Effects of single-session cathodal transcranial direct current stimulation on tic symptoms in Tourette's syndrome

Tourette syndrome is a neurodevelopmental disorder characterised by motor and phonic tics. For some, tics can be managed using medication and/or forms of behavioural therapy; however, adverse side effects and access to specialist resources can be barriers to treatment. In this sham-controlled brain stimulation study, we investigated the effects of transcranial direct current stimulation (tDCS) on the occurrence of tics and motor cortical excitability in individuals aged 16-33 years with Tourette syndrome. Changes in tics were measured using video recordings scored using the RUSH method (Goetz et al. in Mov Disord 14:502-506, 1999) and changes in cortical excitability were measured using single-pulse transcranial magnetic stimulation (spTMS) over the primary motor cortex (M1). Video recordings and spTMS measures were taken before and after 20 min of sham or active tDCS: during which cathodal current was delivered to an electrode placed above the supplementary motor area (SMA). Tic impairment scores, calculated from the video data, were significantly lower post-cathodal stimulation in comparison with post-sham stimulation; however, the interaction between time (pre/post) and stimulation (cathodal/sham) was not significant. There was no indication of a statistically significant change in M1 cortical excitability following SMA stimulation. This study presents tentative evidence that tDCS may be helpful in reducing tics for some individuals, and provides a foundation for larger scale explorations of the use of tDCS as a treatment for reducing tics.