The effect of motor context on semantic processing: A TMS study

BACKGROUND: Strong embodiment theories claimed that action language representation is grounded in the sensorimotor system, which would be crucially to semantic understanding. However, there is a large disagreement in literature about the neural mechanisms involved in abstract (symbolic) language comprehension. OBJECTIVE: In the present study, we investigated the role of motor context in the semantic processing of abstract language. We hypothesized that motor cortex excitability during abstract word comprehension could be modulated by previous presentation of a stimuli which associated a congruent motor content (i.e., a semantically related gesture) to the word. METHODS AND RESULTS: We administered a semantic priming paradigm where postures of gestures (primes) were followed by semantically congruent verbal stimuli (targets, meaningful or meaningless words). Transcranial Magnetic Stimulation was delivered to left motor cortex 100, 250 and 500 ms after the presentation of each target. Results showed that Motor evoked potentials of hand muscle significantly increased in correspondence to meaningful compared to meaningless words, but only in the earlier phase of semantic processing (100 and 250 ms from target onset). CONCLUSION: Results suggested that the gestural motor representation was integrated with corresponding word meaning in order to accomplish (and facilitate) the lexical task. We concluded that motor context resulted crucial to highlight motor system involvement during semantic processing of abstract language.