Listening to action-related sentences modulates the activity of the motor system: A combined TMS and behavioral study

Transcranial magnetic stimulation (TMS) and a behavioral paradigm were used to assess whether listening to action-related sentences modulates the activity of the motor system. By means of single-pulse TMS, either the hand or the foot/leg motor area in the left hemisphere was stimulated in distinct experimental sessions, while participants were listening to sentences expressing hand and foot actions. Listening to abstract content sentences served as a control. Motor evoked potentials (MEPs) were recorded from hand and foot muscles. Results showed that MEPs recorded from hand muscles were specifically modulated by listening to hand-action-related sentences, as were MEPs recorded from foot muscles by listening to foot-action-related sentences. This modulation consisted of an amplitude decrease of the recorded MEPs. In the behavioral task, participants had to respond with the hand or the foot while listening to actions expressing hand and foot actions, as compared to abstract sentences. Coherently with the results obtained with TMS, when the response was given with the hand, reaction times were slower during listening to hand-action-related sentences, while when the response was given with the foot, reaction times were slower during listening to foot-action-related sentences. The present data show that processing verbally presented actions activates different sectors of the motor system, depending on the effector used in the listened-to action.