Anticipatory postural adjustments (APA) are necessary for counteracting destabilizing forces induced by prime movements. The present study examined APA in a bimanual load-lifting task using simultaneous electroencephalography (EEG) and magnetoencephalography (MEG). A 1-kg weight placed on the left arm was either lifted by an experimenter (imposed condition) or by the subject (voluntary condition). In the imposed condition, inhibition of electromyographic (EMG) activity in the load-bearing muscle (biceps brachii, BB) only occurred after the onset of unloading and was accompanied by event-related desynchronisation (ERD) of cortical activity in the beta frequency band (15-30 Hz). This ERD was localized to the primary sensory cortex using beamforming analyses. In the voluntary condition, EMG inhibition and beta ERD occurred prior to the onset of lifting and beta ERD was localized to the primary motor cortex. This anticipatory cortical and muscle activity ties in well with the feedforward property of APA. This paradigm will be used to study problems of neuro-motor coordination in autism spectrum disorders (ASD).
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