A fMRI(Functional Magnetic Resonance Imaging) Research Study to Learn More About Multiple Sclerosis and Individuals Potentially Experiencing Memory Difficulties

Inclusion Criteria: * Between 18 and 65 years of age and experiencing some forgetfulness * Diagnosed with MS, currently taking Rebif® and experiencing mild memory problems * Participants will have stable medication dosages 1 month prior to testing * With no past or present neurological disorders (e.g. head trauma, seizures, encephalitis, stroke) except MS * With no known medical illnesses (e.g. diabetes, uncontrolled hypertension, arthritis) * With no psychiatric illness * With no current substance abuse * Females should not be pregnant or nursing * With no metallic devices in the body or claustrophobia Exclusion Criteria: * Previous history of CNS disturbance other than MS * Severe motor or visual impairment that might interfere with the cognitive activation tasks * Prescribed psychoactive medications * Memory deficits caused by other significant neurological disease or psychiatric disorder * Active malignancy within one year of study participation * Known human immunodeficiency virus (HIV) * Current diagnosis of unstable glaucoma; history of myocardial infarction * Symptomatic Coronary Artery Disease within the last 12 months or evidence of ongoing ischemia or uncontrolled atrial or ventricular arrhythmias as shown by ECG; poorly controlled or labile hypertension * History of epilepsy or other seizure disorder within the past 12 months * Allergy or hypersensitivity to amphetamines or other sympathomimetic amines