Objective: In the current study, our aim was to determine if there occurred task-specific changes in functional connectivity within the task-specificity network for handwriting in writer’s cramp patients compared to healthy controls. We also wanted to determine whether motor imagery of writing induced similar changes in connectivity.

Background: Dystonia in writer’s cramp (WC) is extremely task specific and appears only during planning and executing of writing but not during similar task like pencil sharpening which involves the use of similar object and muscle groups. WC patients show decreased activation of contralateral premotor and posterior parietal areas of the cortex during writing but not during other motor tasks. Parietal-premotor connectivity is also reduced in WC patients. Just motor imagery of writing itself could induce abnormally high levels of dorsal premotor activation in WC patients. However, there is no study that has evaluated the changes in functional connectivity during motor imagery of writing in these patients.

Method: We recruited 15 WC patients and an equal number of age- and gender- matched healthy controls. The subjects sat on a chair in front of a computer screen and performed one of the 4 tasks for 10s (‘write’, ‘sharpen’, ‘imagine writing’ or ‘imagine sharpening’) as per the instruction displayed on the screen in a random order. There was 10s rest between the consecutive trials. 32-channel EEG was recorded and time frequency analysis was done to calculate the power and coherence. Task-related power/coherence was calculated by subtracting normalized power/coherence during rest from that during task.

Results: The alpha and beta power at rest over bilateral motor, contralateral premotor and parietal regions were similar in WC patients and healthy controls. Task-related decrease in beta power was lower in WC patients for motor tasks but not for motor imagery tasks. We also found that the task-related alpha coherence between the two primary motor cortices, and that between contralateral premotor and primary motor cortices were lower in patients.

Conclusion: We have demonstrated a significant decrease in interhemispheric and premotor-motor connectivity during writing in WC patients. Whether the decrease in connectivity correlates with the loss of inhibition and how these changes relate to disease pathophysiology needs to be explored in future studies.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/reduced-interhemispheric-and-premotor-motor-connectivity-during-handwriting-in-patients-with-writers-cramp/