title: Modulation of primary orthostatic tremor by magnetic stimulation over the motor cortex.
abstract: OBJECTIVE
  To study the role of corticomotor neuronal pathways in primary orthostatic tremor.
  
  
  METHODS
  Transcranial magnetic stimuli at an intensity 10% above the resting motor threshold were delivered over the leg motor cortex in two patients with primary orthostatic tremor while standing still. Electromyographic responses in both tibialis anterior muscles were recorded after 20 stimuli given randomly at intervals of 120 to 180 seconds. Differences between predicted and actual times of occurrence of tremor bursts after the stimuli were used to calculate a resetting index, with a value of 0 representing no resetting and a value of 1 representing complete resetting.
  
  
  RESULTS
  Transcranial magnetic stimulation evoked EMG responses in both tibialis anterior muscles, followed by transient suppression of tremor before reappearance of rhythmic EMG activity. Analysis of the timing of tremor bursts from EMG recordings before and after the magnetic stimuli disclosed that the phase of orthostatic tremor could be reset by brain stimulation (mean resetting indices 0.93 and 0.82).
  
  
  CONCLUSIONS
  The results suggest that a central oscillator, involving the motor cortex, has a crucial role in either the generation or modulation of orthostatic tremor.
authors.affiliation: Department of Neurology, Royal Adelaide Hospital, Australia.
authors.forename: C H
authors.initials: CH
authors.lastname: Tsai
authors.forename: J G
authors.initials: JG
authors.lastname: Semmler
authors.forename: T E
authors.initials: TE
authors.lastname: Kimber
authors.forename: G
authors.initials: G
authors.lastname: Thickbroom
authors.forename: R
authors.initials: R
authors.lastname: Stell
authors.forename: F L
authors.initials: FL
authors.lastname: Mastaglia
authors.forename: P D
authors.initials: PD
authors.lastname: Thompson
mesh_terms: D004576:Electromyography; D005260:Female; D006801:Humans; D016014:Linear Models; D008280:Magnetics; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology*; D010812:Physical Stimulation; D011187:Posture; D011237:Predictive Value of Tests; D011930:Reaction Time; D013997:Time Factors; D014202:Tremor / Q000503:physiopathology* / Q000517:prevention & control*