As apparent as real: alpha and beta bands desynchronization unveils apparent motion perception dynamics

It is well-known that real motion observation engages sensorimotor processes, so that when biological motion is presented, greater activation of the sensorimotor systems is measured in the observer compared to when non-biological motion is displayed. However, it remains unclear whether apparent motion, perceived from sequences of static images, relies on a similar neural mechanism. A typical blueprint of human action observation is illustrated by the electrophysiological recording of mu rhythm desynchronization, i.e., a power drop in alpha and beta frequency bands over sensorimotor cortices. In this study, by exploiting electroencephalography, we investigated whether apparent motion induces mu rhythm desynchronization when biological (but not non-biological) agents are observed, as usually recorded during real motion observation. Participants observed apparent rotations performed by biological (human hands) or non-biological (pseudo-hands) agents and reported the perceived direction of such rotations. In line with previous findings, our psychophysical results confirmed that only biological stimuli showed a preferential perceived direction of the rotation, compatible with biomechanical constraints that rule real movements. Electrophysiological data revealed significant mu desynchronization, with significantly greater drop for biological than non-biological agents. Taken together, our results suggest that apparent and real motion, when biological agents are involved, induce a similar motor resonance, as if the (real or apparent) action were performed rather than merely observed.