After implantation of SCS trial leads - which is standard of care for evaluating whether SCS improves chronic pain - patients will visit clinic before the trial leads are explanted. During these visits, stimulation will be turned off and the leads will be disconnected from the clinical external pulse generator and reconnected to an external research stimulator. Patients will be seated in a chair and will interface with a touch-screen display where they will participate in a psychophysical task (a two-alternative forced-choice task). More specifically, the task will involve selecting between two options on a screen while spinal stimulation is delivered through the leads. As the patients perform the tasks, audio or video recordings will be made for future research analysis, education, or scientific communication. The research stimulator will also collect epidural signals through the stimulation leads.

The outcome measure will determine the threshold stimulation amplitude in microamperes required to evoke a perceivable sensory percept during spinal stimulation.

The outcome measure will determine the minimum change in stimulation amplitude in microamperes required to evoke a perceivable difference in sensory percepts during spinal stimulation.