High definition tDCS effect on postural control in healthy individuals: entropy analysis of a crossover clinical trial

Objective: The identification of dose-response effects of transcranial direct current stimulation (tDCS) on postural control after stroke has highlighted this strategy as promising for post-stroke rehabilitation. Nonetheless, spatial-temporal dependence data have not been investigated using entropy analysis. Thus, we performed a nonlinear time series analysis of ground reaction force during and after the application of the high-definition transcranial direct current stimulation (HD-tDCS), over the right temporo-parietal junction (TPJ). Materials and Methods: We conducted a randomized, double-blind, placebo-controlled, crossover clinical trial. Twenty-one healthy young adults received the HD-tDCS and sham protocols. We evaluated the exchanging information (causal direction) between both force plates, using the summarized time series of transfer entropy, and compared the dose-response across the healthy subjects by a generalized linear mixed model (GLMM). Results: We found significant variation during the dynamic information flow (p<0.001) among the dominant bodyside. Specifically, all participants were right-handed, and a greater force transfer was observed from the right- to the left-side during the experiment. We observed a causal relationship in the information flow (equilibrium force transfer) from right to left and a decrease in entropy over time. Conclusions: HD-tDCS intervention induced a dynamic influence over time on postural control. Right-TPJ stimulation using HD-tDCS can induce an asymmetry of body weight distribution, leaning to the contralateral side of the stimulation, and thus a plausible post-stroke treatment.