Effect of Epidural Stimulation on Muscle Activation and Sensory Perception

Each year, an estimated 34,000 individuals undergo epidural spinal cord stimulation (SCS) surgery to address debilitating chronic low back and leg pain (CLBLP). Although the commercial application of SCS to treat CLBLP was approved by the FDA in 1989, only in the past decade have significant advancements in stimulator technology been introduced. For instance, traditional SCS devices achieved reduction in pain using a type of stimulation known as low-frequency tonic stimulation (LFTS, below 100 Hz), which was dependent on induction of paresthesias (i.e., a tingling sensation) over the areas of pain perception. However, investigators now know that LFTS compromises sensory information flowing back to the spinal cord, which can be important in other spinal cord functions such as proprioception and movement. On the other hand, recent innovations in stimulator technology now provide the capability to apply stimulation frequencies up to 10,000 Hz along with complex waveform patterns - known as high frequency burst stimulation or HFBS - that can mitigate pain perception without the induction of paresthesias and the negative consequences on proprioception and movement. We propose to study the effects of these recently introduced features in SCS technology on motor and sensory spinal thresholds, proprioception and movement in subjects with CLBLP. The spinal cord relies on input from the motor cortex and surrounding extremities to initiate specific muscle recruitment, and recent evidence suggests that preservation of temporally specific proprioceptive information via dorsal column primary afferent fibers is critical for natural motor behaviors such as ambulation. Since the spinal cord is exposed during the placement of the SCS device, information about a subject's motor and sensory spinal pathways can be easily obtained during the regular course of the procedure and compared to proprioceptive and motor responses once the subject is awake and moving with the device turned on. Our lab specializes in electrophysiological recordings in subjects undergoing spinal cord stimulator (SCS) implantation for CLBLP, while MUSC's Locomotion Laboratory specializes in quantifying proprioception and movement in human subjects. In this proposal, investigators will apply these techniques to subjects with CLBLP to determine effects of spinal neuromodulation on motor and sensory thresholds, proprioception, and kinematics.