Conditioning effect of peroneal nerve stimulation on the transcutaneously elicited posterior root-muscle reflex

Abstract

The effects of locomotor training and spinal cord stimulation depend on the central excitability of the networks below the injury. Stimulation of the peripheral nerve allows targeting these networks to alter their excitability. We tested the effects of trains of peroneal nerve stimulation. The modifications of monosynaptically evoked lumbosacral motoneuron responses were tested by non-invasive elicitation of posterior root-muscle (PRM) reflexes simultaneously in multiple lower limb muscle groups. We conducted our measurements on five subjects with intact nervous systems . One-second conditioning trains of peroneal nerve stimulation with a frequency of 15, 30 and 50 Hz were applied at 0.8, 1.2 and 1.5 times the motor threshold. Following 20, 50, 100, 200, 500 and 1000 ms inter-stimulus-intervals, test PRM reflexes were elicited through surface el ectrodes over T11 -T12 vertebrae. In above -threshold stimulation a general suppression of ipsilateral reflex responses , that increased with increasing conditioning frequency and intensity and lasted at least one second , were observed . This suppression was more prominent in the distal than in the proximal muscle groups. No conclusive statement can be made regarding the contralateral leg, where both excitatory and inhibitory tendencies were observed. Peripheral stimulation has an effect on all lumbar segments of the spinal cord, beyond the segments that are stimulated, which can be beneficial for rehabilitation after spinal cord injury (SCI), where the goal is to affect the excitability of the networks below the injury. While we studied only the effects on healthy subjec ts , they should be further studied in SCI individuals , and additional tests on the altere d central state of excitability in SCI should be conducted .