Assessment of tDCS-Induced Neuronal Responses in Multiple Sclerosis (MS) With Advanced MRI

Inclusion Criteria for MS Patients: * Participants must be 18 years of age or older * Standardized SDMT Z-score \> - 3.0 * Fatigue Severity Scale score \> 36 * Definite MS diagnosis as assessed by licensed physician any subtype including Relapsing Remitting (RRMS), Primary Progressive (PPMS) or Secondary Progressive (SPMS) * Score of ≤ 7.0 on the Expanded Disability Status Scale * Clinically stable without disease progression in the past 3 months * Has stable and continuous access to internet service at home compatible with the study laptop (Wi-Fi or Ethernet cable) * Adequate internet capacity for remote monitoring, as tested by http://www.speedtest.net/ * Adequate home facilities (enough space, access to quiet and distraction free area) * Able to commit to the four-week period of training sessions with baseline and two follow-up visits Exclusion Criteria for MS Patients: * Extreme claustrophobia * Relapse or steroid use in previous month * History of mental retardation, pervasive developmental disorder, or other neurological condition associated with cognitive impairment * Primary psychiatric disorder that would influence ability to participate * Current uncontrolled seizure disorder * Current substance abuse disorder * Any skin disorder/sensitive skin (e.g., eczema, severe rashes), blisters, open wounds, burn including sunburns, cuts or irritation, or other skin defects which compromise the integrity of the skin at or near stimulation locations (where electrodes are placed) * Treatment for a communicable skin disorder currently or over the past 12 months * Have any irremovable piercings, MRI-contraindicated implantations or metallic based-tattoos * Pregnant or breastfeeding * Wide Range Achievement Test-4th Edition (WRAT-4) Reading Recognition Scaled Score \< 85 * Beck Depression Inventory - Fast Screen (BDI-FS) score \> 9 Inclusion Criteria for Healthy Controls: * Participants must be 18 years of age or older * Standardized SDMT Z-score \> - 3.0 * Have not been diagnosed with MS or other neurological disorder * Adequate internet capacity for remote monitoring, as tested by http://www.speedtest.net/ (HC subgroup only) * Adequate home facilities including enough space, access to quiet and distraction free area (HC subgroup only) * Able to commit to the four-week period of training sessions with baseline and one follow-up visit (HC subgroup only) Exclusion Criteria for Healthy Controls: * Extreme claustrophobia * History of mental retardation, pervasive developmental disorder or other neurological condition associated with cognitive impairment * Primary psychiatric disorder that would influence ability to participate * Current uncontrolled seizure disorder * Current substance abuse disorder * Any skin disorder/sensitive skin (e.g., eczema, severe rashes), blisters, open wounds, burn including sunburns, cuts or irritation, or other skin defects which compromise the integrity of the skin at or near stimulation locations (where electrodes are placed) * Treatment for a communicable skin disorder currently or over the past 12 months * Have any irremovable piercings, MRI-contraindicated implantations or metallic based-tattoos * Pregnant or breastfeeding