Motor cortical excitability during voluntary inhibition of involuntary tic movements

Background: Tics can be voluntarily inhibited. However, the neurophysiology of voluntary tic inhibition remains underexplored. The objective of this study was to explore state-dependent effects of voluntary tic inhibition on M1 excitability. Methods: Neurophysiological assessments (single motor-evoked potentials, corticospinal recruitment curves, short-interval intracortical inhibition, H-reflex) were performed in 14 adults with Tourette syndrome during voluntary tic inhibition and free ticcing. Regressions between behavioral performance and neurophysiological measures were also performed. Results: Voluntary tic inhibition reduced corticospinal excitability: the greater the ability to inhibit tics, the greater was the reduction in excitability. Voluntary tic inhibition was not associated with changes in the excitability of short-interval intracortical inhibition or the H-reflex. Conclusions: Voluntary inhibition of tics reduces the excitability of corticospinal output. The pattern of neurophysiological findings is consistent with a withdrawal of excitation, but not with modulation of the inhibitory interneuronal mechanisms involved in short-interval intracortical inhibition. © 2018 International Parkinson and Movement Disorder Society.