Effect of observation combined with motor imagery of a skilled hand-motor task on motor cortical excitability: difference between novice and expert.

We examined the effects of observation combined with motor imagery (MI) of a skilled hand-motor task on motor cortex excitability, which was assessed by transcranial magnetic stimulation (TMS). Novices and experts at 3-ball cascade juggling (3BCJ) participated in this study. In one trial, the subjects observed a video clip of 3BCJ while imagining performing it. In addition, the subjects also imagined performing 3BCJ without video clip observation. Motor evoked potentials (MEPs) were recorded from the hand muscles that were activated by the task during each trial. In the novices, the MEP amplitude was significantly increased by video clip observation combined with MI. In contrast, MI without video clip observation significantly increased the MEP amplitude of the experts. These results suggest that action observation of 3BCJ increases the ability of novices to make their MI performing the task. Meanwhile, experts use their own motor program to recall their MI of the task.