Sensorimotor beta enhancement, not mu suppression, differentiates emotional vs. affectively-neutral content

According to the influential action simulation theory of embodied cognition, we recognize others’ emotions by internally simulating their actions with our own sensorimotor systems. Support for this idea comes from studies using electroencephalography (EEG), which have reported reductions in the power of the mu (8-14 Hz) and beta (16-20 Hz) rhythms over sensorimotor cortex, both when executing one’s own movements and observing the actions of others. Specifically, we have previously found that observation of emotional vs. affectively-neutral whole-body movements is associated with greater mu suppression, driven by reduced responses to emotional actions, as well as increased beta enhancement while viewing neutral actions. However, recent evidence suggests that measurements of these periodic oscillations may be conflated with underlying aperiodic (“1/f-like”) neural activity, which can influence the shape of the EEG power spectrum. Here we examined the relative contributions of mu and beta rhythms using high-density 128-channel EEG (N = 117) during the observation of emotional and neutral point-light displays (PLDs). To control for low-level motion, all PLDs were compared to scrambled versions of the same actions. After removing the aperiodic component from the data, we found significant mu suppression for coherent vs. scrambled PLDs, but not emotional content. However, consistent with our previous findings, there was a significant difference between emotional and neutral PLDs in the beta band (14-19 Hz), reflecting enhanced activity over frontocentral sensors for neutral movements. Together, these data suggest that neural oscillations in the mu and beta bands contribute differentially to distinct aspects of action observation.