Short-term upper limb disuse can induce plastic modifications in the contralateral and ipsilateral primary motor cortices (M1s) resulting in an hemispheric unbalance. However, it is still unclear whether these observed neuroplastic changes during arm immobilization are mainly attributable to the absence of voluntary movements or to the reduction of proprioceptive information or, more likely, to the combination of both. Therefore, the goal of this work was to investigate the role of proprioception in modulating M1s excitability and hemispheric balance during a short-term period of upper limb immobilization.

We evaluated both the excitability of the two M1s and the interhemispheric inhibition (IHI) in two groups of healthy subjects whose right arm was immobilized. Further, in one group of the two, a muscle vibration protocol was administered to the flexor digitorum interosseus muscle of the right hand during the immobilization period in order to reproduce a series of proprioceptive inputs.

We found that the muscle vibration of the right immobilized arm was able to cope with neuroplastic changes induced by immobilization i) reducing the inhibitory effect on left M1 excitability; ii) re-establishing the correct transcallosal control from left to right M1; iii) preventing the excitability increase of the corticospinal and transcallosal neurons of right M1due to left arm overuse.

Our findings suggest that proprioception plays an important role in modulating cortical plasticity.