: Farina
mesh_terms: D000328:Adult; D004576:Electromyography; D056228:Feedback, Sensory / Q000502:physiology*; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D055815:Young Adult
keywords: Hoffmann reflex; afferent feedback; coherence; motor units