TABLE 1.

Past tDCS studies with primary progressive aphasia (PPA) participants.

Study	Participants	Training	Anode	Cathode	Intensity	Duration	Sessions	Outcome
Wang et al. (2013)	One non-fluent PPA	Refused training	Morning: Left posterior perisylvian region Afternoon: Left broca’s area	Extracephalic: Right shoulder	1.2 mA	20 min	5 sham 5 tDCS	Auditory word-picture identification, picture naming, oral word reading, and word repetition all improved after administering tDCS; decline 2 months post-stimulation
Cotelli et al. (2014)	16 Agrammatic PPA	Speech therapy: repetition of target word, articulatory suppression, picture naming, reading words	Left dorsolateral prefrontal cortex	Extracephalic: Right arm	2 mA	25 min	10 sessions of either sham or tDCS	Improvement for treated items was greater for anodal tDCS than sham tDCS, for untreated items, both montages had similar levels of improvement
Tsapkini et al. (2014)	Two non-fluent PPA, four logopenic PPA	Participants wrote a letter or letter combination corresponding to a given phoneme	Left inferior frontal gyrus	Extracephalic: Right cheek	2 mA	20 min	15 sessions each condition (tDCS and sham)	Improved Spelling; improvements greater and lasted longer (2 months) in real condition, untrained items improved in real condition only
Gervits et al. (2016)	Two non-fluent PPA, four logopenic PPA	Narrating wordless children’s picture books	Left frontotemporal region	Left occipitoparietal region	1.5 mA	20 min	10 sessions of tDCS	Improvements in speech production and grammatical correctness lasting 3 months; no sham condition
Teichmann et al. (2016)	12 semantic PPA	Simple visuomotor task: Press a button when a particular object reaches the edge of the screen. Done to maintain vigilance.	Session 1: Left temporal (FT7 to FT9) Session 2: Left fronto-orbital	Session 1: Right frontoorbital Session 2: Right temporal (FT8 to FT10)	1.59 mA	20 min	3 sessions (one session per condition)	Compared to sham, tDCS sessions improved responses to questions written in a verbal format on a semantic matching task, reaction times to questions regarding living items were faster after anode fronto-orbital and cathode right temporal stimulation.
Roncero et al. (2017)	Six non-fluent PPA, two logopenic PPA, two semantic PPA	Repeated naming of items incorrectly named at that day’s session	Left inferior parietotemporal region	Right frontoorbital region	2 mA	30 min	10 sessions each Condition (tDCS and sham)	Picture naming scores for trained and untrained items improved more in the real condition; lasting at least 2 weeks
Hung et al. (2017)	One logopenic PPA, three semantic PPA, one early onset AD	Repeated spontaneous naming, sentence production, and semantic feature generation	Left temporoparietal region	Centered over the forehead	1.5 mA	20 min	10 sessions of tDCS	Improved naming for trained items lasting 6 months; there was no sham condition. Zero improvement for untrained items. No change observed for early onset AD participant.
McConathey et al. (2017)	Six non-fluent PPA, one logopenic PPA	Narrating wordless children’s picture books	Left frontotemporal region	Left occipitoparietal region	1.5 mA	20 min	10 sessions of either sham or tDCS	Individuals who scored low at baseline had greater propensity to improve when given real tDCS relative to sham tDCS
Tsapkini et al. (2018)	14 non-fluent PPA, 12 logopenic PPA, 10 semantic PPA	Confrontation verbal and written naming; errors corrected and repeated	Left inferior frontal gyrus	Extracephalic: Right cheek	2 mA	20 min	15 sessions each condition (tDCS and sham)	Written naming letter accuracy for trained and untrained items improved for logopenic and non-fluent PPA, no change found for semantic PPA