Recruitment of upper-limb motoneurons with epidural electrical stimulation of the cervical spinal cord

Abstract

Epidural electrical stimulation (EES) of lumbosacral sensorimotor circuits improves leg motor control in animals and humans with spinal cord injury (SCI). Upper-limb motor control involves similar circuits, located in the cervical spinal cord, suggesting that EES could also improve arm and hand movements after quadriplegia. However, the ability of cervical EES to selectively modulate specific upper-limb motor nuclei remains unclear. Here, we combined a computational model of the cervical spinal cord with experiments in macaque monkeys to explore the mechanisms of upper-limb motoneuron recruitment with EES and characterize the selectivity of cervical interfaces. We show that lateral electrodes produce a segmental recruitment of arm motoneurons mediated by the direct activation of sensory afferents, and that muscle responses to EES are modulated during movement. Intraoperative recordings suggested similar properties in humans at rest. These modelling and experimental results can be applied for the development of neurotechnologies designed for the improvement of arm and hand control in humans with quadriplegia.

Brain-Computer-Spinal Interface Restores Upper Limb Function After Spinal Cord Injury

“…Using epidural stimulation to increase the variety of forelimb movements may require a wider implant with a larger number of channels to cover multiple spinal segments and dorsal root entry zones [50]. This requires advancements in electrode technology that are already underway [51] and also an increased physiological understanding of spinal stimulation [52,53].…”

Low-Intensity and Short-Duration Continuous Cervical Transcutaneous Spinal Cord Stimulation Intervention Does Not Prime the Corticospinal and Spinal Reflex Pathways in Able-Bodied Subjects

“…Consistent with epidural SCS approaches, noninvasive transcutaneous spinal cord stimulation (tSCS) has also been utilized successfully in applications for improving sensory and motor function during lower-limb voluntary movement [6] and walking using lumbar stimulation [7][8][9][10][11][12], trunk stability and standing with lower thoracic and lumbar stimulation [13,14], and gripping and upper-limb function with cervical stimulation [15][16][17][18][19]. Computer simulations and experimental studies using animal models as well as human studies have shown compelling evidence that electric impulses induced by either implanted epidural or surface non-invasive electrodes can primarily activate the afferent fibers in the posterior roots of the spinal cord [20][21][22][23][24][25]. Since the stimulated afferent fibers activated by tSCS have synaptic connections to the spinal interneurons and motoneurons, tSCS application can therefore be utilized to modulate spinal motor excitability.…”

A modular strategy for next-generation upper-limb sensory-motor neuroprostheses

“…88 Alternatively, upper-limb movement restoration is obtained by stimulating the spinal cord via the ''e-dura,'' a soft electrode that exploits computational models with a closedloop controller module. 91,92 This approach argues that spared spinal circuits can generate skilled hand movements. [93][94][95] Hence, the idea of activating spinal circuits, rather than muscles, is grounded on the hope that low-level control policies can be delegated to existing circuits that have evolved to perform the desired movement.…”