The purpose of this research is to study the pain modulation pathways that are thought to be the active in Gulf War Illness veterans with pain symptoms. By studying these pathways, the study aims to find a pain treatment that can improve the pain symptoms of patients diagnosed with GWI and to better understand the mechanism of action of the pain indicators. We intend to achieve this by applying non-invasive transcranial direct current stimulation (tDCS) to patients that will be randomly assigned to active/sham groups and by using behavioral and electrophysiological measures to assess the outcome of the experiments. These measures include a test battery to depict level of pain, electroencephalogram (EEG) and resting state functional magnetic resonance (rsfMRI). We plan to consent and enroll 60 patients that will undergo the entire procedure, which consists of pre-assessments, neurostimulation, post-assessments, and follow up visits at 4 weeks, 12 weeks and 24 weeks.