Paired corticospinal-motoneuronal stimulation modulates motor learning associated with ballistic finger movement

Abstract Introduction: Paired corticospinal-motoneuronal stimulation (PCMS), which combines peripheral nerve electrical stimulation (PNS) with transcranial magnetic stimulation (TMS) over the contralateral primary motor cortex, induces plasticity at synapses between the corticospinal tract and spinal motoneurons. We investigated effects of spinal synaptic plasticity induced by PCMS on ballistic finger movements. Methods: Eleven right-handed healthy volunteers participated in this study. The subject performed his two sets of 120 ballistic abductions movements of the right index finger immediately after the beep and the finger movement acceleration was recorded. Subjects received online visual feedback of the acceleration during the task and were continuously encouraged by the experimenter to increase acceleration throughout the training. We explored the effects of three different PCMS protocols on the subsequent learning of ballistic finger movement. In LTP-like plasticity induction protocol by PCMS, two stimuli were given so that antidromic input from PNS and orthodromic volleys from TMS arrive at motoneurons simultaneously. In LTD-like plasticity induction protocol, two stimuli were set so that orthodromic volleys by TMS reach 9ms before the arrival of antidromic input from PNS. Sham stimulation protocol was also performed. Finger movement acceleration and cervicomedullary motor-evoked potential amplitudes (CMEPs) were recorded before and after PCMS to investigate their changes after the interventions. Results: PCMS for LTP increased CMEPs and finger movement acceleration, while PCMS for LTD decreased CMEPs and finger movement acceleration. Neither CMEPs nor acceleration was affected by sham stimulation. Regression analyses demonstrated a significant positive correlation between PCMS-induced CMEP changes and PCMS-induced finger movement acceleration. Conclusions: Motor learning can be modulated bidirectionally by PCMS, which induces plasticity at synapses between the corticospinal tract and spinal motoneurons. The present findings suggest the possibility to use PCMS as a treatment for motor recovery in patients with spinal cord injury or neurological diseases. Research Category and Technology and Methods Basic Research: 10. Transcranial Magnetic Stimulation (TMS) Keywords: Paired corticospinal-motoneuronal stimulation (PCMS), motor learning, finger movement acceleration, cervicomedullary motor-evoked potential amplitudes (CMEPs)