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Exploring the Effects of Anodal tDCS on Left Temporoparietal Cortex Function in Logopenic Variant Primary Progressive Aphasia (LvPPA): A Magnetoencephalography (MEG) Study
Poster B81 in Poster Session B, Tuesday, October 24, 3:30 - 5:15 pm CEST, Espace Vieux-Port
Vahab YoussofZadeh1, Priyanka P. Shah-Basak1, Sara B. Pillay1, Joseph Heffernan1, Candida Ustine1, Peter Kraegel1, Shelby Schold1, Samantha Hudson1, Kimberly D. Mueller2,3, Chrysanthy Ikonomidou4, Mason Fellmeth1, Jeffrey R. Binder1, Manoj Raghavan1, Elias D. Granadillo1,5; 1Neurology, Medical College of Wisconsin, Milwaukee, WI, USA, 2Wisconsin Alzheimer's Institute, School of Medicine and Public Health, University of Wisconsin-Madison Madison, Wisconsin, USA, 3Department of Communication Sciences and Disorders, University of Wisconsin-Madison Madison, Wisconsin, USA, 4Neurology, University of Wisconsin-Madison, Madison, WI, USA, 5Institute for Clinical and Translational Research, University of Wisconsin-Madison, Madison, WI, USA
Logopenic variant primary progressive aphasia (lvPPA) is characterized by difficulties in language production, specifically in the phonological domain. Individuals with lvPPA face challenges in accessing and retrieving words from their mental lexicon, resulting in difficulties with naming, propositional speech, and impaired sentence comprehension due to phonological short-term memory deficits. Previous research has suggested that transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, holds promise for improving language abilities in individuals with aphasia caused by stroke or neurodegenerative conditions. However, the precise neural mechanisms underlying this effect, particularly the impact of tDCS on language processing, remain incompletely understood. This study aimed to investigate the effects of anodal tDCS, which enhances cortical excitability, on the neural correlates of auditory word recognition using magnetoencephalography (MEG) in patients diagnosed with lvPPA. Four individuals with lvPPA underwent MEG scanning while performing an auditory word recognition task. MEG scans were conducted both before and after receiving either anodal or sham high-definition tDCS (HD-tDCS) over the left posterior parietal lobe in daily treatment sessions over two weeks, along with concurrent training on nonword repetition. The MEG task involved listening to 120 words and pressing a button when one of the five target words was recognized. Word presentation occurred in three blocks, each consisting of 40 distractor words and five target words. The distractor words were semantically and phonologically unrelated to the target words. The analysis focused on the event-related fields of the distractor responses. The source magnitudes of the regions adjacent to the stimulation sites in the left parietal lobe, as well as the laterality index (LI) of the temporoparietal network, were compared between the anodal and sham post-stimulation responses. MEG responses to word stimuli revealed consistent engagement of a left temporoparietal network in all patients, both before and after each two-week tDCS cycle. Following anodal stimulation, there was an increase in response magnitudes in the left parietal region compared to the baseline condition, ranging from approximately 20% to 50%. Conversely, only one out of the four participants exhibited increased response magnitudes in the same regions after the sham stimulation. In comparison to sham stimulation, anodal stimulation resulted in response magnitudes that were 10% to 70% higher in all four patients. When examining LI values within the temporoparietal network between the pre- and post-stimulation conditions, three out of four participants demonstrated increased (more left-lateralized) LI after anodal stimulation, while the same percentage exhibited decreased LI after the sham stimulation. Anodal stimulation also led to enhanced left hemispheric dominance, ranging from 9% to 16%, when compared to sham stimulation. These findings suggest that anodal stimulation has the potential to promote brain plasticity, leading to increased functional engagement in targeted regions during task performance. However, further research is needed to validate these findings using a larger sample of individuals with lvPPA. It is also important to determine whether the observed enhancement of cortical engagement in the left temporoparietal network, induced by anodal tDCS, translates into measurable improvements in behavioral performance on language tasks.
Topic Areas: Speech-Language Treatment, Computational Approaches