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The Neurochemistry of Speech Motor Control in Developmental Stuttering
Poster Session F, Friday, October 2, 2:45 - 4:45 pm, Wangari Maathai
This poster is part of the Sandbox Series.
Nia-Wyn Williams1, Paul Mullins1, Abigail Grant1, Charlie E. E. Wiltshire1; 1Bangor University, Wales
Persistent developmental stuttering (PDS) is characterised by difficulties initiating speech and frequent interruptions to the flow of speech. The imaging literature has reported both functional and structural differences in a network of speech-motor related regions, inspiring the cortico-basal ganglia-thalamocortical motor loop model of PDS (Chang & Guenther, 2020). This loop works to coordinate the initiation and termination of speech motor programmes. Theoretically, impairment in this neural loop could disrupt accurate motor programme execution or selection, resulting in the speech “blocks”, prolongations, and repetitions characteristic of PDS. The execution of the appropriate motor programs is actively managed by a series of inhibitory and excitatory projections through the four components of the cortico-basal ganglia-thalamocortical motor loop: the inferior frontal gyrus, basal ganglia, motor cortex, and the thalamus. Signalling through these projections is managed through the concentrations of the neurotransmitters GABA, and glutamate, which are mediated by dopaminergic projections to the basal ganglia via GABAergic neurons. Dopamine levels within the cortico-basal ganglia-thalamocortical motor loop have shown to be altered in PDS (Clear et al., 2021; Civier et al, 2013; Wu et al., 1995). It is therefore possible that inhibitory and excitatory signally is altered in PDS, resulting in inefficient or disrupted motor programme selection and suppression. Importantly, differences in GABA and glutamate concentrations and their relationship with dopamine has yet to be directly investigated in PDS. We used magnetic resonance spectroscopy (MRS) to measure concentrations of GABA and glutamate in the basal ganglia, inferior frontal gyrus, and supplementary motor area of 30 people who stutter and 30 fluent speaking controls (30x25x20mm voxels; MEGA-PRESS). We also employed multi-parameter mapping for the quantification of iron deposition (as a proximal measure of dopamine) in homogeneous ROIs and whole-brain analyses. MEGA-PRESS data were referenced to water and analysed using SPANT. The SPM hMRI toolbox was used for the quantification of R2* for the MPM data. We hypothesise that concentrations of GABA, glutamate, and iron will be altered in people who stutter. We also hypothesise that these measures will be correlated with each other as well as with stuttering severity. To date, preliminary analysis has been completed for half of the sample. We will use Bayesian hierarchal mixed modelling on the full sample to estimate the effect of group differences on GABA, glutamate, and dopamine concentrations, as well as their relationship to each other. These findings are expected to significantly advance our understanding of the neurochemical and microstructural basis of both fluent speech and PDS, providing much needed evidence for recent theories underpinning PDS.
Topic Areas: Speech Motor Control, Disorders: Developmental