Modulation of neuromagnetic oscillatory activity during the observation of oro-facial movements.

A number of MEG/EEG studies have shown modulation of endogenous sensorimotor (mu and beta) rhythms during the observation of hand movements. These modulations are similar to patterns that occur during execution of movement and it has been hypothesised that the neural substrates of these rhythms may play a role in action representation and understanding the actions of others. In this experiment we wished to determine whether similar responses would be obtained during the observation of oro-facial movements. Neuromagnetic recordings (151 channels, CTF Systems) were obtained from six healthy subjects while they (1) observed a video of an experimenter making oro-facial movements (2) imitated the same movements and (3) observed hand movements. Source scanning using synthetic aperture magnetometry (SAM) was used to find changes in source power between these active conditions compared to pre-stimulus control conditions where no movement occurred. SAM images were created with 5 mm resolution in the beta (15-35 Hz) and mu (8-15 Hz) bands and showed source power decreases over parietal, occipital and sensorimotor areas. Time-frequency analysis of virtual SAM sensors from sensorimotor areas showed event-related desynchronisation of mu and beta bands following the onset of movement in all three conditions. These data demonstrate comparable activations of visuomotor mechanisms during observation or imitation of mouth movements and during observation of hand movements. These results support the notion that sensorimotor mechanisms play a role in achieving a representation of the oro-facial gestures of others.