Effects of a single tDCS session on anticipatory postural adjustments during step initiation in individuals with Parkinson's disease

Abstract

Introduction: During gait initiation anticipatory postural adjustments (APAs) are responsible for a backward and laterally shift of the center of pressure (COP) towards the initial swing limb. In Parkinson disease (DP), APAs are abnormally prolonged in duration and reduced in amplitude with an impairment of the subsequent step. This may be associated with the reduced activity of the supplementary motor area (SMA) found in these individuals. Objective: The main aim of this study was to investigate if a single session of anodal transcranial direct current stimulation (tDCS), a non-invasive, handle and low cost form of brain stimulation, applied over SMA can influence the APAs preceding gait initiation in PD individuals in the ON phase of medication. Methods: This is a randomized, double-blinded, sham-controlled design study. All individuals underwent an exercise program delivered in 10 treatment sessions over 4 weeks (three times per week) to match the level of activity of the group. Twenty-one individuals were randomly assigned to one of the two groups: experimental (n=11) and sham group (n=10). A single session of anodal tDCS (2 mA) was conducted over SMA with each individual of experimental and sham group with the same montage. Immediately before and after the tDCS session, the groups were evaluated using both a posturographic exam (for APAs duration, displacement and velocity preceding step initiation) and motor performance (by UPDRS part III). Results: There were no statistical differences between the two groups for all variables. However, there was a large effect size to step time, S1 time and a medium effect size for velocity of APAs, as the Cohen’s d indicated. As the analyses of the confidence interval suggest, there are trends of a longer duration for both step time and S1time for the experimental as compared to the sham group. Conclusion: These results suggested that a single session of anodic tDCS over SMA promoted trends of increase in APA duration preceding step initiation. Future clinical trials with a bigger sample should be conducted to confirm these founds.