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Anodal tDCS of the primary motor cortex selectively reduces action processing in ecological discourse

Agustina Birba

  • Victoria,,
  • Argentina
  • Agustina Birba ¹
  • , Francesca Vitale ²
  • , Iván Padrón ²
  • , Martín Dottori ¹
  • , Manuel de Vega ²
  • , Máximo Zimerman ³
  • , Lucas Sedeño ⁴
  • , Agustín Ibáñez ¹
  • 1 Universidad de San Andrés, Buenos Aires, Argentina
  • 2 Instituto Universitario de Neurociencia (IUNE), Universidad de La Laguna, Tenerife, Spain
  • 3 Institute of Cognitive and Translational Neuroscience (INCYT), INECO Foundation, Favaloro University, Buenos Aires, Argentina
  • 4 National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina

Non-invasive stimulation of the primary motor cortex (M1) modulates processing of decontextualized action words and sentences. This suggests that language comprehension hinges on brain circuits mediating the bodily experiences evoked by verbal material. Yet, despite its relevance to constrain mechanistic language models, such findings fail to reveal whether and how relevant circuits operate in the face of everyday texts. Using a novel naturalistic discourse task, we examined whether direct modulation of M1 excitability influences the processing of narrated actions. Following random group assignment, participants received anodal or sham transcranial direct current stimulation over the left M1 or anodal stimulation of the left ventrolateral prefrontal cortex. Immediately afterwards, they listened to action-laden and neutral stories and answered questions on information realized by verbs and circumstances. Anodal stimulation of the left M1 selectively decreased outcomes on action- relative to non-action information –a pattern that discriminated between stimulated and sham participants with 74% accuracy. This result was particular to M1 and held irrespective of the subjects’ working memory and vocabulary skills, attesting to its specificity. Our findings suggest that modulation of motor-network excitability might lead to transient unavailability of putative resources needed to evoke actions in naturalistic texts, opening promising avenues for the language embodiment framework.