Application of Transcranial Direct Current Stimulation (tDCS) to Enhance Attention, Visuo-motor Coordination and Executive Function in Older Adults with Mild Cognitive Impairment

Background: Extensive research had shown executive dysfunction in people with cognitive impairment is associated with functional abnormalities in prefrontal regions such as the right inferior frontal gyrus (Right IFG) or the left dorsal lateral pre-frontal cortex (Left DLPFC). Relevant studies suggest that transcranial direct current stimulation (tDCS) may be a useful therapeutic tool in enhancing attention, visuo-motor coordination and working memory performance.
Method: This study aimed at investigating the effect of tDCS stimulation over left DLPFC or right IFG on attention, inhibition and working memory in people with mild cognitive impairment (MCI) and healthy older adult controls (HC). Recruited participants, aged from 65 to 80 years, included mild cognitive impairment and healthy control older adults. They were randomly divided into experimental and control arms. In experimental arm, participants were randomized to receive either anodal or sham tDCS over the Right iFG or Left DLPFC. tDCS will be administrated in a 2 mA anodal tDCS or sham stimulation to the Left DLPFC or Right IFG for 20 min. Each participant will undergo the performance-based measure of executive function (The Chinese Multiple Errands Test, Chinese MET) before and immediately after the stimulation. During the anodal or sham tDCS stimulation, subjects will perform three neuropsychological tests: Trail Making Task (TMT), Stroop Test (ST) and N-back Task (NBT).
Result: 16 MCI and 16 healthy control, aged 65-80 years were recruited. Linear mixed model analysis using group (HC vs. MCI), stimulation (anodal vs. sham) and region (Left DLPFC vs. Right IFG) as factors were performed. There was significant improvement in TMT, NBT in the group that received the anodal stimulation to Left DLPFC with an effect size of .73 (95% CI = .59-.82) and .76 (95% CI = .65-.81) respectively. Moreover, significant improvement noted in ST when participants received anodal stimulation to Right IFG with effect size of .71 (95% CI = .58-.83).
Conclusion: tDCS showed to be an useful tool in enhancing attention, visuo-motor coordination and working memory performance in older adults with MCI. These pilot findings can be further confirmed by collection of a large sample size as in this on-going study.