Predictors of Speech Motor Sequence Learning in Neurological Disorders

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Project Summary For the many Americans living with neurogenic speech disorders, the simple task of talking—producing a sequence of speech sounds—presents significant barriers in daily life. Therefore, learning to produce new sound sequences (such as those in a difficult word) is a central component of speech rehabilitation. However, the mechanisms underlying speech motor sequence learning are poorly understood despite the critical importance of this process to speech therapy. Accurate speech production involves both a phonological encoding stage to plan and sequence upcoming sound units (i.e., phonemes) and a motor programming stage to transform the planned phonemes into precise motor movements. It remains unclear how these two stages interact to support the learning of new speech sequences. The primary objective of this proposal is to differentiate the roles of phonological planning and speech motor programming processes during speech motor sequence learning in patients with primary progressive aphasia (PPA). PPA is a category of neurodegenerative disease in which the location and degree of brain atrophy is closely tied to specific speech-language impairments in each individual, and thus allows for relatively precise localization of speech-language function. Patients with PPA may have isolated phonological impairment (e.g., logopenic-variant PPA) or motor programming impairment (e.g., progressive apraxia of speech), or may have relatively intact speech. In this project, participants will complete a two-day learning paradigm where they will practice novel syllables containing non-native consonant clusters that do not occur in English. Improvements in the accuracy and speed of practiced consonant clusters will be compared to their performance on syllables containing untrained non-native consonant clusters. The central hypothesis, based on the GODIVA model of speech sequencing, is that phonological learning should result in reduced utterance duration while motor program learning should result in improved accuracy. This project will test this hypothesis through two specific aims: 1) determine the behavioral predictors of speech motor sequence learning abilities, and 2) establish the neural correlates of these abilities. Aim 1 will test the relationship between learning measures and common clinical measures of phonological and motor programming ability. Aim 2 will analyze the relationship between learning measures and the degree of cortical thinning in phonological and motor programming brain regions. This study will further our knowledge of the mechanisms involved in speech motor sequence learning, in line with the NIDCD mission to advance our understanding of normal and disordered speech and improve the lives of individuals with communication disorders. This proposal will also provide crucial training in areas including structural neuroimaging methods and neurodegenerative speech disorder research that are essential for the trainee’s successful transition to an independent research career.