Acute effect of transcranial direct current stimulation on postural sway in individuals with Parkinson’s disease

Abstract

Introduction: Transcranial direct-current stimulation (tDCS) has been widely applied for the rehabilitation of Parkinson disease (PD). Objective: In the present study, we asked whether postural sway of PD patients is affected after a single session of tDCS. Methods: PD patients were randomly assigned to a REAL (N=9) or SHAM (N=9) group and asked to stand upright with feet apart or tandem position for 45s each. Balance assessment was made before (pre) and immediately after (post) a single 15min application of anodal-tDCS (1.2mA) applied at the medial motor areas. Center-of-pressure coordinates were acquired through a force platform and transformed in radial distance (RD); RMS, mean frequency and mean velocity were then calculated. Post- minus pre-tDCS (delta-tDCS) was compared (i) with zero-value through one-sample t-test and (ii) between groups with t-test for independent samples. Statistical threshold was set at 5%, corrected for multiple comparisons. Results: For both feet apart and tandem stance tasks, the delta-tDCS was not different from zero-value (all P>0.08), meaning no significant changes in any variable from pre- to post-tDCS. Additionally, no significant between-group differences were found (all P>0.297), although a moderate effect size was attained for RMS during tandem stance (d=0.54), referring to a reduction in postural sway amplitude in REAL (RDRMS=-1.2±2,7mm; mean ±SD) compared to SHAM (RDRMS=0.1±2.5mm) group. In summary, a single-session of tDCS over motor areas has no relevant immediate effect on postural control of PD patients. Conclusion: Accordingly, no special concern regarding the acute effect of low-level electrical stimulation is needed for the design of subsequent balance rehabilitation program in this population.