The effect of transcranial direct current stimulation on task processing and prioritisation during dual-task gait

Abstract

The relationship between cognition and gait is often explored using a dual-task gait paradigm, which represents the ability to divide cognitive resources during walking. Recent evidence has suggested that the prefrontal cortex is involved in the allocation of cognitive resources during dual-task gait, though its precise role is unclear. Here, we used anodal and cathodal transcranial direct current stimulation (tDCS) to probe the role of the prefrontal cortex in the control of stride time variability (STV), trunk RoM and cognitive task performance during dual-task gait. As task difficulty has been shown to mediate the dual-task cost, we also manipulated walking speed to see whether the effects of tDCS on dual-task gait were influenced by walking difficulty. Ten adults performed a serial subtraction task when walking at either preferred walking speed or 25 % of preferred walking speed, before and after receiving tDCS of the left prefrontal cortex. Anodal tDCS reduced STV and the dual-task cost on STV and improved cognitive task performance. Cathodal tDCS increased STV and appeared to increase the dual-task cost on STV, but did not affect cognitive task performance. There was no effect of tDCS on trunk RoM, and the effects of tDCS were not mediated by walking speed. The effect of dual-task gait on stride time variability and cognitive task performance was altered by the application of tDCS, and these effects were polarity dependent. These results highlight the role of the prefrontal cortex in biasing task performance during dual-task gait and indicate that tDCS may be a useful tool for examining the role of the cortex in the control of dual-task gait.

Appendix: perceived difficulty of preferred and slow walking speed

Ten (two female) participants walked on a motorised treadmill for 3 min at both preferred walking speed and 25 % of preferred (slow) walking speed whilst performing serial subtractions in sevens. At the end of the 3 min, perceived difficulty for the dual-task was recorded using Borg’s CR10 scale (Borg 1998). Differences in perceived exertion between the two DT gait conditions were examined using a Wilcoxon signed-rank test. The perceived difficulty of performing a serial subtraction task whilst walking at the slow walking speed was higher than performing the same task at preferred walking speed (T = 41, p = 0.021, r = 0.51) (Table 4).

Table 4 Median ± IQR difficulty task difficulty (Borg CR10 scale) across both walking speeds