Effect of Transcranial Direct Current Stimulation on Motor Speech in Nonfluent Primary Progressive Aphasia: A Case...

Primary progressive aphasia (PPA) is a neurodegenerative disorder that causes a gradual decline in language function. While combining transcranial direct current stimulation (tDCS) with rehabilitation of speech and language disorders (SLD rehab) has shown promise, its effect on motor speech disorders such as dysarthria and apraxia of speech (AOS), common in nonfluent variant PPA (nfvPPA), has been unclear.

This study used an N-of-1 crossover design to investigate the effects of SLD rehab-tDCS on articulation and vocalization in a 77-year-old male patient with nfvPPA, dysarthria, and AOS. In the intervention phase, intervention A (anodal tDCS over the left inferior frontal gyrus from the precentral regions, combined with SLD rehab) was compared with intervention B (sham stimulation with SLD rehab) across both short-term (single session) and long-term (12 sessions over 6 weeks) phases, with intervention A preceding B. In both the short- and long-term phases, the assessments of articulation and vocalization showed greater improvement following intervention A. The long-term intervention also led to improvements in general aphasia severity. Furthermore, brain perfusion SPECT imaging revealed increased blood flow in the left fronto-subcortical network.

These preliminary findings from a single case suggest that SLD rehab-tDCS may have the potential to improve not only language but also speech motor functions in nfvPPA.