Primary motor cortex and cerebellum are coupled with the kinematics of observed hand movements.

To find out in which detail the kinematics of observed movements is represented in the viewer's brain, we searched for brain areas displaying coherent magnetoencephalographic (MEG) activity with observed repetitive hand movements. Whole-scalp MEG signals were recorded from 10 right-handed young adults who observed repetitive 3-Hz right-hand flexion-extension movements performed by the experimenter. The coherence between the subject's MEG signals and the experimenter's index-finger acceleration was computed to index the level of actor-observer coupling. The underlying cortical activity was identified with Dynamic Imaging of Coherent Sources. In all subjects, coherence spectra showed statistically significant peaks at movement frequency (F0) and its first harmonic (F1), strongest at visual areas. At F0, additional significant local coherence maxima, clearly distinct from the coherent visual areas, occurred in the primary motor (M1) cortices of both hemispheres and in the cerebellum (posterior vermis and hemispheres). Our results highlight the time-sensitive involvement of the M1 cortices and cerebellum in the kinematic representation of observed repetitive, non-goal directed motor actions.