Search Abstracts | Symposia | Slide Sessions | Poster Sessions
Transcranial direct-current stimulation of core language areas facilitates contextual acquisition of spoken and written words: multi-study evidence
Poster Session D, Saturday, October 26, 10:30 am - 12:00 pm, Great Hall 3 and 4
Yury Shtyrov1; 1Aarhus University
We describe a series of experiments aimed at comprehensively assessing effects of transcranial direct current stimulation (tDCS) on word acquisition. tDCS is a non-invasive neurostimulation technique putatively able to shift transmembrane potentials, thereby changing excitation/inhibition thresholds and modulating cortical networks’ capacity for plastic changes. Previous tDCS studies on language have shown disparate results, particularly with respect to language learning and word acquisition. To address this, we systematically investigated effects of tDCS of core left-hemispheric language cortices on neural processes underpinning contextual word learning under different conditions. To this end, prior to a word-learning session, healthy adult participants (N=232) were given 15 minutes of either anodal or cathodal 1.5mA tDCS of Wernicke’s or Broca’s areas, or a control sham/placebo stimulation, in a between-group design. Two sets of experiments were conducted. The first set investigated acquisition of spoken words in implicit inference-based fast mapping (FM) and instruction-based explicit encoding (EE) conditions, balanced for a range of variables. In a word-picture association session, each participant learned 16 novel words either perceptually (via auditory exposure combined with a novel object’s image) or in an articulatory mode (where participants additionally articulated the words overtly). Immediately after this session, learning outcomes were tested using recognition and semantic decision tasks. In both tasks, articulatory learning yielded better results (higher accuracies, shorter latencies) than non-articulatory exposure. EE and FM regimes, in turn, produced generally similar outcomes, indicating their comparable efficiency. Most importantly, real tDCS of both polarities led to global learning improvements, demonstrated by faster (as opposed to sham) reactions and higher accuracies. We also found more specific tDCS effects: better word-recognition accuracy for EE vs. FM after cathodal stimulation, and more expressed improvements in recognition speed and accuracy for anodal Broca and cathodal Wernicke stimulation (particularly for unarticulated FM items). These learning mode-specific effects support the notion of partially distinct neurobiological mechanisms underpinning EE and FM learning strategies. The second set of experiments targeted acquisition of written words of different semantic types. These were presented visually within short 5-sentence stories, whose context rendered novel words as either concrete or abstract (N=10 each). Their retention was tested both immediately and 24 hours later. The results suggested that both anodal and cathodal tDCS of Broca’s area improve immediate acquisition of novel vocabulary, predominantly affecting abstract semantics. Wernicke tDCS showed a similar pattern: an overall better performance over sham condition, particularly expressed for abstract semantics and cathodal stimulation. Furthermore, cathodal Wernicke (but not Broca) stimulation showed enhanced retention of abstract semantics 24 hours later. These results indicate a prominent role of core language areas in encoding abstract words and support the notion of distinct networks for concrete and abstract semantics. To conclude, tDCS of core language cortices exerts a general facilitatory effect on word acquisition with some specificity to learning regimes and word types. Overall, the results of these studies speak to existence of distinct neural networks underlying different learning strategies and different types of semantics. Furthermore, they may inform future applied research into ameliorating learning deficits and language disorders.
Topic Areas: Language Development/Acquisition, Meaning: Lexical Semantics