Effects of transcranial direct current stimulation combined with concurrent dual-task walking on mobility, gait, and cognitive outcomes: A systematic review

Introduction: Successful execution of normal activities in various populations warrants the performance of dual tasks (DTs). DTs involve motor and cognitive tasking with the involvement of various brain areas. Transcranial direct current stimulation (tDCS) has been used for regulating the excitability of brain cortical regions. The purpose of this review was to evaluate the available scientific evidence on the effects of tDCS combined with concurrent DT walking on mobility, gait and cognition in older adults (OAs) with and without Parkinson's disease (PD). Methods: The PubMed, PEDro, Cochrane Library, Embase and Web databases of Science were searched for relevant articles published from their beginning until date. Randomized controlled trials were retrieved, and their methodological quality and risk of bias were evaluated using the PEDro scale and the Cochrane risk-of-bias tool respectively. Qualitative and quantitative synthesis were used to analyze the data. Results: Five studies were included in the review. The results revealed that in individuals with PD, active tDCS with concurrent DT walking has more potential to significantly improve DT cost to gait speed (p < 0.05), and the proportion of correct responses during DT time up and go test (TUG)_count (p = 0.004). DT walking with concurrent tDCS has potential to significantly improve DT [gait speed _count (p = 0.03), cadence (p = 0.0005), double limb support time (DBST) (p < 0.0001), and single-task (ST) cadence (p = 0.008)]. Significant improvements were observed in the DT costs for stride time (p < 0.0001), DBST (p = 0.03), stride time variability (p < 0.00001), and swing time variability (p = 0.002) with the active tDCS combined with concurrent DT training in OAs. Conclusions: The effects of tDCS combined with concurrent DT walking or training on cognitive, gait and mobility outcomes in OAs with or without PD can be better explained by the DTW training itself. However, tDCS could produce some specific effects in particular outcomes and scenarios.