The purpose of this study is to determine whether an investigational drug, called "CDP-Choline", improves memory in people with traumatic brain injury (TBI). To do this, we are asking for people with traumatic brain injury and people without traumatic brain injury to be a part of this study. We will compare results between each group to see if this investigational drug makes a difference with memory. We will also compare brain imaging results and information collected before and after the taking of the study medication to see if there are any differences. We hypothesize that there will be differences in brain activation patterns between individuals with TBI and healthy controls, as well as differences in performance on memory testing at baseline. We further hypothesize that, after treatment with CDP-Choline, the patterns in neuroimaging findings and cognitive testing results for individuals with TBI will more closely resemble results observed for healthy individuals. We hope that what we learn from this study will be helpful in the future treatment of individuals with head injury.