The supplementary effect of transcranial direct current stimulation during upper limb motor practice on consolidation in healthy older adults

Abstract

Background: Ageing affects the consolidation of learned motor skills. Transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex in conjunction with motor sequence learning (MSL) improves consolidation. However, the effects of tDCS of the primary motor cortex (M1) on consolidation are still unclear. Additionally, it seems that the conventional tDCS montage (CONV-tDCS) generates a relatively non-focal stimulation compared to high-definition tDCS (HD-tDCS). So far, it is unknown whether the effects of tDCS depends on its montage. Objective: First, to compare tDCS and sham of the M1 during MSL on dual task (DT) performance as a measure of consolidation. Second, to compare CONV-tDCS and HD-tDCS of the M1 during MSL on DT performance. We hypothesize that tDCS, particularly HD-tDCS, when added to MSL grants superior DT performance compared to sham in older adults. Methods: This study was a sham-controlled randomized double-blind trial with a crossover for tDCS montage. Fifty-two participants were allocated to the active or sham tDCS group. Two sessions of twenty minutes of 1mA tDCS or sham of the M1 were administered during a serial reaction time task (SRTT). DT performance on the SRTT (DT-SRTT) was evaluated by adding an auditory Stroop task. The primary outcome was the mean reaction time on the DT-SRTT after the intervention. Results: The linear mixed model revealed no effect of group (p=.570) or montage (p=.946) on the DT-SRTT. Nevertheless, the mean reaction time of the single task SRTT (ST-SRTT) and DT-SRTT showed a significant improvement over time (p<0.001). Conclusion: DT performance improved with practice in older adults, irrespective of applying tDCS. We conclude that tDCS of the M1 has no surplus benefit on consolidation.