Phase-specific modulation of cortical motor output during movement observation

The effects of different phases of an observed movement on the modulation o f cortical motor output were studied by means of transcranial magnetic stim ulation (TMS). A video-clip of a reaching-grasping action was shown and sin gle TMS pulses were delivered during its passive observation. Times of cort ical stimulation were related to the phases of the shown movement, locking them to the appearance of specific kinematic landmarks. The amplitude of th e motor evoked potentials (MEPs) induced by TMS in the first dorsal interos seus (FDI) muscle was modulated by the amount of the observed finger apertu re. The presence of such an effect is consistent with the notion of a mirro r neuron system in premotor areas that couples action execution and action observation also in terms of temporal coding. NeuroReport 12:1489-1492 (C) 2001 Lippincott Williams & Wilkins.