Effects of Non-invasive Brain Stimulation on Pain Avoidance Behavior in Chronic Pain Patients

Pain avoidance helps with survival. However, chronic pain patients often avoid valued life activities fearing onset or exacerbation of pain. Hence, pain avoidance no longer protects, but reduces quality of life. The goal of this clinical trial is to learn if non-invasive brain stimulation technique called transcranial alternating current stimulation (tACS) impact pain avoidance behavior in chronic pain patients. tACS is a way to gently stimulate the brain using a small, portable device. It sends an extremely weak, continuous alternating current through the scalp. Participants will either get real tACS or a fake (sham) version. Real tACS will stimulate the brain in the alpha frequency (8-12 Hz) which has been found to influence pain avoidance behavior, whereas sham tACS will stimulate the brain in a different frequency that is not known to influence avoidance behavior. The main questions it aims to answer are: Does tACS alter the way chronic pain patients confront pain in terms of avoidance behavior? How does tACS impact brain signals related to pain avoidance behavior? Participants will: 1. fill out self-administered questionnaires asking about their medication use, personality and temperament, mood, including anxiety and depression, current pain level, and any disability you have due to your pain. 2. perform of a pain avoidance task before, during and after 'real' tACS or 'sham' tACS. They may also be asked to stay quiet before, during and after tACS. During this period, we will scan the brain using a neuroimaging device called Magnetoencephalography (MEG). Additionally, Electroencephalography (EEG) brain signals will also be collected using electrodes affixed to the scalp. We may also measure Skin conductance response (SCR) and electrocardiography (EKG) using electrodes affixed to the skin. 3. also get a T1 MRI if they do not have an implanted SCS, DRG, intrathecal pump, or other similar device that are not MRI compatible.

Inclusion Criteria: * Age 18 years or older * Diagnosed with Complex Regional Pain Syndrome (CRPS) Type I or II, based on Budapest criteria * 6 months or more of medically refractory severe pain * Average daily pain for past 30 days \>= 5 on 0-10 scale * Presence of allodynia and/or hyperalgesia * Lower extremity CRPS: bilateral or unilateral pain * Not concurrently treated with neurostimulation therapies such as spinal cord stimulators (SCS) * Absence of co-occurring severe psychiatric disorders (PHQ-9\