title: Cortical mechanisms of mirror activation during maximal and submaximal finger contractions in Parkinson's disease.
abstract: BACKGROUND
  Mirror movements are often reported in the early stages of Parkinson's disease (PD) and have been attributed to bilateral activation of the primary motor cortex; however, the precise cortical mechanisms are still unclear. Subclinical mirror activation (MA) that accompanies mirror movement has also been reported in healthy aging adults.
  
  
  OBJECTIVE
  To characterize mirror activation and determine the cortical mechanisms of MA in individuals with PD who demonstrate mirror movements.
  
  
  OBJECTIVE
  5 Hz rTMS to the supplementary motor area (SMA) will reduce MA by increasing interhemispheric inhibition (IHI) of the ipsilateral motor cortex.
  
  
  METHODS
  MA was assessed using surface electromyography during maximal and submaximal unimanual contractions of the first dorsal interosseous in 7 individuals with PD with mirror movements (PD-MM: 70.9 ± 13.9 years; UPDRS III: 28.0 ± 8.2), 7 individuals with PD without mirror movements (PD-NM: 71 ± 10.1 years; UPDRS III: 27.8 ± 6.7) and 7 healthy controls (74.4 ± 6.0 years). IHI of the ipsilateral motor cortex was assessed using paired-pulse transcranial magnetic stimulation.
  
  
  RESULTS
  MA was enhanced in both PD groups during submaximal contractions, with the latest onset of activation in PD-NM. Ipsilateral motor cortex excitability was the highest in PDMM; however, IHI did not differ between PD and controls. 5 Hz rTMS to the SMA reduced IHI in PD-NM; however, did not affect MA.
  
  
  CONCLUSIONS
  IHI may not be the sole contributor to the expression of overt mirror movements in PD. Expression of overt mirror movement may be due to the combination of enhanced ipsilateral motor cortex excitability and an earlier onset of electromyographic activation in the mirror hand (mirror activation) in PDMM.
authors.affiliation: Department of Kinesiology, Wilfrid Laurier University, Waterloo, ON, Canada.
authors.forename: Simon A
authors.initials: SA
authors.lastname: Sharples
authors.affiliation: Department of Kinesiology, Wilfrid Laurier University, Waterloo, ON, Canada Sun Life Financial Movement Disorders Research & Rehabilitation Centre, Wilfrid Laurier University, Waterloo, ON, Canada.
authors.forename: Quincy J
authors.initials: QJ
authors.lastname: Almeida
authors.affiliation: Department of Kinesiology, Wilfrid Laurier University, Waterloo, ON, Canada.
authors.forename: Jayne M
authors.initials: JM
authors.lastname: Kalmar
mesh_terms: D000368:Aged; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005385:Fingers; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction; D009043:Motor Activity / Q000502:physiology*; D009044:Motor Cortex / Q000503:physiopathology*; D009433:Neural Inhibition; D010300:Parkinson Disease / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation
keywords: Parkinson's disease; cortical inhibition; primary motor cortex; transcranial magnetic stimulation