Up to 65% of patients with multiple sclerosis (MS) experience cognitive dysfunction. Diminution of mental capacity has a pervasive and profound impact on their quality of life. Subtle changes in white matter predict cognitive changes in these patients but how this disrupts brain function remains unclear. Development of effective therapeutics to restore normal cognition hinges on elucidating these functional changes. The investigators seek to uncover the patho-physiological basis for cognitive decline in MS. The investigators hypothesize that cognitive decline originates from disrupted gamma oscillations and that gamma oscillations are disrupted by molecular changes triggered by demyelination.

Inclusion Criteria (*applicable to controls):

1. Must be between 6 and 17 years and 11 months of age*;
2. Have a diagnosis of MS according to the revised McDonald diagnostic criteria and/or International Pediatric MS Study Group criteria;
3. Has English language knowledge at the level needed to complete clinical questionnaires (4th grade level).*

Exclusion Criteria (*applicable to controls):

1. Neurological comorbidity.*;
2. Relapses or requires treatment with steroids within 30 days from enrollment;
3. Is pregnant at the time of enrollment.*;
4. Has any metal parts in their body (i.e. Cochlear (ear) implant, metal braces (dental fillings are o.k.).*;
5. Is younger than 6 years of age.*;
6. Is older than 18 years of age.*;
7. Has prior history of traumatic brain injury, neurological disorder, cerebral palsy, developmental delay or learning disability.*;
8. Requires sedation for brain scanning.*;
9. Is claustrophobic, as brain scanning requires children to enter a tunnel in the MRI machine.*

Seven patients who have pediatric-onset multiple sclerosis and 7 healthy (non-patient) children are expected to participate in this study.