Remotely-supervised Neuromodulation in PPA

The goal of this clinical trial is to learn whether home-based brain stimulation combined with virtual speech-language therapy can improve communication abilities in adults with logopenic variant primary progressive aphasia (lvPPA), a language disorder most often caused by Alzheimer's disease. The main questions the study aims to answer are: * Is combining remotely supervised transcranial direct current stimulation (tDCS) with virtual speech-language therapy feasible and acceptable for people with lvPPA? * Does this combined treatment lead to improvements in communication compared to speech-language therapy with sham (placebo) stimulation? * Do individual brain characteristics help predict who benefits most from this treatment? Researchers will compare participants who receive active tDCS plus virtual speech-language therapy to participants who receive sham (placebo) tDCS plus virtual speech-language therapy to see if active brain stimulation enhances communication outcomes. Participants will: * Complete speech-language therapy sessions delivered by video visit. * Receive either active or sham tDCS that is remotely supervised and completed at home. * Complete language and cognitive testing before and after treatment. * Undergo brain imaging and other assessments to help understand treatment response.