Cerebellar engagement in an action observation network.

The cerebellum has traditionally been viewed as a brain structure subserving skilled motor behaviors. However, the cerebellum might be involved not only in movement coordination, but also in action observation and understanding of others' actions. Veridical visual perception of human body motion is of immense importance for a variety of daily-life situations and for successful social interactions. Here, by combining visual psychophysics with a lesion analysis, we assessed visual sensitivity to human walking in patients with lesions to the left cerebellum. Patients with left lateral cerebellar lesions exhibit deficits in visual sensitivity to body motion, whereas medial lesions do not substantially affect visual perception of human locomotion. The findings point to left lateral cerebellar involvement in an action observation network. We discuss possible mechanisms of cerebellar engagement in visual social perception revealed by body motion.