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Motor systems

Thumbs up

Motor skills are easily acquired through practise, partially through the acquisition of a motor memory: a change in the cortical movement representation. The results of a new study, published in the Journal of Neuroscience, show that just observing an action can result in the formation of similar motor memories.

When applied over the primary motor cortex, transcranial magnetic stimulation (TMS) can evoke finger and thumb movements. The direction of such TMS-evoked thumb movements can be altered by the prior practise of unidirectional thumb movements: the direction of subsequent evoked thumb movements is changed to align with the direction of the practised movements. This change is thought to reflect a modification of the underlying movement representation in the primary motor cortex.

Katja Stefan and colleagues used the same paradigm to look at how simply observing an action might alter such movement representation. They first established a baseline measure for TMS-evoked activity by applying TMS to the primary motor cortex, which resulted in involuntary thumb movements. Subjects then participated in either a physical training session, in which they practised voluntary thumb movements in a direction opposite to baseline TMS-evoked thumb movements, or they simply observed an actor making the same movements on-screen, without any physical practise. One-third of subjects also saw an actor making similar thumb movements on-screen, but this time in the same direction as the baseline TMS-evoked thumb movements. Finally, TMS-evoked thumb movements were measured again in all subjects and compared with the baseline movements in each individual.

Although the effect was smaller, observing a movement away from the baseline direction resulted in changes in evoked thumb movement similar to those caused by actual physical practise. In both cases, evoked thumb movements changed so that they were more similar to the observed or practised movement. These results suggest that observation alone might result in specific changes in motor representation. The formation of such motor memories may rely on the activity of mirror neurons, which respond both to action execution and observation.

Further studies are required to confirm the role of mirror neurons in the formation of such observation-based motor memories, and to identify the exact location at which these neurons are active. Such observational practise might also prove to be an effective rehabilitative treatment for patients with motor problems who are unable to carry out physical practise.



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Narain, C. Thumbs up. Nat Rev Neurosci 6, 913 (2005).

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