How meaning unfolds in neural time: Embodied reactivations can precede multimodal semantic effects during language processing

GARCÍA, ADOLFO M.; GARCÍA-MARCO, ENRIQUE; CASTILLO, EDUARO; IBÁÑEZ, AGUSTÍN; MOGUILNER, SEBASTIÁN; HERRERA, EDUAR; KLEINESCHAY, TARA; TORQUATI, KATHYA; MUÑOZ, EDINSON; SEDEÑO, LUCAS

NEUROIMAGE.

ACADEMIC PRESS INC ELSEVIER SCIENCE

Lugar: Amsterdam; Año: 2019 vol. 197 p. 439 - 449

1053-8119

Research on how the brain construes meaning during language usehas prompted two conflicting accounts. According to the ´grounded view´,word understanding involves quick reactivations of sensorimotor(embodied) experiences evoked by the stimuli, with simultaneous or laterengagement of multimodal (conceptual) systems integrating informationfrom various sensory streams. Contrariwise, for the ´symbolic view´, thiscapacity depends crucially on multimodal operations, with embodiedsystems playing epiphenomenal roles after comprehension. To test thesecontradictory hypotheses, the present magnetoencephalography studyassessed implicit semantic access to grammatically constrained action andnon-action verbs (n = 100 per category) while measuring spatiotemporallyprecise signals from the primary motor cortex (M1, a core regionsubserving bodily movements) and the anterior temporal lobe (ATL, aputative multimodal semantic hub). Convergent evidence from sensor- andsource-level analyses revealed that increased modulations for actionverbs occurred earlier in M1 (~130-190 ms) than in specific ATL hubs(~250-410 ms). Moreover, machine-learning decoding showed that trial-bytrialclassification peaks emerged faster in M1 (~100-175 ms) than in theATL (~345-500 ms), with over 71% accuracy in both cases. Consideringtheir latencies, these results challenge the ´symbolic view´ and itsimplication that sensorimotor mechanisms play only secondary roles insemantic processing. Instead, our findings support the ´grounded view´,showing that early semantic effects are critically driven by embodiedreactivations and that these cannot be reduced to post-comprehensionepiphenomena, even when words are individually classified. Briefly, ourstudy offers non-trivial insights to constrain fine-grained models oflanguage and understand how meaning unfolds in neural time.