Treating lexical retrieval using letter fluency and tDCS in primary progressive aphasia: a single-case study

Background: In early stages, individuals with primary progressive aphasia (PPA) report language symptoms while scoring within norm in formal language tests. Early intervention is important due to the progressive nature of the disease. Method: We report a single-case study of an individual with logopenic variant PPA (lvPPA). We tested whether letter fluency, used as a therapy task, can improve lexical retrieval when combined with tDCS to either the left inferior-frontal gyrus (IFG) or the left inferior parietal lobe (IPL), administered in two separate therapy phases separated by a wash-out period of 3 months. Outcomes and results: We observed increases in number of words retrieved during a letter fluency task in trained and untrained letters, when letter fluency therapy (LeFT) was administered with anodal tDCS. When LeFT was combined with left IFG stimulation, words produced in a letter fluency task were lower frequency and higher age of acquisition after treatment, compared to before treatment and there was also an increase in accuracy and response times in an untrained picture-naming task. Conclusions: The results indicate that letter fluency therapy combined anodal tDCS is effective in improving lexical retrieval, particularly when left IFG stimulation was used. Effects generalize beyond the trained task, albeit slowing down of responses in picture naming. This task may provide a useful clinical intervention strategy for patients with mild anomia, who are not challenged enough by traditional naming therapies.