The role of ipsilateral primary motor cortex (ipsi-M1) in the process of motor learning is still under debate. Neuroimaging experiments suggest activation in the ipsilateral central brain region in the late phase of motor sequence learning, after subjects have known the sequence order completely. Here, we tested the hypothesis that ipsi-M1 activation could be the result of an increased connectivity between right posterior parietal cortex (rPPC) to the ipsi-M1 in order to encode visuo-spatial information.

19 subjects executed a learning task with an engineered glove with the right hand. We measured reaction time (RT) and Touch Duration (TD) thus providing a description of the motor behaviour. In 10 subjects we measured motor evoked potentials recruitment curve with transcranial magnetic stimulation (TMS) in right M1 while in the remaining 9 we studied connectivity between rPPC area and right M1 by means of a paired pulse TMS paradigm. All TMS procedures were performed before and after the learning task. Sequence learning induced a significant decrease of RT and a change of motor strategy (increased TD). Subjects showed, at the end of the task, a significant increase of cortical excitability in the ipsi-M1 and stronger facilitatory interaction between rPPC area and right M1.

Cortical excitability results support the hypothesis that explicit sequence learning accompanies changes in ispilateral hemisphere, likely due to the engagement of rPPC in learning process.