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

Abstract

Learning associations between words and their referents is crucial for language learning in the developing and adult brain and for language re-learning after neurological injury. Non-invasive transcranial direct current stimulation (tDCS) to the posterior temporo-parietal cortex has been suggested to enhance this process. However, previous studies employed standard tDCS set-ups that induce diffuse current flow in the brain, preventing the attribution of stimulation effects to the target region. This study employed high-definition tDCS (HD-tDCS) that allowed the current flow to be constrained to the temporo-parietal cortex, to clarify its role in novel word learning. In a sham-controlled, double-blind, between-subjects design, 50 healthy adults learned associations between legal non-words and unfamiliar object pictures. Participants were stratified by baseline learning ability on 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 phases in both HD-tDCS conditions. However, active HD-tDCS resulted in faster retrieval of correct word-picture pairs. Our findings corroborate the critical role of the temporo-parietal cortex in novel word learning, which has implications for current theories of language acquisition.

Common and unique effects of HD-tDCS to the social brain across cultural groups

“…With the current focus on improving the replication of results in psychology (Open Science, 2015), the replicable effects of social brain stimulation provide strong evidence for regional and task specific roles of the dmPFC and rTPJ in self other processing. Evidence for HD-tDCS as an effective tool for studying and potentially improving social cognition aligns with previous research using HD-tDCS in language, cognitive control, and motor domains (Bortoletto et al, 2016;Gbadeyan et al, 2019;Perceval, Martin, Copland, Laine, & Meinzer, 2017). Also, replicated robust effects of HD-tDCS helps dispel claims regarding the effectiveness of tDCS to have any meaningful effect on cognition (Horvath, Forte, & Carter, 2015).…”

tDCS-induced episodic memory enhancement and its association with functional network coupling in older adults

“…Previous studies that used anodal tDCS over the left temporoparietal cortex to modulate associative learning and memory have reported benefits for performance of young adults 25,26,32 . For example, Flöel et al .…”

The Margins of the Language Network in the Brain

“…In principle, it relies on the dynamic mechanisms of pragmatics, resulting in the fact that each pragmatic operation, such as the context-specific modification of a word meaning, leaves some traces in the semantic system of the mental lexicon. The neural substrate of this process seems to involve temporoparietal regions attached to the dorsal path of language processing as indicated by studies on word learning using transcranial electrical DC stimulation (Perceval et al, 2017). In order to further understand these dynamic processes, the nature of concepts and mental objects has to be considered (Mahon and Hickok, 2016), as well as attempts to explain ongoing changes in the mental lexicon in terms of "exemplar" theories assuming that concepts are represented as remembered category instances during category learning (Murphy, 2016).…”