Physicians at the Partners MS Center and the Brigham and Women's Hospital (BWH) Behavioral Neurology clinic may present the study to a subject during a regular scheduled clinic visit. If the subject is interested in the study, a copy of the consent form will be given. At the time of the subject's initial screening visit, a licensed physician investigator will answer any questions the subject may have regarding the study and subsequently obtain informed consent. In accordance with NIH guidelines, efforts will be made to attain a mix of study participants, in terms of gender and racial/ethnic representation.