The Effects of Transcranial Direct Current Stimulation to left DLPFC on Attention, Inhibition and Working Memory for People with Dementia

Background: The left dorsolateral prefrontal cortex (DLPFC) is a brain region that has been associated with executive function. In functional perspective, it involves the ability to organize, plan and carry out activities of daily living in an efficient manner. Method: A double-blinded, randomized case-control, single session interventional study was conducted to a match group of 24 older adults with dementia and 24 healthy control. Participants were then randomized to either anodal left DLPFC stimulation or sham stimulation . Those recruited subjects were equally randomized to 4 groups of single intervention, namely experimental verum stimulation, experimental sham stimulation, healthy control verum stimulation and health control sham stimulation. The outcome measures included pre-and-post stimulation performance-based measure of executive function (The Home-based Evaluation of Executive Function; The Home -MET), and three well established experimental paradigms of cognitive psychology such as Trail Making Task (TMT), N-back Task (NBT) and Stroop Test (ST) under different modes of cognitive stimulation. Result: With age and gender as covariates, the repeated measure ANOVAs of the MET results showed a significant group effect within subjects with F(1, 3) = 5.56, p < .01, with small to medium effect size of partial eta square = .28 with observed power = .92 , p < .05. In univariate general linear model analyses, NBT demonstrated there is significant interaction effect between group and types of stimulation, the univariate F(1, 44) = 8.77 with p = .001, small to medium effect size with partial eta square = .37 with observed power = .99. By multi-variate general linear model, NBT and TMT together demonstrated there is significant interaction effect between groups, for NBT, the multivariate F(1, 42) = 9.03, p = .001 with partial eta square = .39 with observed power = .99. Conclusion: In this paper we investigate the effect single-session tDCS may have on impact on performance-based measure and cognition enhancement by using three well established experimental paradigms of cognitive psychology. Significant difference noted between experimental and health control in verum tDCS stimulation. Interesting, the sham tDCS also demonstrated its effect on executive function enhancement in healthy control but not the dementia subjects.