IL RUOLO DEL SISTEMA MOTORIO NELLA COMPRENSIONE VERBALE.

Cognitive science approaches disagree on how the human brain organizes semantic information. Some authors argue that embodied experience is important for conceptual processing and claim that semantic knowledge is grounded on sensory and motor representations; this hypothesis, however, is not universally shared, and the relationship between motor system, language and semantic system is not entirely known. In a TMS experiment, single pulse stimulation was delivered to hand motor cortex 300 or 500 ms after action-related and abstract verbs presentation. The presentation of the same verbs was repeated twice: in this way we investigated the use of cognitive strategies aimed at learning by practice. In the first presentation, stimulation induced facilitation only when TMS was applied 300 ms after action verb presentation. In the second presentation, no modulation was found. In keeping with these results, in a behavioural experiment reaction times were shorter to hand-action related than abstract verbs and this facilitation decreased with practice. These results suggest that motor simulation could contribute to understand action-related rather than abstract verbs. Facilitation is induced only by the early but not by the late stimulation: motor simulation does not seem the result of verb understanding but it would seem directly involved in action verb comprehension, perhaps by facilitating access to semantics. Concerning abstract verbs, motor simulation is not used for comprehension: the access to the semantic meaning could use strategies not involving the motor activation. Finally, with practice the activation of the primary motor cortex is no longer necessary: the meaning of the verb could be automatically retrieved from a lexical-semantic storage without simulation in primary motor cortex. In other words, motor simulation is initially used to retrieve a meaning from the lexical-semantic storage; with practice, the access to semantics is facilitated and motor simulation becomes unnecessary. We explained these data taking into account latest hypothesis on language organization and we tried to overcome dualism between modal and amodal theories on the semantic system.