Electrophysiology

An EEG study assessing inhibitory control of frontal lobe regions,  which are important for motor inhibition in chronic tic disorders, was conducted using a stop signal task \cite{Zea2022}. Right superior frontal gyrus gamma event-related desynchronization (ERD) was elevated in patients with chronic tic disorder during stop preparation. Elevated right superior frontal gyrus gamma ERD correlated with decreased tic severity, suggesting that right superior frontal gyrus gamma ERD may reflect a mechanism of tic suppression. Using magnetoencephalography, error-related negativity, an event-related potential component and an index of performance monitoring processes during simple stimulus-response tasks, was examined for changes in the performance monitoring system in TS \cite{Metzlaff2022}. The results suggest that increased motor control induced by conflict between high target task performance and tic suppression in TS patients may influence early error-related processing, and that TS patients may initially tend to process all responses as error responses. In the future, it is envisioned that electroencephalography will be useful as a biomarker in TS and in understanding the pathophysiology of tics.
Electrophysiology has also been discussed as a biomarker for tic disorders. TMS was also discussed including reduced short-interval intracortical inhibition at rest, which suggests a correlation with motor tic severity, shortened cortical silent period duration, increased intracortical facilitation, and decreased motor evoked-potential amplitude \cite{Jannati2022}. Using EEG as a biomarker for comprehensive behavioral intervention (CBIT), a randomized controlled trial was conducted to determine whether EEG coherence during Go/NoGo tasks correlated with CBIT outcomes \cite{Morand-Beaulieu2022}. No association was found between EEG coherence during the Go/NoGo task and changes in tic severity, suggesting that brain processes in the inhibition of motor responses do not play any role in CBIT.