Differential motor cortex excitability during observation of normal and abnormal goal-directed movement patterns

Beta (∼20-Hz) activity induced by median nerve stimulation has been reported to be located in the primary motor cortex (M1) and associated with various movement-related tasks. It has been evident that the ∼20-Hz activity was suppressed more in the observation of goal-directed than non-goal-directed tool use. However, it remains unclear whether this rhythmic activity is further modulated by the observation of normal and abnormal goal-directed hand movements. We recorded neuromagnetic responses in 19 right-handed healthy adults while they kept relaxed (Rest), manipulated a small cube (Act), observed videotapes with normal (Normal) or abnormal (Abnormal) hand actions. The M1 ∼20-Hz rebound powers were quantified through minimum norm estimate and time-frequency analysis at the source level. The results showed that compared to the Rest condition, the M1 ∼20-Hz activities were significantly decreased when subjects observed normal and abnormal hand actions. The suppression was more profound in the Normal than Abnormal condition, indicating a stronger M1 activation during observing graceful, undistorted movement patterns. Our data provided a neurophysiological basis to differentiate the motor cortical activities in the observation of normal and abnormal hand actions. Further research is warranted to verify its clinical benefits in patients with stroke.