Treatment of Memory Retrieval Impairments in MS With HDtDCS to the LIFG in a Placebo Controlled Trial

Inclusion Criteria: * Participants must be between the ages of 18 and 64; * Participants must have a diagnosis of relapsing-remitting multiple sclerosis (RRMS). A physician's note verifying RRMS will be required if they are a patient outside the UT Southwestern network; * Participants must have a validated memory deficit: Validation will be done via neuropsychological testing at the initial/baseline visit using the Semantic Object Retrieval Test (SORT), COWAT (letter and category fluency), Boston Naming Test (BNT), and Auditory Verbal Learning Test (AVLT); neuropsychological test score on at least one verbal retrieval assessment (COWAT, BNT, AVLT) of a T-score less than 40 or a verbal retrieval test that was greater than 1.0 SD below the average T-score on SORT; * Participants must be fluent in speaking and reading English because testing materials are not available in other languages. Exclusion Criteria: * Relapse or acute MS exacerbation during the two months (60 days) preceding the baseline testing, with re-evaluation for inclusion possible after the 60 days of stability; * Less than 3 months (90 days) on a stable dose of benzodiazepines or modaphinil/armodafinil; * A history of a neurological disorder, other than RRMS, including dementia of any type, epilepsy or other seizure disorders, brain tumor, present drug abuse, stroke, blood vessel abnormalities in the brain, Parkinson's disease, or - - Huntington's disease; * Epilepsy or other seizure disorder; * Severe traumatic brain injury; * Unexplained episodes of loss of consciousness; * Suffering frequent headaches; * Unstable or uncontrolled psychiatric illness; * Brain tumor; * Serious or life-threatening diseases, including congestive heart failure, chronic obstructive pulmonary disease, or active malignancy; * Stroke; * Head implant or skull defects/damage that would affect HDtDCS administration or EEG recording; * Use of brain medical device; * Cardiac, neural, or medication implants that would affect HDtDCS administration or EEG recording; * Vascular clip; * Scalp skin condition like dermatitis, psoriasis, or eczema; * Current substance abuse, less than 1 year of discontinuation; Pregnancy; * Cognitive impairment due to an issue other than RRMS; * Telephone-administered Montreal Cognitive Assessment (TMoCA) Score \<19, unless accompanied by a legally authorized representative (LAR) to the consenting session; * Montreal Cognitive Assessment (MoCA) Score \<23, unless accompanied by an LAR to all sessions and both the participant and LAR provide consent; Not being able to give informed consent, unless accompanied by an LAR to all sessions and both the participant and LAR provide consent, and with consent ability assessed with a set of comprehension questions regarding the study and consenting to participate and with MoCA criteria above; * Medication Restrictions: Certain medications can temporarily change how your brain responds to electrical stimulation or affect EEG signals, and therefore are exclusionary: 1) Known medications that interact with tDCS efficacy: anti-convulsants, L-dopa, carbamazepine, sulpiride, pergolide, lorazepam, rivastigmine, dextromethorphan, D-cycloserine, flunarizine, ropinirole; 2) Medications that lower the seizure threshold; 3) Stimulant Medications (e.g., Adderall, Ritalin, often used for MS-related fatigue) cannot be taken during the course of the study; enrollment can be considered if the participant is willing to suspend use over the course of the study and suspension is coordinated with the prescribing physician); suspension must occur at least 3 days before any assessment session and must be maintained over the HDtDCS treatment phases of the study; * Steroid Medications (e.g., Prednisone, Decadron, IV Solu-Medrol, often used for MS relapses or inflammation treatment); If a participant has taken prescription steroid pills or received a steroid IV, they must wait at least 2 months (60 days) after your last dose before you can start tDCS treatments, although baseline testing will permissible within this 2-month waiting period.