Enhancement of semantic integration reasoning by tRNS

The right hemisphere is involved with the integrative processes necessary to achieve global coherence during reasoning and discourse processing. Specifically, the right temporal lobe has been proven to facilitate the processing of distant associate relationships, such as generating novel ideas. Previous studies showed a specific swing of alpha and gamma oscillatory activity over the right parieto-occipital lobe and the right anterior temporal lobe respectively, when people solve semantic problems with a specific strategy, i.e., insight problem-solving. In this study, we investigated the specificity of the right parietal and temporal lobes for semantic integration using transcranial Random Noise Stimulation (tRNS). We administered a set of pure semantics (i.e., Compound Remote Associates [CRA]) and visuo-semantic problems (i.e., Rebus Puzzles) to a sample of 31 healthy volunteers. Behavioral results showed that tRNS stimulation over the right temporal lobe enhances CRA accuracy (+12%), while stimulation on the right parietal lobe causes a decrease of response time on the same task (-2,100 ms). No effects were detected for Rebus Puzzles. Our findings corroborate the involvement of the right temporal and parietal lobes when solving purely semantic problems but not when they involve visuo-semantic material, also providing causal evidence for their postulated different roles in the semantic integration process and promoting tRNS as a candidate tool to boost verbal reasoning in humans.