P 56. Modulating arithmetic performance: A tDCS/EEG study

Abstract

Research has shown that smaller arithmetic problems (3 + 4) are predominantly solved by retrieving the answer from memory, while larger problems (29 + 14) are solved by applying procedures (e.g. counting, transformation). Furthermore, it has been shown that both types of problems are reflected by differential brain activation in the left posterior parietal cortex (LPPC) and by distinct oscillatory correlates in the electroencephalogram (EEG). Although recent evidence suggests that transcranial direct current stimulation (tDCS) applied over the LPPC might lead to beneficial effects in solving larger problems, little is known about the effects of tDCS on the performance in smaller problems or on the oscillatory EEG activity in larger and smaller problems. Our aim of the present study was to broaden the understanding of the effects of anodal tDCS applied over the LPPC on the performance in arithmetic problems characterized by differential strategy usage (i.e. smaller and larger arithmetic problems). Moreover, we recorded EEG during the arithmetic task to evaluate the oscillatory correlates of tDCS-induced changes in cognitive performance generally and arithmetic performance in particular. To this end, in the present study, twenty-six participants underwent anodal (30 min, 1.5 mA, applied over LPPC) and sham tDCS at two sessions. EEG was recorded while the participants solved smaller and larger arithmetic problems. We examined the effect of tDCS on arithmetic problem solving (solution rate and response latency) and the event-related synchronization and desynchronization (ERS/ERD) in the theta (4–7 Hz), lower alpha (8–10 Hz), and upper alpha (10–12 Hz) frequency bands. Statistical analyses revealed that in large problems response latency was decreased and lower alpha ERD was increased after anodal compared to sham stimulation. In small problems, a decreased solution rate accompanied by a decreased (predominantly left-hemispheric) theta ERS after anodal compared to sham stimulation was found. The former might be explained by increased attentional processes while solving large problems, whereas the latter might reflect increased retrieval interference. Taken together, the results of the present study suggest that anodal tDCS applied over the LPPC modulates performance during mental arithmetic as well as the underlying oscillatory EEG activity in a problem-specific way. Therefore, tDCS in combination with EEG constitutes a promising tool to study the behavioral and neuronal basis of mathematical skills.