Objective: To explore state-dependent effects of voluntary tic inhibition on M1 excitability.

Background: Tics can be voluntarily inhibited. However, the neurophysiology of voluntary tic inhibition remains underexplored. Importantly, the state-dependent effects of voluntary tic inhibition on tic neurophysiology have not been previously experimentally tested.

Methods: Neurophysiological assessments (single MEPs, corticospinal recruitment curves, short-interval intracortical inhibition: SICI, H-Reflex) were performed in fourteen adults with Tourette syndrome during voluntary tic inhibition and a free ticcing state. Clinical regressions between behavioural tic inhibitory performance and neurophysiological measures were also performed.

Results: Voluntary tic inhibition was associated with reduction of M1 excitability. The strength of voluntary tic inhibition showed a linear relation with the amount of M1 excitability change. Neither SICI or H-Reflex accounted for state-dependent findings.

Conclusions: Results are consistent with the idea of an upstream centre that provides voluntary inhibition of tics by reducing the excitability of corticospinal output. This does not appear to involve direct excitation of the inhibitory interneurons that participate in SICI and could therefore represent a withdrawal of excitation.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/motor-cortical-excitability-during-voluntary-inhibition-of-involuntary-tic-movements/