Action perception recruits the cerebellum and is impaired in patients with spinocerebellar ataxia.

Our cerebellum has been proposed to generate prediction signals that may help us plan and execute our motor programmes. However, to what extent our cerebellum is also actively involved in perceiving the action of others remains to be elucidated. Using functional MRI, we show here that observing goal-directed hand actions of others bilaterally recruits lobules VI, VIIb and VIIIa in the cerebellar hemispheres. Moreover, whereas healthy subjects (n = 31) were found to be able to discriminate subtle differences in the kinematics of observed limb movements of others, patients suffering from spinocerebellar ataxia type 6 (SCA6; n = 21) were severely impaired in performing such tasks. Our data suggest that the human cerebellum is actively involved in perceiving the kinematics of the hand actions of others and that SCA6 patients' deficits include a difficulty in perceiving the actions of other individuals. This finding alerts us to the fact that cerebellar disorders can alter social cognition.