Objective: We aimed to probe the parieto-premotor network using transcranial magnetic stimulation (TMS), and further investigate its influence on the motor cortex in patients with writer’s cramp(WC).

Background: The posterior parietal, premotor and motor cortices are brain regions relevant in the planning of movement. Previous TMS studies have shown ipsilateral premotor-to-motor inhibition in healthy subjects at rest. This premotor-to-motor inhibition has been found to be altered in patients with WC, a common type of focal hand dystonia. While altered functional connectivity of the premotor and parietal cortices has been found in resting-state functional magnetic resonance imaging(fMRI), our study investigated this network using TMS.

Method: We aimed to investigate the influence of the posterior parietal cortex on the ipsilateral ventral premotor cortex using a three single-pulse TMS paradigm. Eleven healthy volunteers and eight WC patients completed the study. A three single-pulse TMS paradigm (preconditioning, conditioning and test pulse) was used to sequentially stimulate the left posterior parietal cortex, left ventral premotor cortex, and left primary motor cortices.

Results: We found that in both healthy subjects and WC patients, stimulating the ipsilateral posterior parietal cortex resulted in reversal of the resting premotor-to-motor inhibition. Resting premotor-to-motor inhibition was also found in both groups, with no statistically significant group difference. Furthermore, a facilitatory effect of the posterior parietal cortex on the primary motor cortex was found in both groups.

Conclusion: Our results suggest that in the resting state, the inhibitory effect of the left posterior parietal cortex on the ipsilateral ventral premotor cortex found in healthy subjects is also intact in WC patients. This is the first TMS study to evaluate the effective connectivity between the posterior parietal cortex and ventral premotor cortices in patients with focal hand dystonia.While we are unable to identify any abnormality in the rest state, an abnormality during a specific task cannot be excluded. Previously reported conductivity abnormalities in resting fMRI does not appear to translate into a TMS physiological abnormality.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/probing-the-parieto-premotor-network-in-writers-cramp-using-transcranial-magnetic-stimulation/