Cerebellar direct current stimulation enhances motor learning in older adults

Abstract

Developing novel approaches to combat age related declines in motor function is key to maintaining health and function in older adults, a subgroup of the population that is rapidly growing. Motor adaptation, a form of motor learning, has been shown to be impaired in healthy older subjects compared with their younger counterparts. Here, we tested whether excitatory anodal transcranial direct current stimulation (tDCS) over the cerebellum could enhance adaptation in older subjects. Participants performed a "center-out" reaching task, adapting to the sudden introduction of a visual cursor rotation. Older participants receiving sham tDCS (mean age 56.3 ± 6.8 years) were slower to adapt than younger participants (mean age 20.7 ± 2.1 years). In contrast, older participants who received anodal tDCS (mean age 59.6 ± 8.1 years) adapted faster, with a rate that was similar to younger subjects. We conclude that cerebellar anodal tDCS enhances motor adaptation in older individuals. Our results highlight the efficacy of the novel approach of using cerebellar tDCS to combat age related deficits in motor learning.

Keywords: Brain stimulation; Learning; Motor control; Older subjects; Rehabilitation; Transcranial direct current stimulation.

Figure 1

(A) Design of the experiment. The experiment was composed of three phases. In the baseline phase participants completed two blocks of pre perturbation trials. Pre 1 was completed with no stimulation, while Pre 2 was completed with anodal/sham tDCS. In the second phase, a 30° cursor rotation was applied (blocks Adapt 1 and 2). In the third phase participants completed three post adaptation blocks; both the rotation and visual cursor feedback were removed. The numbers within parenthesis represent the number of trials in each block. (B) Shows a schematic of the experimental setup. Participants sat in a robotic exoskeleton device with a monitor and bib blocking vision of their body. They moved their arm to shoot a cursor from a start position through a circular target in one of eight potential positions (other target locations shown by open circles). C) Mean error across epochs for the older sham (white), younger sham (Grey), and older anodal (black) groups. Error bars represent SEM. Shaded region presents the period during which the Older Anodal group received tDCS. Inset presents significant differences between mean group error during the adaptation phase. D) Parameter estimates for the error decay constant λ during the adaptation phase for the three groups (error bars represent 95% confidence intervals). E) Estimates of parameter λ during the post adaptation phase for the three groups. * and ** indicate p<0.05 and p<0.01, respectively.