Anodal high-definition transcranial direct current stimulation over the left (but not right) parietal cortex facilitates mental arithmetic

Non-invasive brain stimulation (NIBS) techniques such as transcranial direct current stimulation (tDCS) allow investigating the causal involvement of specific brain areas in mental arithmetic. In this study, we utilized for the first time the enhanced spatial precision of high-definition (HD)-tDCS to study the functional involvement of the left and right intra-parietal sulcus (IPS) in mental arithmetic. A total of 25 participants underwent anodal left IPS, right IPS, and sham stimulation in separate sessions in counterbalanced order while solving single- and multi-step addition and subtraction problems. We found that left but not right IPS stimulation (vs. sham) improved performance across all types of problems. Notably, the observed improvements in arithmetic performance were specific to arithmetic processing, as IPS stimulation had no enhancing effect on performance in a control n-back task. These results provide further evidence supporting the functional involvement of the left IPS in arithmetic problem-solving across a wide range of problem types, and for the use of NIBS for cognitive enhancements.