Combining Frontal Transcranial Direct Current Stimulation With Walking Rehabilitation to Enhance Mobility and Executive Function: A Pilot Clinical Trial

Abstract

Objectives: This pilot study assessed whether frontal lobe transcranial direct current stimulation (tDCS) combined with complex walking rehabilitation is feasible, safe, and shows preliminary efficacy for improving walking and executive function.

Materials and methods: Participants were randomized to one of the following 18-session interventions: active tDCS and rehabilitation with complex walking tasks (Active/Complex); sham tDCS and rehabilitation with complex walking tasks (Sham/Complex); or sham tDCS and rehabilitation with typical walking (Sham/Typical). Active tDCS was delivered over F3 (cathode) and F4 (anode) scalp locations for 20 min at 2 mA intensity. Outcome measures included tests of walking function, executive function, and prefrontal activity measured by functional near infrared spectroscopy.

Results: Ninety percent of participants completed the intervention protocol successfully. tDCS side effects of tingling or burning sensations were low (average rating less than two out of 10). All groups demonstrated gains in walking performance based on within-group effect sizes (d ≥ 0.50) for one or more assessments. The Sham/Typical group showed the greatest gains for walking based on between-group effect sizes. For executive function, the Active/Complex group showed the greatest gains based on moderate to large between-group effect sizes (d = 0.52-1.11). Functional near-infrared spectroscopy (fNIRS) findings suggest improved prefrontal cortical activity during walking.

Conclusions: Eighteen sessions of walking rehabilitation combined with tDCS is a feasible and safe intervention for older adults. Preliminary effects size data indicate a potential improvement in executive function by adding frontal tDCS to walking rehabilitation. This study justifies future larger clinical trials to better understand the benefits of combining tDCS with walking rehabilitation.

Keywords: Aging; cognition; rehabilitation; transcranial direct current stimulation; walking.

Figure 1.. CONSORT Flow Diagram

CONSORT Flow Diagram

Figure 2.. Side effect questionnaire for combined walking/tDCS interventions

(A) For each side effect and each group, the percentage of participants who reported a side effect is plotted against the session number. (B) For each side effect and each group, the mean severity rating from all participants in the group is plotted against the session number. For both Panels A and B, shaded graphs (fatigue and bodily pain) pertain mainly to effects of walking, and white graphs pertain mainly to effects of tDCS. Error bars are standard deviation.

Figure 3.. Intervention Step Count

The average number of steps taken during each intervention session is shown for each group. When averaged across all session, the step count for Sham/Typical was 38% higher than Active/Complex (d=1.20) and 17% higher than Sham/Complex (d=0.62).

Figure 4.. Prefrontal activity during walking

According to conceptual models such as CRUNCH (left panel), improvements in task-related prefrontal activity might be characterized by less overactivation during low complexity tasks (e.g., typical walking) and a higher resource ceiling to support performance of more complex tasks (e.g., obstacle walking). The result would be an increased “functional range” of brain activity. For the present experimental groups, this functional range increased from baseline to post-intervention (indicated by dashed lines representing a segment of the CRUNCH curve). The range of prefrontal activity (measured by fNIRS as changes in oxygenated hemoglobin concentration) was increased 0.46μM for Active/Complex, 0.08 for Sham/Complex, and 0.28 for Sham/Typical. However, this study is underpowered for formal statistical analysis.