Abstract
Human body movements provide important information about the intentions and emotions of others, and growing evidence suggests that we understand others’ mental states by internally recreating, or simulating, their external actions. Research using electroencephalography (EEG) has found reductions in oscillatory “mu” rhythms (8-14 Hz) over sensorimotor cortex both for executed and observed movements. Yet, because previous studies have compared a small subset of electrodes without controlling for visual and attentional factors, questions remain about the respective contributions of perceptual and motor systems to action simulation. Additionally, the effect of emotional content on mu suppression has been relatively unexplored, despite the putative role of action simulation in emotion perception. Here we used high-density EEG to directly compare brain activity associated with motor execution and action observation. In separate blocks, participants (n = 31) completed a finger-tapping task and observed point-light displays (PLDs) of emotional and affectively neutral body movements. Low-level motion information was controlled by contrasting biologically plausible coherent and scrambled PLDs, and attention was maintained through a continuous one-back monitoring task. Motor execution was associated with significant mu suppression (10-14 Hz) over sensorimotor cortex for finger-tapping relative to rest. Comparing action observation for coherent versus scrambled PLDs likewise revealed significant alpha-band suppression in central and frontal sensors, though the average peak frequency of mu suppression was significantly lower (action execution: 11.7 Hz, action observation: 10.8 Hz). Finally, contrasting emotional and neutral body movements, we found no significant differences in sensorimotor mu suppression, but significantly greater alpha suppression over occipital and parietal cortex, perhaps reflecting the greater attentional salience of emotional content. Together, these results generally support the role of sensorimotor systems in action simulation, both for neutral and emotional movements. However, we observed substantial individual variation in the magnitude and distribution of mu suppression, suggesting an avenue for further investigation.