HD-tDCS Word Retrieval Outcomes in PPA

Christine Sofka Dugas^1*Hsueh-Sheng Chiang²Paulina Devora³Katelyn Lucas-Mendoza¹Christine Abasi¹Ashna Adhikari³Trung Nguyen²Alexander Frolov²Brendan J Kelley²Christian LoBue²Raksha Anand Mudar⁴John Hart^1,2

• ¹Department of Speech, Language, and Hearing, School of Behavioral and Brain Sciences, The University of Texas at Dallas, Richardson, United States
• ²The University of Texas Southwest Medical Center, Dallas, Texas, United States
• ³The University of Texas at Dallas, Richardson, Texas, United States
• ⁴University of Illinois Urbana-Campaign, Campaign, Illinois, United States

Background: Word retrieval deficits are the most prominent symptoms reported in primary progressive aphasia (PPA) and related syndromes. Current treatments, such as speech and language therapy, have shown limited success, highlighting the need for alternative non-pharmacological interventions with high-definition transcranial direct current stimulation (HD-tDCS) emerging as a promising tool.Objective: This study aimed to evaluate the effects of HD-tDCS on word retrieval function in individuals with PPA by comparing two stimulation sites: the presupplementary motor area (pre-SMA) and the left inferior frontal gyrus (LIFG), and to assess the relative benefits of each site.: Eight individuals with PPA underwent 10 sessions of open-label HD-tDCS targeting either the LIFG (n = 4) or pre-SMA (n = 4). Word retrieval was assessed at baseline, immediately post-stimulation, and at 8-week follow-up. Electrophysiological measures, including event-related potentials during a non-verbal Go-NoGo task, were also collected to explore neural mechanisms. Results: LIFG stimulation yielded statistically significant improvements in phonemic fluency at immediate post testing compared to baseline, with 25-50% showing clinically meaningful improvement. Clinically meaningful improvement was observed in category fluency in 25-50% of the patients receiving stimulation at either site. Lastly, electrophysiological measures indicated HD-tDCS targeting LIFG differentially modulated event-related potential effects during non-verbal Go-NoGo tasks.This research provides preliminary evidence supporting the use of both traditional (LIFG) and alternative (pre-SMA) stimulation sites for treating word retrieval deficits in individuals with PPA. The findings also suggest potential neural mechanisms of HD-tDCS intervention, which can inform future designs of non-invasive brain stimulation for cognitive symptoms in PPA.