Selective Functional Network Changes Following tDCS-Augmented Language Treatment in Primary Progressive Aphasia

Area of Science:

• Neuroscience
• Neurology
• Cognitive Science

Background:

• Primary progressive aphasia (PPA) is a neurodegenerative syndrome primarily affecting language.
• Transcranial direct current stimulation (tDCS) shows promise as an adjunct to behavioral therapy for neurodegenerative diseases.
• Neural mechanisms and neuroimaging evidence for tDCS in PPA remain sparsely understood.

Purpose of the Study:

• To investigate tDCS-induced neural changes in PPA during language intervention.
• To test the hypothesis that tDCS promotes system segregation in the language network.
• To examine tDCS effects on functional network connectivity of the left inferior frontal gyrus (LIFG).

Main Methods:

• Resting-state fMRI data collected from 32 PPA participants before and after therapy with tDCS or sham stimulation.
• Analysis focused on the global connectivity (participation coefficient) of the left LIFG-triangularis (LIFG-tri) region.
• Compared pre/post treatment connectivity within groups and with 19 healthy controls.

Main Results:

• Higher baseline LIFG-tri connectivity correlated with greater dementia severity.
• The tDCS group exhibited a significant decrease in LIFG-tri global connectivity post-treatment; the sham group did not.
• This decrease reflected reduced connectivity with extra-perisylvian regions, supporting enhanced language system segregation.

Conclusions:

• tDCS-augmented language therapy promotes functional segregation of the language system in PPA.
• This normalization of pre-treatment hyper-connectivity suggests improved processing efficiency.
• Findings support tDCS efficacy and inform future non-invasive brain stimulation (NIBS) treatment designs.