Chronic pain is a complex neurological disease that adversely impacts function and quality of life. Brain structure and function are altered when an individual is in the chronic pain state. Furthermore, chronic pain is associated with disruptions in functional brain connectivity. Spinal cord stimulation (SCS) is a clinically available non-pharmacological therapy that is used in the management of chronic pain. Although SCS is effective for many, there are individuals who do not benefit. Therefore, in order to better understand brain mechanisms that underlie SCS treatment of chronic pain and to develop brain biomarkers of SCS efficacy, we propose to evaluate functional brain changes in response to SCS. Finding a brain signature of pain relief in response to SCS would improve understanding of how SCS alleviates chronic pain and may help to identify those most likely to respond. The main objective of this study is to assess changes in brain connectivity in response to SCS in individuals with chronic neuropathic pain. We will study two cohorts: Cohort 1 – naive to SCS patients who are undergoing SCS trial period; Cohort 1 – long- term SCS users (≥6 months post implantation). We aim to identify neurophysiological brain signatures of pain relief in these two populations using resting state Near Infrared Spectroscopy and Electroencephalography (rs-fNIRS/EEG). Study Design: We will enroll veterans with refractory chronic neuropathic pain who are currently receiving clinical care within the medical center. Cohort 1: Individuals with chronic neuropathic pain who are naïve to SCS and were selected for SCS trial period as part of their clinical care will participate in two study visits: before the beginning of the SCS trial and the end of the trial period. Data collection will be consistent across all data collection timepoints (T1 – T3) and include rs- fNIRS/EEG and clinical pain measures. Cohort 2: Participants with effective implanted SCS ≥ 6 months will participate in three study visits conducted 24-48 hours apart. Data will be collected during SCS use and following an SCS washout period. Data collection will be consistent across all data collection timepoints(T1-T4) and include rs-fNIRS/EEG and clinical pain measures. Both cohorts will receive paresthesia based SCS. AIM 1 is to characterize neurophysiological (rs-fNIRS/EEG) brain signature of pain relief during the SCS trial period for patients with chronic neuropathic pain who are naïve to SCS. AIM 2 is to characterize neurophysiological (rs-fNIRS/EEG) brain signature of pain relief in patients with chronic neuropathic pain who have utilized SCS for ≥6 months. Outcome Measures to address both aims include rs-functional connectivity (rs-fNIRS/EEG); and a composite clinical pain assessment that will include Numeric Pain Rating Scale (NPRS), Patient Reported Outcomes Measurement Information System-29 profile v2.1(PROMIS-29); EQ-5D-5L; Patient Global Impression of Change (PGIC); painDetect; and activity mon...