Lexical ambiguity resolution in Wernicke's area and its right homologue

Introduction: There is an academic dispute regarding the role of the right hemisphere in language processing. Transcranial Magnetic Stimulation (TMS) was used to test the hypothesis that Wernicke's area processes dominant meanings ("teller") whereas its right homologue processes subordinate meanings ("river") of ambiguous words ("bank"; Jung-Beeman, 2005). Methods: Participants were asked to make a semantic decision on ambiguous words that were followed either by unrelated words or by words associated with their dominant or subordinate meanings. A 10 Hz TMS train was applied on each trial over CP5 (left Wernicke), CP6 (right Wernicke) or Cz (vertex) scalp positions, and was synchronized with the word presentation. Results: Accuracy and d′ analysis revealed a TMS LOCATION by MEANING interaction. TMS over Wernicke's area resulted in more accurate responses and higher sensitivity to dominant meaning blocks compared to stimulating the right Wernicke's area and the vertex. In contrast, TMS over the right Wernicke's area resulted in more accurate responses and higher sensitivity to subordinate meaning blocks, compared to stimulating the left Wernicke's area and the vertex. Conclusion: The left and right Wernicke's areas function as processors of dominant and subordinate meanings of ambiguous words, respectively. While previous research methods have yielded indecisive results, TMS proved to be a useful tool in demonstrating a causal role of the two brain regions in a double dissociation design with healthy subjects.