Date of Degree
PhD (Doctor of Philosophy)
Speech and Hearing Science
J. Bruce Tomblin
The overall aim of the current research was to investigate the corticostriatal system in developmental language impairment (DLI) at the behavioral and neuroanatomical levels. Two groups of young adults, one with DLI (N = 25) and the other without (N = 23), participated in the behavioral study. A sample of procedural learning and reinforcement learning (RL) tasks was selected. Each task represents a unique aspect of procedural memory, and learning processes during these tasks have been linked, at least partially, to the functionality of the corticostriatal system. Findings showed that individuals with DLI demonstrated relatively poor performance on different aspects of procedural learning and on RL. Correlation results provide further evidence for a close relationship between individual differences in implicit learning and individual differences in language. These results implicate an abnormal corticostriatal system in DLI. In the structural imaging study, two subgroups of participants from the first study, one with DLI (n = 10) and the other without (n = 10), were matched on age, gender, and handedness. Conventional magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) were used to investigate the subcortical components of the corticostriatal system in individuals with DLI. Results showed pathological enlargement in the bilateral putamen, the right globus pallidus, and the bilateral nucleus accumbens of individuals with DLI. In addition, the DLI group revealed decreased FA in the globus pallidus and in the thalamus, indicating abnormal white matter integrity in the two subcortical regions. These imaging results underpin the behavioral results, showing corticostriatal abnormalities in DLI at both macrostructural and microstructural levels. In addition to subcortical regions, the four cerebral lobes were also included for an exploratory analysis. Findings showed that individuals with DLI had global diffusion abnormalities in cerebral white matters in the absence of volumetric alterations, and these abnormalities were closely associated with impaired language performance. The results support a role of white matter integrity in language function. In conclusion, individuals with DLI have an abnormal corticostriatal system, which may lead to compromise of a wide variety of cognitive learning, including procedural learning, RL, and certain aspects of language learning.
corticostriatal system, Developmental language impairment, procedural learning, reinforcement learning
xiii, 171 pages
Includes bibliographical references (pages 146-171).
Copyright 2012 Joanna Chen Lee