Spinal segment-specific transcutaneous stimulation differentially shapes activation pattern among motor pools in humans

Abstract

Transcutaneous and epidural electrical spinal cord stimulation techniques are becoming more valuable as electrophysiological and clinical tools. Recently, we observed selective activation of proximal and distal motor pools during epidural spinal stimulation. In the present study, we hypothesized that the characteristics of recruitment curves obtained from leg muscles will reflect a relative preferential activation of proximal and distal motor pools based on their arrangement along the lumbosacral enlargement. The purpose was to describe the electrophysiological responses to transcutaneous stimulation in leg muscles innervated by motoneurons from different segmental levels. Stimulation delivered along the rostrocaudal axis of the lumbosacral enlargement in the supine position resulted in a selective topographical recruitment of proximal and distal leg muscles, as described by threshold intensity, slope of the recruitment curves, and plateau point intensity and magnitude. Relatively selective recruitment of proximal and distal motor pools can be titrated by optimizing the site and intensity level of stimulation to excite a given combination of motor pools. The slope of the recruitment of particular muscles allows characterization of the properties of afferents projecting to specific motoneuron pools, as well as to the type and size of the motoneurons. The location and intensity of transcutaneous spinal electrical stimulation are critical to target particular neural structures across different motor pools in investigation of specific neuromodulatory effects. Finally, the asymmetry in bilateral evoked potentials is inevitable and can be attributed to both anatomical and functional peculiarities of individual muscles or muscle groups.

Effects of paired transcutaneous electrical stimulation delivered at single and dual sites over lumbosacral spinal cord

“…Participants provided written informed consent to the experimental procedures, which were approved by the local institutional review board. Detailed description of the transcutaneous electrical spinal cord stimulation protocol has been reported [25]. During the experiment, the participants stayed relaxed in a supine position.…”

“…We recently demonstrated that transcutaneous electrical spinal cord stimulation can be used to differentially activate dorsal roots and corresponding motor pools based on their anatomical arrangements along the rostro-caudal axis of the lumbosacral enlargement [25]. In light of the spatial arrangement of the motor pools and networks along the lumbosacral enlargement (Fig.…”

Transcutaneous electrical spinal-cord stimulation in humans

“…We have characterized the relative selectivity of recruitment of different motor pools innervating leg muscles in non-injured subjects by using transcutaneous stimulation along the rostro-caudal axis of the lumbosacral enlargement (Fig. 3), at sites similar to a previous study with epidurally implanted electrodes [16]. Variation in many characteristics of the evoked potentials reflects a relative preferential activation of proximal and distal leg muscles based on the rostro-caudal position of the sensory-motor pathways and motor neuron pools.…”

Combination of Functional Electrical Stimulation and Noninvasive Spinal Cord Electrical Stimulation for Movement Rehabilitation of the Children with Cerebral Palsy

“…TSCS at T11 and L1 vertebral levels of proximal and distal motor pools in paralyzed subjects are facilitated [24]. This effect is evident in spinal motor evoked potentials of proximal and distal leg muscles to single stimulation pulses [23]. We have found that epidural SCS combined with training can increase hand grip force in spinal patients with cervical injuries [18].…”

“…Center of pressure stabilization and decrease of the pathological body forward inclination were observed. The effect may be connected with the activation of motor pools of muscles involved in maintaining the upright by TSCS [23]. Another reason --increase of strength of many muscles by FES and by this body weight support in upright posture was facilitated [8].…”