Site-specific decrease in cortical reactivity during sensory trick in cervical dystonia patients.

BackgroundSensory tricks (SeT) are various maneuvers that can alleviate dystonic contractions and are a characteristic feature of cervical dystonia (CD). The neurophysiology underlying SeT, however, remains largely unknown. Reducing the abnormal cortical facilitation and modulating the abnormal cortical and subcortical oscillatory activity are mechanisms that have been proposed. The supplementary motor area (SMA) and primary sensorimotor cortices are thought to be relevant to this phenomenon. ObjectiveIn the current study, using concurrent EEG recording during transcranial magnetic stimulation (TMS) of the SMA and primary motor cortex (M1), we aimed at determining the changes in cortical reactivity and oscillatory changes induced by SeT. MethodsWe recruited 13 patients with CD who exhibited SeT and equal number of age- and gender-matched healthy controls. Single TMS pulses were delivered over the SMA and M1 either at rest or during SeT. 32-channel EEG was recorded, and TMS-evoked potentials (TEP) were obtained. Further, time-frequency analysis was performed on the induced data. Correlation analysis for significant neurophysiological parameters was done with clinical measures. ResultsWe found that SeT induced a significant decrease in the amplitude of TEP elicited from M1 stimulation at [~]210-260ms in patients, which correlated with symptom duration. Post hoc analysis of EMG activity in the neck muscles revealed that this effect on TEP was present only in the subset of patients with effective SeT. ConclusionOur results suggest that SeT reduces cortical reactivity over M1 approximately 200ms after stimulation. This adds support to the idea that reduced cortical facilitation underlies the phenomenon.