Neurophysiological characterization of transpinal evoked potentials in human leg muscles

Abstract

The objectives of this study were to characterize the neurophysiological properties of the compound muscle action potentials (CMAPs) evoked by transcutaneous electric stimulation of the spine (tsESS), and the effects of tsESS on the soleus H-reflex in seated and standing healthy human subjects. In seated semi-prone subjects with the trunk semi-flexed, two re-usable self-adhering electrodes (cathode), connected to act as one electrode, were placed bilaterally on the iliac crests. A re-usable pregelled electrode (anode) was placed on the thoracolumbar region at thoracic 10-lumbar 1 and held under constant pressure throughout the experiment. CMAPs were recorded bilaterally from ankle muscles with subjects seated semi-prone at 1.0, 0.3, 0.2, 0.125, and 0.1 Hz following tsESS. The soleus H-reflex, evoked by posterior tibial nerve stimulation via conventional methods, was measured following tsESS at inter-stimulus intervals (ISIs) that ranged from -100 to 100 ms with the subjects seated semi-prone and during standing. The tsESS-induced CMAPs were not decreased at low stimulation frequencies, and the soleus H-reflex excitability was profoundly decreased by tsESS at ISIs that ranged from -5 to 20 ms with the subjects seated semi-prone and during standing. CMAPs induced by tsESS may be utilized to assess spinal-to-muscle conduction time while bypassing spinal motoneuron excitability and tsESS can be used as a modality to decrease spinal reflex hyper-excitability in neurological disorders.

Transspinal constant-current long-lasting stimulation: a new method to induce cortical and corticospinal plasticity

“…1C), is apparent in the soleus H reflex and occurs at the Ia afferent-motoneuron synapse because of reduced transmitter release from the previously activated Ia afferents (Pierrot-Deseilligny and Burke 2012). The presence of postactivation TEP depression in this study is opposite to what we have previously observed on a-tsCCS and transcutaneous magnetic stimulation of the spine in semiprone seated subjects (Einhorn et al 2013;Knikou 2013aKnikou , 2013b, suggesting that body position is key to some of the neurophysiological properties of TEPs. However, postactivation TEP depression cannot readily be used to characterize TEPs as monosynaptic reflexes because ␣-motoneurons upon transspinal stimulation are depolarized mostly by transsynaptic actions (see Excitation of Neuronal Elements upon tsCCS).…”

“…TEPs were present at similar latencies in left and right leg muscles, with shorter latencies observed for the RF and MH muscles compared with the more distal ankle flexors/extensors (Table 1), consistent with the TEP latencies we have previously reported (Knikou 2013a(Knikou , 2013b. The latency of TEPs tested in all leg muscles at an interstimulus interval of 5 s did not change before and after c-tsCCS and a-tsCCS (for all TEP latencies before and after P Ͼ 0.05, Table 1).…”

“…We have demonstrated that the transspinal stimulation-induced TEPs in arm and leg muscles are increased when the excitability of peripheral nerves is altered or when descending and ascending inputs are synchronized to meet at the spinal cord (Einhorn et al 2013;Knikou 2013aKnikou , 2013bKnikou , 2014. On the basis of these findings, we hypothesized that transspinal stimulation induces cortical, corticospinal, and spinal neuroplasticity.…”

“…Electrical stimulation delivered epidurally or transcutaneously to the spinal cord generates compound action potentials or transspinal evoked potentials (TEPs) in arm and leg muscles with distinct neurophysiological characteristics (Einhorn et al 2013;Knikou 2013aKnikou , 2013bKnikou , 2014Maruyama et al 1982). TEPs are mediated mostly by direct nonsynaptic activation of motoneurons and indirect transsynaptic excitation of descending projections and local spinal interneuron circuits (Maruyama et al 1982;Sharpe and Jackson 2014).…”

Convergence of flexor reflex and corticospinal inputs on tibialis anterior network in humans

“…TEPs were evoked by transcutaneous stimulation of the thoracolumbar region of the spine according to methods we have previously employed (Knikou, 2013(Knikou, , 2014. Briefly, the cathode monopolar electrode (EP84169, UniPatch, Wabasha, MA) was placed to cover from Thoracic 12 to Lumbar 2 vertebrae levels.…”