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Cerebellar involvement in speech production
Poster Session A, Friday, September 12, 11:00 am - 12:30 pm, Field House
Sivan Jossinger1, Jorn Diedrichsen1; 1Western University
Producing speech is a multifaceted process that involves lexical selection, phonological planning, and articulatory execution. This ability depends on both language proficiency and complex motor functioning, utilizing a large network of brain regions. Clinical evidence indicates that both the cerebellum and the neocortex are critical nodes in this network. Ataxic dysarthria, a speech disorder primarily characterized by slowed and distorted articulation, is the hallmark of cerebellar damage. However, similar articulatory distortions have also been observed in patients with neocortical lesions. Likewise, while impaired verbal fluency (i.e., the ability to generate words under specific task demands) is typically associated with frontal lobe dysfunction, it has also been documented in cerebellar patients, even when controlling for their dysarthria severity. Therefore, the question of the distinct contribution of the cerebellum and neocortex to speech production remains unknown. To address this question, we use functional magnetic resonance imaging (fMRI) to measure the whole brain response during overt production of nine-syllable utterances. We vary multiple factors of these syllable strings that may characterize cerebellar contribution. First, we test three speeds of production to test the idea that the cerebellum especially contributes to fast speech production. Secondly, we vary the complexity of the syllabic sequence, using either the same syllable three times (simple sequence; e.g. ‘ta-ta-ta’) or a string of three unique syllables (complex sequence; e.g. ‘ta-bo-go’). Third, we will examine lexical familiarity, utterances will either form trained real words (e.g., "bo-go-ta"), or novel, untrained pseudowords (e.g., "ta-bo-go"). Finally, to disentangle lexical effects from motor training, participants will be extensively trained on the overt production of certain pseudowords. We will use the selective recruitment analysis approach to evaluate the unique contribution of the cerebellum to speech articulation. This method uses the prediction from a task-invariant cortical-cerebellar connectivity model as baseline. If the cerebellum is specialized for a specific aspect of speech production, distinct from the neocortex, it should show higher-than-expected activity in a designated task compared to the baseline connectivity. We hypothesize that the cerebellum will be selectively recruited at production rates higher than 3Hz, as cerebellar patients show a reduced articulation rate that reaches a plateau at ~2.5-3 Hz. Furthermore, given the cerebellum’s role in sequence learning, we expect enhanced cerebellar activity during the production of novel, complex pseudoword sequences. In contrast, we do not anticipate cerebellar selectivity during the production of real words, regardless of their complexity. Similarly, we predict equivalent cerebellar activation for trained syllabic sequences, whether they constitute real words or pseudowords. The results of this investigation will provide novel insights into the cerebellum’s role in speech production. Pinpointing the specific aspects of speech production governed by the cerebellum paves the way for developing rehabilitation programs for patients with ataxic dysarthria.
Topic Areas: Speech Motor Control, Language Production