Your emotion moves into my motor system

In the present PhD thesis, using Transcranial Magnetic Stimulation, we tested the role of the motor system on visual recognition of emotional body expression. We tested both right and left primary motor cortices (M1) from 100 to 300 ms after stimulus onset. Our findings outline a 3-stage model of the motor system’s involvement in processing others’ emotions. In the first stage (100 ms), we find that, regardless of the stimulated hemisphere, the facilitatory intracortical connections are inhibited when subjects observe fearful stimuli, suggesting the existence of fast motor reactions that we interpret as suppression of motor readiness when seeing potentially harmful stimuli. At a second stage (150 ms), the right M1 shows an inhibitory modulation that is independent of the emotional meaning of the stimuli. We interpret this response, which is also paralleled by a general drop in categorization accuracy, as the sign of an orienting reaction toward emotionally relevant stimuli. In the meantime, left M1 shows a facilitatory response to negative stimuli to prepare a motor reaction of the dominant hand. In the last stage (300 ms), we bilaterally record sign of motor simulation of the implied motion of the stimuli. Our data demonstrate that, as proposed by evolutionary theorists, fast reactions towards threat-related stimuli are detectable in the motor system. On the other hand, as proposed by embodied simulation theorists, we found motor resonance processes observing dynamic stimuli. However, our data show that motor resonance processes are not necessary to extract the emotional meaning of such stimuli