 This is a pilot study. The objective is to further understand the mechanism by which amantadine improves function in patients with persistent vegetative state and minimally conscious state. Specifically, the investigators will measure the size of the nerve fibers that mediate arousal reticular activating system, or RAS pre and post treatment on MRI tractography. MRI findings will be correlated with the Disability Rating Scale DRS score. The information gathered from this study will be used to formulate a larger clinical trial. 