Observing and perceiving: a combined approach to induce plasticity in human motor cortex

Objective: To test whether action observation combined with peripheral nerve electrical stimulation was able to evoke plasticity in the primary motor cortex (M1). Methods: The stimulation protocol consisted in the observation of a video showing repetitive thumb-index tapping movements (AO) combined with peripheral electrical nerve stimulation (PNS) delivered on the median nerve (AO-PNS). M1 excitability, measured by means of transcranial magnetic stimulation, was compared with that assessed after AO and PNS alone. Results: M1 excitability increased after AO-PNS, whilst no modifications occurred after AO and PNS alone. The increased M1 excitability after AO-PNS was long-lasting (45 min) and specific for the stimulated muscle. Conclusions: This study described an innovative stimulation paradigm that exploited the mirror neuron system to induce plasticity in M1. However, this occurred only when action observation was combined with afferent signals coming from periphery. Significance: This study supports the literature proposing the mirror neuron system as neural substrate for rehabilitation and opens a debate on the rehabilitative treatments that employ AO to improve patients' motor functions. Indeed, these results suggest that AO has to be combined with afferent inputs from periphery to evoke plasticity in the human motor system. (C) 2014 International Federation of Clinical Neurophysiology.