Presentation

Sara Pillay¹, Xin Ran Li¹, Priyanka Shah-Basak¹, Joe Heffernan¹, Lisa Conant¹, Anna Frieberg¹, Shelley Laitinen¹, Samantha Hudson¹, Jed Mathis¹, Sabine Heuer², Roy Hamilton³, Jeffery Binder¹; ¹Medical College of Wisconsin, ²University of Wisconsin-Milwaukee, ³University of Pennsylvania

Difficulty retrieving the correct phonological information for speech production is a common deficit after left hemisphere stroke causing damage to posterior perisylvian cortical regions. In a recent fMRI study of people with aphasia (PWA) with primarily phonological system damage and preserved semantic function, the left angular gyrus (AG) was activated more when participants correctly read words aloud than when they made errors (Pillay, et al., Journal of Cognitive Neuroscience, 2018). This suggests that activation within the perilesional semantic system promotes or ‘boosts’ phonological retrieval when the phonological retrieval system is damaged. We hypothesized that applying high-definition transcranial direct current stimulation (HD-tDCS) to the AG while patients received semantic-focused speech therapy (Semantic Feature Analysis, SFA) would promote reorganization of semantic networks and increase connectivity between semantic and phonological networks. We used resting-state fMRI (rs-fMRI) and detailed language assessment to examine the persistent changes of this intervention. Four PWA with phonological impairment from chronic left middle cerebral artery stroke received two 10-day cycles of SFA therapy during anodal HD-tDCS (4x1 montage, 2mA, 20 min) to the left AG or sham/control HD-tDCS in a cross-over design. All participants were left-hemisphere dominant for language pre-therapy based on a well-validated fMRI language task protocol. Functional connectivity fMRI and language assessments were completed at 3 times (pre-therapy, 10 weeks after cycle 1, 10 weeks after cycle 2). Participants were trained on words and pictures that were baseline-tested twice using an adaptive procedure to identify items they reliably could not name, and to ensure that the items chosen represented an optimal level of difficulty. Matched untrained lists were created to assess generalization. Twenty minutes of rs-FMRI data from each session were denoised using ICA-AROMA. Pairwise connectivity was computed between Brainnetome atlas parcels comprising the left semantic (Lsem) and phonological (Lphon) networks and their right hemisphere homologs (Rsem and Rphon). After AG-tDCS, significant connectivity increases were observed within Lsem and between left and right Sem networks. Connections between Lsem and Rphon and between Rsem and Rphon became more negative (inhibitory). After sham/control-tDCS, connections increased within Rsem networks and became less inhibitory between Rsem and Rphon networks. Other network changes after either AG or control-tDCS were variable across participants. Mild to moderate gains on untrained items were observed across all participants, with slightly better performance after AG-tDCS (Mean change, words: 38%, pictures: 26%) compared to control/sham cycles (Mean change, words: 27%, pictures: 5%). The study is ongoing, and some procedures are incomplete for two of the participants at the time of submission. These preliminary results suggest that stimulation of a left-hemisphere semantic region during SFA therapy increases intra-hemispheric and inter-hemispheric semantic connections, while inhibiting connections with the right phonological system. These changes were associated with improved performance on untrained reading and picture naming items. Additional data are needed to identify significant correlations between behavioral and functional connectivity changes.

Topic Areas: Language Therapy, Meaning: Lexical Semantics