title: Cortical mapping of the infraspinatus muscle in healthy individuals.
abstract: BACKGROUND
  While cortical representations of intrinsic hand muscles have been extensively studied in healthy individuals, little is known about the representation of proximal upper limb muscles. Improving our understanding of normal shoulder function is important, given that shoulder musculoskeletal disorders affect approximately 20% of the population and are suspected to involve changes in central motor representations. The purpose of the study is to describe the motor representation (motor evoked potentials (MEP) amplitude at the hotspot, map area, normalized map volume and center of gravity) of the infraspinatus muscle in healthy individuals, and to explore the potential influence of hand dominance on this representation (i.e. symmetry of the excitability and of the location of motor map between sides), as well as the effect of age and gender on motor excitability.
  
  
  RESULTS
  Fifteen healthy participants took part in this study. No significant asymmetry between sides was observed for motor excitability (p = 0.14), map area (p = 0.73) and normalized map volume (p = 0.34). Moreover, no side x intensity interaction was found (p = 0.54), indicating similar stimulus response properties. No difference between sides was found in the location of infraspinatus motor representation, either in the mediolateral or anteroposterior axis (p > 0.10). Neither age nor gender influenced aMT (p > 0.58) or MEP size (p > 0.61).
  
  
  CONCLUSIONS
  As the cortical representation of infraspinatus muscles was found to be symmetric between sides, both in terms of excitability and location, comparisons between the intact and affected side could be performed in clinical studies, regardless of whether the dominant or non-dominant side is affected. The next step will be to characterize corticospinal excitability and map parameters in populations with shoulder disorders.
authors.affiliation: Department of Rehabilitation, Faculty of Medicine, Laval University, Quebec City, QC, G1R 1P5, Canada.
authors.forename: Suzy
authors.initials: S
authors.lastname: Ngomo
authors.forename: Catherine
authors.initials: C
authors.lastname: Mercier
authors.forename: Jean-Sébastien
authors.initials: JS
authors.lastname: Roy
mesh_terms: D000328:Adult; D001931:Brain Mapping; D004292:Dominance, Cerebral / Q000502:physiology; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult