According to embodiment theories, understanding the meaning of language involves mentally simulating its content. For example, accessing the meaning of the verb "grab" would imply mentally simulating the movements necessary to grab something. At the neural level, this would translate into recruiting brain regions that control hand movements.
Building on this idea, members of CIMCYC have tested whether inhibiting the motor system affects how people understand the meaning of language. To do this, 30 individuals listened to phrases describing actions related to hands or feet and chose between two possible interpretations of the action. One interpretation was more concrete, based on the motor aspects of the action, while the other was more abstract and based on the goals and consequences of the action. For example, interpretations of the action "turn off the light" were "press a switch" (concrete) and "go to sleep" (abstract).
Before completing the task, transcranial magnetic stimulation (TMS) was applied to the primary motor cortex of the hand (the region that controls hand movement) or to the vertex (a region unrelated to language or movement). This technique involves applying magnetic pulses to the skull, which temporarily inhibit a set of neurons. Based on this logic, it was predicted that inhibiting the hand motor cortex with TMS would make it difficult to represent the motor aspects of hand phrases, leading to a greater choice of abstract interpretations for hand phrases than for foot phrases.
However, the results did not support this hypothesis: participants chose the same number of abstract interpretations for hand and foot phrases, regardless of brain stimulation. Crucially, additional analyses of statistical power and electromyographic activity ensured that the motor cortex had been properly inhibited and that the experiment was able to statistically detect a small effect size.
In conclusion, this study does not support the idea that the primary motor cortex plays a relevant role in how we construct the meaning of language, contrary to what embodiment theories suggest. Future studies should explore the involvement of other motor regions, as well as test other ways of interfering with the motor system, to achieve a better understanding of how the body influences language comprehension.
Full reference:
Solana, P., Escámez, O., Casasanto, D., Chica, A. B., & Santiago, J. (2024). No support for a causal role of primary motor cortex in construing meaning from language: An rTMS study. Neuropsychologia, 108832. https://doi.org/10.1016/j.neuropsychologia.2024.108832
Contact researcher/s:
Pablo Solana (solana@ugr.es)
Ana B. Chica (anachica@ugr.es)
Julio Santiago (santiago@ugr.es)