The role of action observation training in motor learning. Behavioral, electromyographic and TMS investigations

The notion that action observation activates the human motor system opened the point of whether it can also promote neuroplasticity processes, in turn facilitating – or even only fastening – the course of neurorehabilitative procedures. The consequent approach, named Action Observation Treatment (AOT), is characterized by three elements: action observation, motor imagery, and action execution repeated over time. Beyond the neurorehabilitative field, AOT represents a promising tool also in the wider context of motor learning, promoting the acquisition and perfectioning of motor competencies throughout all life stages. Starting from these premises, we first investigated whether the regular alternation between action observation and execution is more effective in promoting motor skill learning than training based solely on one of the two elements (motor practice and observational learning), highlighting that the AOT-driven amelioration exceeds even the sum of the other two training. Subsequently, we designed three studies to evaluate the neural correlates of AOT at multiple levels along the neuromuscular chain. An electromyographic investigation demonstrated that the AOT effect reached the peripheral boundaries of the motor system, biasing the muscular pattern of the observer toward that exhibited by the model. A TMS assessment conducted before the training revealed that the AOT outcome is explained by the modulation induced by action observation on corticospinal excitability (CSE) and short intracortical inhibition (sICI). Finally, the CSE facilitation induced by the observation of the to-be-learned task exhibited a decay along the training, whose extent was associated with the performance improvement due to AOT. Taken together, these results not only support the usability of AOT for motor learning but also open the development of individualized training whose efficacy could be early predicted and online monitored, exploiting a battery of neurophysiological and neuropsychological indexes.