Aim 1: To determine whether tDCS over the left perisylvian language areas paired with naming treatment will improve oral and written naming outcomes in two variants of PPA (nfvPPA and lvPPA).
The investigators will use a double-blind, sham-controlled, within-subject, cross-over design. Participants will receive Naming and Spelling (NASP) treatment + tDCS condition or NASP treatment + sham condition, in Period 1 or 2, randomized for the Period 1 stimulation condition. Each treatment period will last 3 weeks, with 5 language therapy sessions/week, for 15 sessions in total, and a 3-month (stimulation-free) wash-out time between the two periods of stimulation to evaluate clinically meaningful effects.
Language therapy (NASP treatment) will be delivered by a speech-language pathologist or a trained research associate. The participant will be shown a picture on the screen, asked to orally name it, and subsequently write the name. If the participant cannot, the participant will be asked to provide 3 semantic attributes to reinforce semantic representations, as in Semantic Feature Analysis treatment (Boyle, 2010). If the word still cannot be named or written, the clinician will provide the correct name and spelling and the participant will be asked to repeat or copy it 3 times, in a spell-study-spell procedure (Rapp \& Glucroft, 2009). There will be two word-sets: trained (targeted during therapy) and untrained (not targeted during therapy), both individually tailored to the participant based on severity of spelling deficit. Treatment stimuli will consist of 10-30 words depending on individual severity. General procedures and the outcome measure (letter accuracy) will be maintained across all participants. Consistent with the investigators previous work, the NASP treatment will be conducted in English, which, for most participants, will be the participant's first language.
To deliver tDCS, the investigators will use the Soterix 1x1 platform. The anode will be placed over the left frontal lobe, centered on F7 in the 10-20 electrode placement system (Homan, 1988), and cathode will be placed over the right cheek. Non-metallic, conductive rubber electrodes (5 cm x 5 cm), fitted with saline-soaked sponges to limit skin-electrode reactions will be used so the full left inferior frontal gyrus (IFG) will be covered. Current will be delivered with an intensity of 2 mA (estimated current density 0.08 milliamps (mA)/cm2) for a total of 20 minutes each tDCS session. Delivery of tDCS will be simultaneous with the start of language therapy, which will continue for an additional 25 minutes beyond the cessation of tDCS in each session. In contrast to actual tDCS, sham stimulation involves the delivery of 30 seconds of current ramping up to 2 mA and back down to 0 mA simultaneous with the start of language therapy.
Behavioral/language assessments will involve: oral and written naming, spelling, connected speech/discourse, sentence comprehension and production, verbal fluency, short-term/working memory tasks, etc. Other global cognitive assessments will be conducted, as well as quality of life assessments. Bilingual assessments will be conducted for those who bilingual or multilingual.
Aim 2: To identify clinical, neural, cognitive, biological, and demographic predictors of tDCS vs sham effects on primary outcomes.
Imaging will be performed at before Period 1, before Period 2 and 3-months post Period 2 for a total of 3 scans per participant. Scans will be done on a 3T Philips system and will consist of magnetization prepared rapid gradient echoresting state (MPRAGE), resting state functional MRI (rsfMRI), and diffusion tensor imaging (DTI). Each scanning session will last approximately 1 hour.
Saliva samples will be collected for exploratory analysis and DNA will be extracted using standard methodology. Genotyping will be carried out by the Johns Hopkins DNA Diagnostic Laboratory using standard methods.