2020 Volume 41 Pages 76-84
It is known that paired associative stimulation （PAS） can induce plastic changes in the central nervous system. The PAS involves the pairing of the electrical single pulse stimulation to a peripheral nerve and single pulse of transcranial magnetic stimulation （TMS） over the primary motor cortex. The purpose of the present study is to investigate the effect of PAS involving transcutaneous spinal cord stimulation （tSCS） and TMS on corticospinal excitability of multiple lower-limb muscles. Ten healthy males participated in the present study. In total, 120 paired stimuli were given to each subject every 9 seconds for 18 minutes. Before and after PAS, corticospinal excitability was evaluated in the rectus femoris （RF）， vastus medialis （VM）， biceps femoris long head （BF）， tibialis anterior （TA）， soleus （SOL）， and medial gastrocnemius （MG） muscles. The results showed that PAS facilitated corticospinal excitability in the BF, SOL, and MG muscles. Furthermore, facilitatory effect of PAS on corticospinal excitability was observed 30 minutes after PAS. These results indicated PAS combining tSCS and TMS could widely induce plastic changes in excitability of the lower-limb motor cortex. However, PAS did not facilitate corticospinal excitability in the RF, VM, and TA muscles. These results also showed a difference in facilitatory effect of PAS on corticospinal excitability among lower-limb muscles, suggesting the existence of a hierarchy of plastic changes in the primary motor cortex. These findings have elucidated the neural mechanism underlying plasticity changes and may provide beneficial information related to motor learning and neurorehabilitation.
