Associative cortico-cortical plasticity may affect ipsilateral finger opposition movements.

We have recently demonstrated that cortico-cortical paired associative stimulation (cc-PAS) can modulate interhemispheric inhibition (IHI) in the human brain. Here we further explored the after effects of cc-PAS on fine hand movements. Ten healthy right-handed volunteers received 90 paired transcranial stimuli to the right and left primary motor hand area (M1(HAND)) at an interstimulus interval (ISI) of 8 ms. We studied the after effects of cc-PAS on the performance of repetitive finger opposition movements of different complexity on both hands using a sensor-engineered glove. A quantitative evaluation of the following parameters was performed: Touch Duration (TD), Inter Tapping Interval (ITI) and Number of Errors (NE). We confirmed previous data by showing that left-to-right and right-to-left cc-PAS attenuated IHI. The new finding is that both left-to-right and right-to-left cc-PAS were able to influence the performance of a simple finger opposition movement changing the duration of TD and ITI. Interestingly the effect on the two hands was opposite in direction. These results provide further insight that cc-PAS can induce associative plasticity in connections between the targeted cortical areas influencing motor hand performances. These results may be relevant for future rehabilitative applications.