Post traumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) frequently co-occur, and these patients often have disrupted sleep. Poor sleep quality is associated with several poor heath outcomes that overlap with those that are experienced in PTSD. These can include poor cognitive performance and difficulty with emotional regulation. Effective treatment of sleep problems in these individuals could substantially improve these symptoms and quality of life. Transcutaneous vagal nerve stimulation (tVNS) is a non-invasive electrical stimulation technique that has been previously shown to moderate the response of the sympathetic nervous system and reduce hyperarousal in patients with mTBI and PTSD. In this study, our objective is to determine the effect of tVNS in changing sleep architecture and subjective sleep quality, as well as changing emotional and cognitive performance.