Anodal direct current stimulation in the healthy aged: Effects determined by the hemisphere stimulated

Purpose: Research popularity and scope for the application of transcranial direct current stimulation have been steadily increasing yet many fundamental questions remain unanswered. We sought to determine if anodal stimulation of either hemisphere leads to improved performance of the contralateral hand and/or altered function of the ipsilateral hand, or affects movement preparation, in older subjects. Method: In this cross-over, double blind, sham controlled study, 34 healthy aged participants (age range 40-86) were randomised to receive 20 minutes of stimulation to either the dominant or non-dominant motor cortex. The primary outcome was functional performance of both upper limbs measured by the Jebsen Taylor Test and hand grip strength. Additionally, we measured motor preparation using electrophysiological (EEG) recordings. Results: Anodal stimulation resulted in statistically significantly improved performance of the non-dominant hand (p < 0.01) but did not produce significant changes in the dominant hand on any measure (p > 0.05). This effect occurred irrespective of the hemisphere stimulated. Stimulation did not produce significant effects on measures of gross function, grip strength, reaction times, or electrophysiological measures on the EEG data. Conclusion: This study demonstrated that the hemispheres respond differently to anodal stimulation and the response appears to be task specific but not mediated by age.