Transcranial Direct Current Stimulation of the Dorsolateral Prefrontal Cortex Enhances Dual-task Performance in People with Stroke

Stroke often results in impaired control of lower limb movement, leading to abnormal gait patterns. During daily activities, walking in the community typically involves performing additional cognitive tasks simultaneously, such as remembering directions or engaging in social interactions. Individuals with stroke are particularly susceptible to dual-task interference and demonstrate a slower gait speed, decreased walking adaptability (e.g., obstacle avoidance), and poorer cognitive task performance during dual-task walking, which can increase the dual-task cost (DTC). Transcranial Direct Current Stimulation (tDCS) is a potential tool to reduce DTC, leading to behavioral modifications and improved cognitive functions. This study aims to investigate the effects of a single session of tDCS targeting the left dorsolateral prefrontal cortex (DLPFC) on dual-task walking performance in individuals with chronic stroke.

The study will be a repeated measure designed with two testing sessions (same time in a day, 7 ± 2 days apart between sessions). People with stroke fulfilling the inclusion and exclusion criteria will be recruited from the local community. In each session, active or shame tDCS will be administered first, followed immediately by randomly assigned single and dual tasks. The stimulation will be delivered using a current stimulator (DC-STIMULATOR MOBILE, NeuroConn, Germany). The intensity is set at 2 mA for 30 min. The anode will be placed over the left DLPFC (F3 according to the EEG 10/20 system), while the cathode over the contralateral supraorbital ridge. The gait measurement is recorded by the Opal IMU sensor module and MobilityLab system (APDM Inc., USA).

Measurements of mobility will consist of two walking conditions: single-task and dual-task walking. For the walking test, we perform 'Stand and Walk for a 20-meter Round Trip (10 meters each way)(SWR), which consists of standing for 10 s, walking 10 m, turning, and walking 10 m back. The total time (TT) taken to complete one SWR test will be recorded. For the single cognitive tasks, participants will remain seated and perform the following: Random number, Word association, Counting forward, Serial subtraction. The time taken to complete each task will be equivalent to the TT recorded during the SSWR test. Additionally, the number of correct responses and errors made during the cognitive tasks will be recorded for further analysis. For the dual tasks, we will combine motor and cognitive tasks to assess dual-task performance. The specific dual tasks include SWR + Random Number, SWR + Word Association, SWR + Counting Forward, SWR + Serial Subtraction, SWR + Head Turns, and SWR+ Visual Fixation. The time taken to complete each task and the number of correct responses and errors made will be recorded for further analysis.

The primary outcomes include gait speed (m/s), stride length (m), and dual-task costs (DTC) for mobility and cognition speed. Each session will last approximately 60 min, including both tDCS and MobilityLab setup, and rest.

The findings may provide valuable insights into the use of tDCS as an adjunctive treatment for stroke patients. By enhancing the cortical activity of the left DLPFC through tDCS, it is anticipated that the dual-task cost would be reduced, which results in better dual-task performance and an improvement in daily function and overall quality of life for stroke survivors.