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Digit-specific aberrations in the primary somatosensory cortex in Writer's cramp
Aimee J Nelson1, David T Blake, Robert Chen
1Toronto Western Research Institute, University of Toronto, Toronto, Canada.
Annals of Neurology
|September 11, 2009
Summary
Focal hand dystonia (FHD) in writer's cramp (WC) involves abnormal spatial maps in the brain. Specifically, symptomatic digits show reduced separation and overlapping activation, guiding new therapeutic approaches.
Area of Science:
- Neuroscience
- Somatosensory Cortex Research
- Motor Control Disorders
Background:
- Focal hand dystonia (FHD) is a neurological disorder affecting fine motor skills.
- Patients with FHD exhibit altered cortical representations in the primary somatosensory cortex.
- Previous studies noted reduced inter-digit distances, but detailed spatial relationships and digit specificity were unclear.
Purpose of the Study:
- To investigate the precise spatial relationships among individual digit representations in the somatosensory cortex of writer's cramp (WC) patients.
- To determine if observed aberrations in cortical maps are specific to symptomatic digits.
Main Methods:
- Employed high-resolution functional magnetic resonance imaging (fMRI) and surface-based mapping.
- Mapped cortical representations of all digits in the affected hand within the postcentral gyrus sub-regions.
- Studied patients diagnosed with task-specific writer's cramp.
Main Results:
- In area 3b, digits 1, 2, and 3 (involved in writing) displayed reduced inter-digit separation, reversals, and overlapping activations.
- The thumb (digit 1) representation encroached upon the area typically occupied by digit 2.
- Asymptomatic digits 4 and 5 maintained normal spacing but shifted towards the symptomatic digit cluster, indicating spacing reduction is key to symptoms.
- Area 3a showed reduced responsiveness, suggesting impaired afferent drive or top-down modulation.
Conclusions:
- Abnormal inter-digit spacing and overlapping representations in area 3b are characteristic of writer's cramp.
- Therapeutic strategies focused on enhancing inter-digit separation for digits 1, 2, and 3 may induce beneficial neuroplasticity in WC patients.
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