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Delta HD-tACS modulates auditory-motor integration in adults who stutter
Poster Session B, Wednesday, September 30, 4:30 - 6:30 pm, Wangari Maathai
Emily Garnett1, Yanni Liu1, Hasini Weerathunge1, Yuan Tan1, Soo-Eun Chang1; 1University of Michigan
Effective treatment options remain limited for stuttering, a neurodevelopmental disorder that can result in substantial psychosocial and occupational consequences across the lifespan. Previous studies have pointed to disrupted auditory-motor integration in stuttering, where reduced structural and functional connectivity between auditory-motor areas were reported with neuroimaging, while behavioral studies have shown evidence of reduced auditory-motor/sensorimotor adaptation in response to altered auditory feedback, as well as fluency improvements during rhythmic cueing (e.g., choral speech). Speech production depends on coordinated neural oscillations across distributed cortical regions. Delta rhythms (1-4 Hz) are thought to support temporal prediction and auditory-motor integration during speech. Because speech relies on predictive auditory-motor coordination, effective communication between auditory and speech-motor regions likely depends not only on synchronization, but also on precise temporal relationships between regions. The present study tested whether modulating oscillatory coordination between auditory and premotor cortices using dual-site high-definition transcranial alternating current stimulation (HD-tACS) could improve speech fluency and auditory-motor function in adults who stutter. During stimulation, participants completed choral reading, a fluency-enhancing task known to engage auditory-motor speech networks. Stimulation was delivered at delta frequency under three conditions: in-phase stimulation, in which oscillatory activity across premotor and auditory regions was synchronized; anti-phase stimulation, in which the regions were driven 180 degrees out of phase; and sham stimulation, consisting of 30-second ramp-up/down stimulation periods at the beginning and end of the session only. To probe auditory-motor integration and temporal processing, participants also completed a speech (first formant frequency) perturbation task, which indexes adaptive responses to altered auditory feedback, and a rhythm discrimination task, which assesses perceptual timing abilities linked to beat-based processing and delta-timescale temporal prediction. We tested whether active delta-frequency HD-tACS over auditory and premotor cortices modulated behavioral indices of auditory-motor integration relative to sham, with stimulation phase relationship examined as an exploratory factor. Fifteen adults who stutter have completed the full study, and data collection is ongoing. Preliminary analyses indicate that anti-phase HD-tACS (vs. sham) improves rhythm discrimination (increased d’) and enhances compensatory responses during the perturbation task. EEG and speech fluency (e.g., SSI-4 scores, percent stuttered syllables, naturalness, self-rated severity) analyses are ongoing. These preliminary findings suggest that effective auditory-motor communication for speech may depend on the temporal dynamics between auditory and speech-motor regions rather than simply increasing synchrony between them. Because speech production relies on predictive coordination between motor commands and incoming auditory feedback, anti-phase stimulation may better support the natural timing dynamics required for efficient auditory-motor integration, whereas in-phase stimulation may impose a less effective coordination pattern. More broadly, the results support the possibility that targeted modulation of oscillatory coordination within auditory-motor networks may represent a promising mechanistic intervention approach for stuttering.
Topic Areas: Speech Motor Control, Disorders: Developmental