Early motor reactivity to observed human body postures is affected by body expression, not gender

The early response to emotional stimuli involves a transient suppression of motor reactivity to favor monitoring of emotionally relevant information. Using transcranial magnetic stimulation (TMS), we have previously shown that viewing emotional body postures induces an early and transient reduction in motor excitability. Yet, it remains unclear whether early motor responses to emotional bodies are automatic or influenced by top-down factors such as task- or gender-related effects. To address these issue, we administered TMS over the right motor cortex (M1) during observation of still pictures of fearful expressions, happy expressions, neutral movements and neutral static body postures, and recorded motor-evoked potentials (MEPs) at an early phase of processing (i.e., at 100-125 ms from stimulus onset). To test gender-related effects, we presented male and female models to male and female participants. To test task-related effects, we asked participants to categorize the different body postures into either four (4AFC: fearful, happy, neutral movements, or static postures) or two distinct categories (2AFC: emotional or neutral postures). Results showed a reduction of MEPs for fearful and happy body postures relative to neutral movements and static postures. This motor suppression was not influenced by the gender of the actor, the gender of the observer, or the task performed. These findings indicate that early motor responses to observed human body postures are affected by the type of expression displayed by the observed model more than by task- or gender-related effects, suggesting these responses may be relatively automatic.