title: Digit-specific aberrations in the primary somatosensory cortex in Writer's cramp.
abstract: OBJECTIVE
  One approach to the treatment of focal hand dystonia (FHD) is via sensory-based training regimes. It is known that FHD patients demonstrate a reduced distance between the representations of digits 1 and 5 and also digits 2 and 5 in primary somatosensory cortex. However, we lack information on the spatial relationships among digits, such as reduced inter-digit spacing or shifts of representations within the cortical areas, and whether aberrations are specific to symptomatic digits. Our aim was to characterize the spatial relationships among individual digits to determine the types of aberrations that exist and whether these are specific to symptomatic digits only.
  
  
  METHODS
  Using high-resolution fMRI over a limited volume and surface-based mapping techniques, the cortical representations of all digits of the dystonia-affected hand within the sub-regions of the postcentral gyrus were mapped in patients with task-specific Writer's cramp (WC).
  
  
  RESULTS
  In area 3b, digits directly involved in writing (D1, D2 and D3) show reduced inter-digit separation, reversals, and overlapping activation. The thumb representation occupies territory normally occupied by digit 2 in controls. Asymptomatic digits 4 and 5 preserve their inter-digit separation yet shift towards the D1/D2/D3 cluster, suggesting that reduced spacing, not simply digit shifts, are associated with dystonia symptoms. Area 3a was less responsive to sensory input in WC patients providing evidence of reduced afferent drive or top-down modulation to this sub-region.
  
  
  CONCLUSIONS
  Therapeutic regimes aimed at facilitating inter-digit separation of digits 1, 2 and 3 may promote beneficial plasticity in WC patients.
authors.affiliation: Toronto Western Research Institute, University of Toronto, Toronto, Canada.
authors.forename: Aimee J
authors.initials: AJ
authors.lastname: Nelson
authors.forename: David T
authors.initials: DT
authors.lastname: Blake
authors.forename: Robert
authors.initials: R
authors.lastname: Chen
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D020821:Dystonic Disorders / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D005385:Fingers; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009473:Neuronal Plasticity; D013003:Somatosensory Cortex / Q000473:pathology / Q000503:physiopathology*; D014956:Writing