A randomized sham-controlled trial on the effects of dual-tDCS "during" physical therapy on lower limb performance in sub-acute stroke and a comparison to the previous study using a "before" stimulation protocol

Background: Dual-transcranial direct current stimulation (tDCS) has been used to rebalance the cortical excitability of both hemispheres following unilateral-stroke. Our previous study showed a positive effect from a single-session of dual-tDCS applied before physical therapy (PT) on lower limb performance. However, it is still undetermined if other timings of brain stimulation (i.e., during motor practice) induce better effects. The objective of this study was to examine the effect of a single-session of dual-tDCS "during" PT on lower limb performance in sub-acute stroke and then compare the results with our previous data using a "before" stimulation paradigm.

Method: For the current "during" protocol, 19 participants were participated in a randomized sham-controlled crossover trial. Dual-tDCS over the M1 of both cortices (2 mA) was applied during the first 20 min of PT. The Timed Up and Go and Five-Times-Sit-To-Stand tests were assessed at pre- and post-intervention and 1-week follow-up. Then, data from the current study were compared with those of the previous "before" study performed in a different group of 19 subjects. Both studies were compared by the difference of mean changes from the baseline.

Results: Dual-tDCS "during" PT and the sham group did not significantly improve lower limb performance. By comparing with the previous data, performance in the "before" group was significantly greater than in the "during" and sham groups at post-intervention, while at follow-up the "before" group had better improvement than sham, but not greater than the "during" group.

Conclusion: A single-session of dual-tDCS during PT induced no additional advantage on lower limb performance. The "before" group seemed to induce better acute effects; however, the benefits of the after-effects on motor learning for both stimulation protocols were probably not different. Trial registration Current randomized controlled trials was prospectively registered at the clinicaltrials.gov, registration number: NCT04051671. The date of registration was 09/08/2019.