Cervical intraspinal microstimulation evokes robust forelimb movements before and after injury

Abstract

Objective Intraspinal microstimulation (ISMS) is a promising method for reanimating paralyzed limbs following neurological injury. ISMS within the cervical and lumbar spinal cord is capable of evoking a variety of highly-functional movements prior to injury, but the ability of ISMS to evoke forelimb movements after cervical spinal cord injury is unknown. Here we examine the forelimb movements and muscles activated by cervical ISMS both before and after contusion injury. Approach We documented the forelimb muscles activated and movements evoked via systematic stimulation of the rodent cervical spinal cord both before injury and three, six and nine weeks following a moderate C4/C5 lateralized contusion injury. Animals were anesthetized with isoflurane to permit construction of somatotopic maps of evoked movements, and quantify evoked muscle synergies between cervical segments C3 and T1. Main results When ISMS was delivered to the cervical spinal cord, a variety of responses were observed at 68% of locations tested, with a spatial distribution that generally corresponded to the location of motor neuron pools. Stimulus currents required to achieve movement and the number of sites where movements could be evoked were unchanged by spinal cord injury. A transient shift toward extension-dominated movements and restricted muscle synergies were observed at three and six weeks following injury, respectively. By nine weeks after injury, however, ISMS-evoked patterns were similar to spinally-intact animals. Significance The results demonstrate the potential for cervical ISMS to reanimate hand and arm function following spinal cord injury. Robust forelimb movements can be evoked both before and during the chronic stages of recovery from a clinically-relevant and sustained cervical contusion injury.

Evaluation of optimal electrode configurations for epidural spinal cord stimulation in cervical spinal cord injured rats

“…Currently, data on the effects of epidural stimulation to neuromodulate the cervical cord chronically are non-existent. Previous work in the rats has shown that instraspinal stimulation of the cervical segments of the spinal cord in rats elicits motor responses in multiple forelimb muscles (Sunshine et al, 2013) and selected stimulation parameters can facilitate functional reaching and grasping movements in monkeys (Zimmermann et al, 2011; Sharpe and Jackson, 2014). Chronic intraspinal stimulation of the spinal cord has been reported to improve forelimb function in SCI rats (Kasten et al, 2013; Mondello et al, 2014).…”

Electrical neuromodulation of the cervical spinal cord facilitates forelimb skilled function recovery in spinal cord injured rats

“…Previous work has shown that intraspinal stimulation at the cervical segments of the spinal cord elicits motor responses in multiple forelimb muscles in rats (Sunshine et al, 2013) and that selected stimulation parameters can facilitate functional reaching and grasping movements in non-injured monkeys (Zimmermann et al, 2011; Sharpe and Jackson, 2014). It also has been shown that chronic intraspinal stimulation at the cervical spinal cord can improve forelimb function in rats with a cervical SCI (Kasten et al, 2013; Mondello et al, 2014).…”

Increased antagonist muscle activity in cervical SCI patients suggests altered reciprocal inhibition during elbow contractions

“…A cSCI between C5 and C7 leads to minimal loss of control of the elbow flexors, but to disrupted voluntary control of the elbow extensors (Maynard et al, 1997;Sunshine et al, 2013), which give a unique opportunity to investigate changes in the activation of agonist and antagonist muscles Wiegner, 1992, 1996). Given that the signals from peripheral afferents and descending pathways may considerably differ between cSCI and healthy participants during actual contractions (Boorman et al, 1996), comparisons at both similar percentages of the maximal net torque and absolute net torques allow an evaluation of the mechanisms underlying the performance, as opposed to performance itself.…”