1-Hz repetitive TMS over ipsilateral motor cortex influences the performance of sequential finger movements of different complexity

To elucidate the role of ipsilateral motor cortex (M1) in the control of unilateral finger movements (UFMs) in humans we used a conditioning protocol of 1-Hz repetitive transcranial magnetic stimulation (1-Hz rTMS) over M1 in 11 right-handed healthy subjects. We analysed the effects of conditioning rTMS on UFMs of different complexity (simple vs sequential finger movements), and performed with a different modality (internally vs externally paced movements). UFMs were monitored with a sensor-engineered glove, and a quantitative evaluation of the following parameters was performed: touch duration (TD); inter-tapping interval (ITI); timing error (TE); and number of errors (NE). 1-Hz rTMS over ipsilateral M1 was able to affect the performance of a sequence of finger opposition movements in a metronome-paced condition, significantly increasing TD and reducing ITI without TE changes. The effects on motor behaviour had a different magnitude as a function of the sequence complexity. Further, we found a different effect of the ipsilateral 1-Hz rTMS on externally paced movements with respect to an internally paced condition. All these findings indicate that ipsilateral M1 plays an important role in the execution of sequential UFMs. Interestingly, NE did not change in any experimental condition, suggesting that ipsilateral M1 influences only the temporal and not the spatial accuracy of UFMs. Finally, the duration (up to 30 min) of 1-Hz rTMS effects on ipsilateral M1 can indicate its direct action on the mechanisms of cortical plasticity, suggesting that rTMS can be used to modulate the communication between the two hemispheres in rehabilitative protocols.