High-definition tDCS of the temporo-parietal cortex enhances access to newly learned words

Learning associations between words and their referents is crucial for language learning in thedeveloping and adult brain and for language re-learning after neurological injury. Non-invasivetranscranial direct current stimulation (tDCS) to the posterior temporo-parietal cortex has beensuggested to enhance this process. However, previous studies employed standard tDCS set-upsthat induce diffuse current flow in the brain, preventing the attribution of stimulation effects to thetarget region. This study employed high-definition tDCS (HD-tDCS) that allowed the current flow tobe constrained to the temporo-parietal cortex, to clarify its role in novel word learning. In a shamcontrolled,double-blind, between-subjects design, 50 healthy adults learned associations betweenlegal non-words and unfamiliar object pictures. Participants were stratified by baseline learning abilityon a short version of the learning paradigm and pairwise randomized to active (20 mins; N = 25) or sham(40 seconds; N = 25) HD-tDCS. Accuracy was comparable during the baseline and experimental phasesin both HD-tDCS conditions. However, active HD-tDCS resulted in faster retrieval of correct word-picturepairs. Our findings corroborate the critical role of the temporo-parietal cortex in novel wordlearning, which has implications for current theories of language acquisition.