Search Abstracts | Symposia | Slide Sessions | Poster Sessions
Synchronizing language networks: Alpha tACS reduces semantic competition during word retrieval
Poster Session C, Thursday, October 1, 10:45 am - 12:45 pm, Wangari Maathai
Denise Y. Harvey1, Rosie Lynch1, Mihir Mishra1, Mehtaab Rakkar1, Roy Hamilton1; 1University of Pennsylvania
Word retrieval requires selecting a target word from amongst simultaneously activated semantic competitors. This competition is reflected behaviorally as semantic interference, whereby naming in semantically related vs. unrelated contexts is slower and more error prone. In aphasia, exaggerated semantic interference has been proposed to reflect impaired selection among competing lexical representations and has been linked with damage within frontotemporal language regions—notably the left inferior frontal gyrus (LIFG)—involved in lexical selection. Consequently, semantic competition has emerged as a potentially important mechanistic target for aphasia interventions. Separately, there is growing interest in utilizing noninvasive brain stimulation, including transcranial direct current stimulation, to facilitate aphasia recovery. However, therapeutic effects remain variable, partly due to limited understanding of how stimulation influences language processing. Transcranial alternating current stimulation (tACS)—a more recent form of neuromodulation—delivers a weak sinusoidal waveform designed to interact with endogenous neural oscillations and may better modulate language-network dynamics. Converging evidence suggests that alpha-band oscillations (8–13 Hz) support long-range cortico-cortical communication critical for coordinating large-scale cognitive processes, including language production. However, whether alpha-band oscillations play a mechanistic role in resolving semantic competition remains unknown. We tested whether alpha-tACS alters semantic competition during word retrieval and whether behavioral effects relate to stimulation-induced changes in alpha-band activity and functional connectivity. Twenty healthy older adults (10 female; mean age = 59.2 years) completed a double-blind, sham-controlled, within-subject crossover study. Participants received stimulation at their individual alpha frequency (4 mA peak-to-peak) via a 5-electrode montage targeting the left hemisphere language network. Resting-state EEG was recorded pre-, mid-, and post-stimulation. During stimulation, participants completed two language production tasks that engage frontotemporal language networks (Sentence Completion and Verb Generation). Following stimulation, participants completed a Blocked-Cyclic Naming (BCN) task and a non-linguistic control task. Response times were analyzed using linear mixed-effects models. Resting-state alpha power and alpha-band weighted phase lag index (wPLI) connectivity were additionally examined using F7-seeded—approximating the LIFG—connectivity analyses. Active tACS reduced semantic competition during the BCN task relative to sham stimulation (p = .031). TACS had no effect on online language measures (p’s > .18) or the offline control task (p > .94). Active stimulation additionally produced a significant immediate post-stimulation increase in alpha power at F7 (p < .01). Behavioral and neurophysiological effects exhibited substantial interindividual variability. Resting-state connectivity analyses further suggested that participants exhibiting larger active-stimulation increases in F7-seeded alpha-band connectivity across left hemisphere language-network regions also demonstrated marginally larger reductions in semantic interference (Spearman’s ρ = .42, p = .066). No comparable relationship was observed during sham stimulation (p > .16). The present findings suggest that alpha-tACS induced transient oscillatory entrainment of the language network accompanied by behavioral aftereffects on semantic competition during language production. Preliminary connectivity findings suggest that alpha-tACS may modulate lexical retrieval partly through changes in frontotemporal alpha-network communication. Together, the findings support semantic competition as a mechanistically relevant neuromodulation target and motivate language-network stimulation protocols for translational aphasia research.
Topic Areas: Language Production, Control, Selection, and Executive Processes