Short CommunicationDoes comprehension of symbolic gestures and corresponding-in-meaning words make use of motor simulation?

- We searched for the processes used to understand the meaning of emblems and words.
- TMS was applied to motor cortex during observation/listening of gestures and words.
- As controls meaningless gestures, pseudo-words and a still actor were presented.
- Motor cortex was activated by presentation of meaningless signals only.
- Understanding emblems and corresponding words probably use semantic circuits.

The present study aimed at determining whether or not the comprehension of symbolic gestures, and corresponding-in-meaning words, makes use of cortical circuits involved in movement execution control. Participants were presented with videos of an actress producing meaningful or meaningless gestures, pronouncing corresponding-in-meaning words or pseudo-words; they were required to judge whether the signal was meaningful or meaningless. Single pulse TMS was applied to forearm primary motor cortex area 150-200 ms after the point when the stimulus meaning could be understood. MEPs were significantly greater when processing meaningless signals as compared to a baseline condition presenting a still-and-silent actress. In contrast, this was not the case for meaningful signals whose motor activation did not differ from that for the baseline stimulus. MEPs were significantly greater for meaningless than meaningful signals and no significant difference was found between gesture and speech. On the basis of these results, we hypothesized that the observation-of/listening-to meaningless signals recruits motor areas. In contrast, this did not occur when the signals were meaningful. Overall, the data suggest that the processes related to comprehension of symbolic gestures and communicative words do not involve primary motor area and probably use brain areas involved in semantics.