Sensory Responses to Dorsal Root Stimulation

The goal of this project is to characterize the types of sensations that can be evoked via electrical stimulation of the spinal cord and spinal nerves. Patients will be recruited from a local pain clinic, each with a spinal cord stimulation device implanted, to participate in experiments to explore the ability to modulate and control the modality, intensity, focality, and location of the sensations evoked by stimulation through the spinal cord stimulator leads. Investigators will connect spinal cord stimulator leads to a custom stimulator system and will ask subjects to report the types of sensations felt. Invesigators will also perform detailed psychophysical metrics to examine participants' ability to discriminate sensations.

For this study, investigators aim to determine whether DRG and spinal root stimulation might be viable techniques for restoring feedback. Investigators will focus on patients undergoing temporary percutaneous trials of DRG or lateral spinal cord stimulation with leads manufactured by either Boston Scientific (under PMA P030017) or St. Jude (under PMA P150004), which have FDA premarket approval for the management of chronic pain in the trunk and lower limbs. In this early experiment, investigators will not focus on individuals with limb loss, but rather will include patients already undergoing a percutaneous trial of DRG or spinal root stimulation to treat pain. Investigators will characterize the location, modality, and intensity of sensations evoked in the hands or feet with stimulation delivered by an external stimulator.

During psychophysical stimulation trials, an external stimulator will be connected to the SCS lead, a volley of stimulation will be performed, and the subject will be asked to respond to standard psychophysical questions, as well as to provide any additional comments.

These systems are indicated as an aid in the management of chronic intractable pain of the trunk and/or limbs, including unilateral or bilateral pain associated with the following: failed back surgery syndrome, intractable low back pain and leg pain. Stimulation will be applied to the system using an external stimulator to see if sensations can be evoked in the participant's limb/foot.

Quantify the threshold stimulus required to evoke sensory percepts during epidural spinal nerve stimulation.

Quantify the threshold stimulus required to evoke neurophysiological responses during epidural spinal nerve stimulation

Document the subjective perception of lumbosacral epidural spinal nerve stimulation for restoration of sensation. The investigators will ask each subject to provide subjective feedback on their perceived utility of the sensory feedback provided by the device.

Inclusion Criteria: Subjects must be between the ages of 18 and 70 years old. Subjects must be undergoing an epidural spinal cord implanted electrode array clinical trial with Dr. Helm for the management of pain. Persons must understand the consent and the procedures. Exclusion Criteria: Persons with open wounds; Persons with implanted metal rods in the spine or limbs; Persons with defibrillator or pacemaker; Persons with permanent skin metal tags or decorations.