P 15. Cognitive performance depending on side of transcranial direct current stimulation (tDCS)

Abstract

Introduction. Previous research revealed significant effects of tDCS (transcranial direct current stimulation) over the dorsolateral prefrontal (DLPFC) on cognition. However, the effects of right- vs left-sided stimulation on different cognitive domains has not been sufficiently studied. Therefore, this study aimed at showing differential effects of right- vs left-sided tDCS of the DLPFC on different cognitive domains depending on the stimulated hemisphere. Methods. Healthy participants aged 20 to 35 years were randomly assigned to one of three groups in a double-blinded randomized controlled trial. Participants underwent tDCS either of the left ( N = 20) or the right hemisphere (N=20), or sham stimulation (N=20). A neuropsychological test battery comprising verbal as well as non-verbal tasks covering different cognitive domains was conducted on three consecutive days. Stimulation was scheduled prior to the cognitive assessment on the second day. For this, we used the 10-10 hybrid StarStim 32 EEG-tDCS system with a total inject stimulation current of 2 mA distributed over 5 electrodes (right group: AF4 0.976 mA, F4 0.976 mA as anodes and Fpz −0.731 mA, FC6 −0.730 mA, Cz −0.491 mA as cathodes; left group: AF3 0.999 mA, F3 1.0 mA as anodes and FC5 −0.848 mA, Fpz -.820 mA, Cz −0.331 mA as cathodes). The same system was used to derive an electro encephalogram (EEG) before and after stimulation. Performance directly and 24 hours after stimulation was compared to baseline with repeated measurement ANOVA. For two tests comprising several parameters (verbal memory test “VLMT” and test for attentional and executive functions “EpiTrack”) repeated measurement MANOVA was performed. Results. No significant interactions were found, yet non-verbal working memory (block span) and variability in reaction time of a Go/NoGo paradigm showed a slight effect ( p < .10): Left-sided anodal tDCS inhibited non-verbal working memory directly after stimulation. With anodal stimulation on either side, subjects appeared to benefit less from repetition effects in reducing variability in response times. Conclusion. While left-sided tDCS of the DLPFC slightly inhibited a spatial working memory task, our study found no further indications of cognitive effects specific to the side that was stimulated. Analysis of resting EEG prior and after stimulation might yield neurophysiological correlates for the observed behavior outcomes.