The influence of transcranial alternating current on fluid intelligence. A fMRI study

Abstract

The aim of this study was to investigate the influence of transcranial alternating current stimulation (tACS) on fluid intelligence (gf). Furthermore, the study is the first to explore the relevance of the parietal cortex for fluid reasoning processes by means of tACS and fMRI. In a double-blind sham-controlled experiment 20 participants performed fluid intelligence tasks (matrices task, and paper folding) after theta transcranial alternating current stimulation was applied to the left parietal cortex. Stimulation induced brain activity changes were recorded during the task processing using fMRI. The results indicated a difficulty-specific stimulation effect: When solving difficult items of the matrices test verum tACS significantly increased fluid reasoning performance, as compared to sham tACS. No such difference was observed for items with easy item difficulty. Whole-brain analyses showed that left parietal brain stimulation was accompanied by less right sided activation in the areas of the frontal lobe, the fusiform gyrus and the occipital lobe, as well as left sided in the area of the middle occipital gyrus. Additional ROI analyses revealed a tendency for less activation in the left inferior parietal lobule. The results are discussed within the theoretical framework of the neural efficiency hypothesis as well as of the parieto-frontal-integration theory.