Abstract
BackgroundA complete spinal cord transection results in loss of all supraspinal motor control below the level of the injury. The neural circuitry in the lumbosacral spinal cord, however, can generate locomotor patterns in the hindlimbs of rats and cats with the aid of motor training, epidural stimulation and/or administration of monoaminergic agonists. We hypothesized that there are patterns of EMG signals from the forelimbs during quadrupedal locomotion that uniquely represent a signal for the “intent” to step with the hindlimbs. These observations led us to determine whether this type of “indirect” volitional control of stepping can be achieved after a complete spinal cord injury. The objective of this study was to develop an electronic bridge across the lesion of the spinal cord to facilitate hindlimb stepping after a complete mid-thoracic spinal cord injury in adult rats.MethodsWe developed an electronic spinal bridge that can detect specific patterns of EMG activity from the forelimb muscles to initiate electrical-enabling motor control (eEmc) of the lumbosacral spinal cord to enable quadrupedal stepping after a complete spinal cord transection in rats. A moving window detection algorithm was implemented in a small microprocessor to detect biceps brachii EMG activity bilaterally that then was used to initiate and terminate epidural stimulation in the lumbosacral spinal cord. We found dominant frequencies of 180–220 Hz in the EMG of the forelimb muscles during active periods, whereas these frequencies were between 0–10 Hz when the muscles were inactive.Results and conclusionsOnce the algorithm was validated to represent kinematically appropriate quadrupedal stepping, we observed that the algorithm could reliably detect, initiate, and facilitate stepping under different pharmacological conditions and at various treadmill speeds.
Highlights
A complete spinal cord transection results in loss of all supraspinal motor control below the level of the injury
Phase I: prior to the first manual pulse and with the treadmill turned off, there is some random motion in the forelimbs that is not detected by the electronic bridge as stepping
Phase III: the treadmill is moving at the same speed and the EMG from the forelimb muscles continues to be detected. electrical-enabling motor control (eEmc) results in oscillatory weight-bearing movements in the hindlimbs
Summary
A complete spinal cord transection results in loss of all supraspinal motor control below the level of the injury. Pharmacologically enabling motor control strategies (fEmc) using serotonergic agonists of 5-HT1A,2A and 5-HT7 receptors in combination with epidural stimulation, i.e., electrical-enabling motor control (eEmc) [8,9,10], have been used to recover considerable function after paralysis. These two interventions combined with the availability of sensory information in real time have been used to induce full weight-bearing stepping in complete spinal rats [10,11]. The spinal rats did not step when the treadmill was turned on but no eEmc was provided, indicating that the stimulation was necessary for the spinal rats to step
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