title: Interhemispheric inhibition of corticospinal projections to forearm muscles.
abstract: OBJECTIVE
  Interhemispheric inhibition (IHI) is typically examined via responses elicited in intrinsic hand muscles. As the cortical representations of proximal and distal muscles in the upper limb are distinguished in terms of their inter-hemispheric projections, we sought to determine whether the IHI parameters established for the hand apply more generally.
  
  
  METHODS
  We investigated IHI at 5 different conditioning stimulus (CS) intensities and a range of short-latency inter-stimulus intervals (ISIs) in healthy participants. Conditioning and test stimuli were delivered over the M1 representation of the right and left flexor carpi radialis respectively.
  
  
  RESULTS
  IHI increased as a function of CS intensity, and was present for ISIs between 7 and 15ms. Inhibition was most pronounced for the 10ms ISI at all CS intensities.
  
  
  CONCLUSIONS
  The range of parameters for which IHI is elicited in projections to the forearm is similar to that reported for the hand. The specific utility lies in delineation of stimulus parameters that permit both potentiation and attenuation of IHI to be assessed.
  
  
  CONCLUSIONS
  In light of evidence that there is a greater density of callosal projections between cortical areas that represent proximal muscles than between those corresponding to distal limb muscles, and in view of the assumption that variations in functional connectivity to which such differences give rise may have important implications for motor behavior, it is critical to determine whether processes mediating the expression of IHI depend on the effector that is studied. This issue is of further broad significance given the practical utility of movements generated by muscles proximal to the wrist in the context of upper limb rehabilitation.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Canada.
authors.forename: R J
authors.initials: RJ
authors.lastname: Ibey
authors.affiliation: School of Psychology, Queen's University Belfast, Northern Ireland, UK. Electronic address: d.bolton@qub.ac.uk.
authors.forename: D A E
authors.initials: DA
authors.lastname: Bolton
authors.affiliation: School of Psychology, Queen's University Belfast, Northern Ireland, UK.
authors.forename: A R
authors.initials: AR
authors.lastname: Buick
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Canada.
authors.forename: W R
authors.initials: WR
authors.lastname: Staines
authors.affiliation: School of Psychology, Queen's University Belfast, Northern Ireland, UK; Trinity College Institute of Neuroscience and School of Psychology, Trinity College Dublin, Ireland.
authors.forename: R G
authors.initials: RG
authors.lastname: Carson
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D005542:Forearm / Q000294:innervation / Q000502:physiology*; D006801:Humans; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Electromyography; Interhemispheric inhibition; Proximal muscles; Transcranial magnetic stimulation; Upper limb