Sun and colleagues explored the suppressive effect of the motor system on the sensory system in TS patients \citep{Sun_2020}. They used a sham-controlled rTMS protocol (1Hz, 90% of the resting motor threshold) and recorded the somatosensory evoked potentials before and 15 minutes after rTMS. If somatosensory evoked potentials amplitudes were decreased for both TS patients and healthy controls, the decrease was stronger for TS patients. They interpreted this finding as a suppressive effect of the motor-sensory system on the sensory system instead of a sole influence of the motor system, and therefore as TS resulting more from a sensorimotor disorder than a sole motor dysfunction.

Neuroimaging studies

Rae and colleagues provide a high-quality study of action inhibition in TS comprising 23 adults with TS and 21 healthy controls using the same intentional inhibition task  \citep{33409490}.  Importantly, the authors chose a task that did not directly involve tics, so both groups could participate equally in inhibiting a movement. Several inhibitory regions were more active in TS, especially right inferior frontal gyrus, plus insula and basal ganglia. Even though participants did not move, the primary cortex was more active during the task in the TS group but less active in the control group. Finally, during a task in which participants decide on their own whether or not to move a finger, premonitory sensations correlated with functional connectivity of the pre-SMA region to caudate, globus pallidus and thalamus.
Hippocampal volume was increased both in TS and in 41 children with provisional tic disorder (PTD) compared to tic-free control children \citep{jcm9061715}. Since the PTD group was studied a mean of only 4 months after  tic onset, this difference cannot be due to living with or adapting to tics for years, an advantage over all studies in TS itself. Excitingly, in the PTD group, a larger hippocampus at the initial visit predicted worse tic severity at one-year follow-up, comprising the first predictive biomarker identified for PTD \citep{jcm9061715}. Surprisingly, striatal volume at baseline did not predict tic severity at follow-up.