title: Cerebellar stimulation fails to modulate motor cortex plasticity in writing dystonia.
abstract: BACKGROUND
  Primary dystonia is characterized neurophysiologically by reduced inhibitory mechanisms and abnormal regulation of plasticity responses. The potential of anodal cerebellar transcranial direct current stimulation as a therapeutic tool in writing dystonia was examined, after the observation that cerebellar stimulation reduces responses to an associative plasticity protocol in healthy subjects.
  
  
  METHODS
  Ten patients with writing dystonia completed a two-part study (sham and anodal) in which cerebellar stimulation was given simultaneously with paired associative stimulation. Electrophysiological and clinical parameters were measured before and after stimulation.
  
  
  RESULTS
  Clinical symptoms were unchanged by cerebellar stimulation. Patients exhibited much variability in the size and direction of their plasticity responses. Excessive or topographically abnormal plasticity responses were not observed. In the subgroup of patients with facilitatory responses to paired associative stimulation in the sham condition, anodal cerebellar stimulation retained its ability to reduce the magnitude of plasticity response.
  
  
  CONCLUSIONS
  Our limited understanding of intersubject variability of plasticity responses in writing dystonia currently undermines cerebellar stimulation as a novel treatment in this subset of dystonia. Cerebellar stimulation may be beneficial in other neurological disorders with consistently exaggerated plasticity.
authors.affiliation: Shared first authorship, London, United Kingdom; Sobell Department of Motor Neuroscience and Movement Disorders, University College London, London, United Kingdom.
authors.forename: Anna
authors.initials: A
authors.lastname: Sadnicka
authors.forename: Masashi
authors.initials: M
authors.lastname: Hamada
authors.forename: Kailash P
authors.initials: KP
authors.lastname: Bhatia
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Edwards
mesh_terms: D002531:Cerebellum / Q000502:physiology*; D020821:Dystonic Disorders / Q000628:therapy*; D004569:Electroencephalography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014956:Writing
keywords: cerebellar stimulation; cerebellum; plasticity; writers' cramp; writing dystonia