Does transcranial direct current stimulation during writing alleviate upper limb freezing in people with Parkinson's disease? A pilot study

Abstract

Transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) can boostmotor performance in Parkinson’s disease (PD) when it is applied at rest. However, the potentialsupplementary therapeutic effect of the concurrent application of tDCS during the training ofmotor tasks is largely unknown. The present study examined the effects of tDCS on upper limbmotor blocks during a freezing-provoking writing task (the funnel task) requiring up- and down-stroke movements at alternating amplitudes. Ten PD patients and 10 age-matched controls un-derwent two sessions of writing combined with 20 min of anodal or sham tDCS on the left M1 in arandomized cross-over design. The primary outcome was the number of upper limb freezingepisodes duringfive trials of the funnel task on a touch-sensitive tablet. PD patients showed asignificant reduction in freezing episodes during tDCS compared to sham. No effects of tDCS werefound for the amplitude, variability and speed of the strokes outside the freezing episodes.However, patients who reported freezing episodes in daily life (N = 6) showed a beneficial effectof tDCS on stroke characteristics. These results indicate a subgroup-dependent variability in re-sponse to non-invasive brain stimulation applied during the performance of motor tasks in PD.This warrants future studies to examine tDCS as an adjuvant tool for training programs aimed toreduce motor deficits related to freezing.