title: Increased motor cortical facilitation and decreased inhibition in Parkinson disease.
abstract: OBJECTIVE
  To identify the changes in motor cortical facilitatory and inhibitory circuits in Parkinson disease (PD) by detailed studies of their time courses and interactions.
  
  
  METHODS
  Short-interval intracortical facilitation (SICF) and short-interval intracortical inhibition (SICI) were measured with a paired-pulse paradigm using transcranial magnetic stimulation. Twelve patients with PD in both ON and OFF medication states and 12 age-matched healthy controls were tested. The first experiment tested the time course of SICF in PD and controls. The second experiment tested SICI at different times corresponding to SICF peaks and troughs to investigate whether SICI was affected by SICF.
  
  
  RESULTS
  SICF was increased in PD OFF state and was reduced by dopaminergic medications. The reduction in SICF from the OFF to ON state correlated with the improvement in PD motor signs. SICI was reduced in PD OFF state and was only partially normalized by dopaminergic medications. At SICF peaks, improvement in SICI with medication correlated with improvement in PD motor sign. Principal component analysis showed that variations of SICF and SICI were explained by the same principal component only in the PD OFF group, suggesting that decreased SICI in the OFF state is related to increased SICF.
  
  
  CONCLUSIONS
  Motor cortical facilitation is increased and inhibition is decreased in PD. Increased cortical facilitation partly accounts for the decreased inhibition, but there is also impairment in synaptic inhibition in PD. Increased cortical facilitation may be a compensatory mechanism in PD.
authors.affiliation: Division of Neurology, Department of Medicine, University of Toronto and the Edmond J. Safra Program in Parkinson's Disease, Toronto Western Research Institute, Krembil Neuroscience Centre, University Health Network, Toronto, Canada.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Ni
authors.forename: Nina
authors.initials: N
authors.lastname: Bahl
authors.forename: Carolyn A
authors.initials: CA
authors.lastname: Gunraj
authors.forename: Filomena
authors.initials: F
authors.lastname: Mazzella
authors.forename: Robert
authors.initials: R
authors.lastname: Chen
mesh_terms: D000368:Aged; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000473:pathology / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D010300:Parkinson Disease / Q000503:physiopathology* / Q000628:therapy*; D050781:Transcranial Magnetic Stimulation / Q000379:methods