Targeting Language-specific and Executive-control Networks With Transcranial Direct Current Stimulation in Logopenic Variant PPA

Inclusion Criteria: * Must be between 50-80 years of age. * Must be right-handed. * Must be proficient in English. * Must have a minimum of high-school education. * Must be diagnosed with Primary Progressive Aphasia (PPA) or dementia. * Participants will be diagnosed with PPA or with any of the PPA variants in specialized or early dementias clinics at Johns Hopkins University or other specialized centers in the US based on the current consensus criteria. * Healthy age- and education-matched controls: The investigators will include 30 healthy age- and education-matched controls, usually spouses, to maximize similarity in terms of other demographic or life-style factors that contribute to language and cognitive performance. Exclusion Criteria: * People with previous neurological disease including vascular dementia (e.g., stroke, developmental dyslexia, dysgraphia or attentional deficit). * People with uncorrected hearing loss * People with uncorrected visual acuity loss. * People with advanced dementia or severe language impairments: Mini Mental State -Examination (MMSE)\<18, or Montreal Cognitive Assessment (MOCA)\<15, or language Frontotemporal Dementia specific - Clinical Dementia Rating (FTD-CDR)\<=2. * Left handed individuals. * People with pre-existing psychiatric disorders such as behavioral disturbances, severe depression, or schizophrenia that do not allow these people to comply or follow the study schedule and requirements such as repeated evaluation and therapy. Exclusion Criteria for MRI Participation: * People with severe claustrophobia. * People with cardiac pacemakers or ferromagnetic implants. * Pregnant women.