Effects of paired stimulation with specific waveforms on cortical and spinal plasticity in subjects with a chronic spinal cord injury

Abstract

Paired stimulation can cause neuroplasticity in corticospinal and spinal pathways in subjects with a chronic spinal cord injury (SCI). We aimed to know the effects of different waveforms using paired stimulations with bicycling in subjects with a chronic SCI. Recruited subjects with an SCI underwent three treatment interventions in random order for 4-20 min followed by 30 min of bicycling (control, repetitive transcranial magnetic stimulation (TMS; rTMS) at 20 Hz with transspinal direct current stimulation (tsDCS), and intermittent theta burst stimulation (iTBS) with tsDCS with a 1-week gap period. A TMS method was employed to record the resting motor threshold (RMT), the 90% values of which was used as the stimulation intensity, and the Hoffman (H)-reflex was measured by stimulating the tibial nerve in the popliteal fossa. The RMT, motor evoked potential (MEP) latency, MEP peak-to-peak amplitude, and H-reflex latency as primary variables and lower extremity motor scale (LEMS) and modified Ashworth spasticity scale (MAS) as secondary variables were analyzed before and after the interventions. The MEP latency, MEP amplitude, and LEMS significantly improved with the rTMS-iTBS/tsDCS or the rTMS-20 Hz/tsDCS (p < 0.050) protocols compared to the control intervention. All other outcome measures, including RMT, H-reflex latency, and MAS score showed some changes but did not fully attain a level of significance. The paired stimulation with rTMS-iTBS/tsDCS was equally effective to produce neuroplastic effect in subjects with chronic SCI compared to the conventional TMS-20 Hz/tsDCS intervention.