The proposed study will evaluate a new approach to cognitive rehabilitation of mTBI using a brain stimulation technique called Remotely Supervised Transcranial Direct Current Stimulation combined with Cognitive Training (RS-tDCS+) which has shown promise for improving complex attention in both healthy and clinical populations. RS-tDCS+ is a home-based, low-risk, non-invasive technique that is designed to boost cognitive training by enhancing learning and the brain's ability to reorganize connections. This study will evaluate RS-tDCS+ for improving complex attention in Active Duty Service Members (ADSM) and Veterans with a history of mTBI. Different tests of complex attention and symptom questionnaires will be used to determine the effects of real versus sham (placebo) RS-tDCS+. Second, the investigators will investigate electrical and connectivity changes in the brain associated with RS-tDCS+ using electroencephalogram (EEG) and magnetic resonance imaging (MRI). Third, the investigators will investigate the lasting effects of any observed changes by evaluating participants at 1 and 6 weeks post-treatment. Lastly, the investigators will explore the impact of individual differences (e.g., PTSD, depression, sleep quality, time since injury, baseline impairment, age, sex, ADSM versus Veteran) on treatment outcome.