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Divergent oscillatory dynamics reveal a complexity-dependent practice effect during speech motor planning
Poster Session F, Friday, October 2, 2:45 - 4:45 pm, Wangari Maathai
This poster is part of the Sandbox Series.
Rahulkrishna G. Thimmugari1, Peter E. Turkeltaub1,2, Andrew T. DeMarco1; 1Center for Brain Plasticity and Recovery, Georgetown University, 2Research Division, MedStar National Rehabilitation Hospital
Speech motor planning (SMP) is an intermediate phase in language production (Van Der Merwe, 2021). The GODIVA model claims that two distinct SMP process types, segmental and suprasegmental, occur in limited capacity buffers (Miller & Guenther, 2021). SMP is well-known to be characterized by a decrease in μ-band (8-30 Hz) oscillatory power (desynchronization). However, neural investigations of SMP are largely limited to behavioral/structural studies, which are unable to assess the GODIVA model’s claims regarding SMP dynamics. In this study, we evaluate μ-band task-related power changes (μPC) in relation to SMP process type and motor plan complexity (hereafter, complexity), using time-frequency analysis on scalp EEG in neurotypical individuals. Below, we present pilot data (n=1) evaluating the hypothesis that higher complexity items will induce greater desynchronization. Our ultimate goal is to characterize SMP dynamics in neurotypical individuals to complement parallel work understanding SMP deficits in post-stroke Apraxia of Speech (AOS). A delayed-naming task is completed in which target real words are presented and read aloud following a delayed cue. Fifteen real word stimuli are presented with 16 repetitions each and are manipulated by complexity (low/medium/high). EEG is acquired through a 64-channel BrainVision ActiCHamp system, preprocessed using a custom pipeline in EEGLAB, and epoched relative to response-locked speech onset. Activity in left and right sensorimotor electrodes is averaged to form two clusters, on which time-frequency decomposition is performed. Power is averaged across the μ-band and z-scored relative to baseline average. Linear mixed-effects modeling is conducted to ascertain statistical significance: μPC~complexity*number of repetitions+(1|stimulus). μPC is defined as the trial-level instantaneous power at cue presentation minus target presentation. A negative μPC indicates desynchronization while a positive μPC indicates μ-band power increase (synchronization). Results show a trending main effect of complexity (p=0.059, estimate=-0.287) and no main effect of repetition number (p=0.199, estimate=0.042). However, the model shows a significant complexity x repetition interaction effect (p=0.014, estimate=-0.097), indicating that complexity predicts desynchronization but only at later repetitions. Specifically, while we saw desynchronization for high complexity items, the interaction effect was primarily driven by synchronization for low complexity items. The direction of the interaction effect is consistent with the classic desynchronization findings in motor control (Pfurtscheller & Lopes Da Silva, 1999), with our model finding a trending effect of overall μPC (p=0.080, estimate=0.369). Synchronization for low complexity items after repeated practice may reflect the retrieval of a well-learned motor memory as opposed to constructing a motor plan online, while desynchronization for high complexity items even after repeated practice suggests that complex motor plans continue to require active motor planning. This interpretation suggests that simple real word motor plans are easily consolidated into stable, stored motor programs, which interferes with our goal of studying SMP dynamics. Therefore, we plan to alter stimulus design such that pseudowords are presented with no repetitions and SMP process type (segmental/suprasegmental) is crossed with complexity (low/medium/high). Data from 10 participants using this design will be presented on the poster. Next steps include utilizing this design to understand how SMP dynamics are altered in AOS.
Topic Areas: Speech Motor Control, Disorders: Acquired