Stronger reactivity of the human primary motor cortex during observation of live rather than video motor acts

The monkey premotor cortex contains neurons that are activated both when the monkey performs motor acts and when he observes actions made by others. A similar mirror neuron system, involving several brain areas, has been found in humans. We recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects when they observed live and videotaped finger movements. The left and right median nerves were stimulated alternatingly and the poststimulus level of the similar to 20Hz rhythm was quantified. Compared with the rest condition, the similar to 20Hz rhythm was dampened 15-19% more when the subjects observed live rather than videotaped hand movements, indicating stronger activation of the primary motor cortex. These results suggest that the human mirror neuron system differentiates natural and artificially presented movements. (C) 2001 Lippincott Williams & Wilkins.