UC San Diego

Language is a complex process and a unique human ability. However, this intricate process can become impaired, leading to significant challenges in comprehension and expression. This dissertation focuses on the brain basis of language impairments across two distinct populations: adults with post-stroke aphasia and children with Developmental Language Disorder (DLD). These populations are etiologically distinct; adults with aphasia have acquired language impairments in an established language and neural system, while children with DLD have language impairments in a developing language and neural system. The dissertation consists of four studies that investigate the brain functions supporting language, focusing on cerebral blood flow (CBF) in both groups and functional connectivity in children with DLD, to better understand the relationship between these measures and language abilities. Chapter 1 emphasizes the importance of characterizing baseline CBF values in individuals with aphasia. This study demonstrates how regions distal to the site of neural damage exhibit reduced CBF, which contributes to resultant language abilities, highlighting the critical need to properly characterize CBF patterns in clinical populations. In Chapter 2, the focus shifts to children with DLD. The neural underpinnings of DLD are not well understood, thus this chapter synthesizes over 50 years of behavioral and neural research in DLD to identify key brain regions of interest (ROIs) and language deficits that characterize the disorder. Chapter 3 builds on these identified ROIs, exploring brain function in children with DLD. Results from this study provide preliminary evidence of a relationship between altered brain function in children with DLD and language impairments. However, Chapter 3 utilized standardized measures of language abilities, which may not capture nuanced differences in real-time language processing. To address this, Chapter 4 employs an online priming paradigm to investigate real-time syntactic dependency linking in children with DLD at regular and slow rates of speech. Results show that children with DLD possess intact linguistic knowledge, but real-time temporal constraints during sentence processing lead to comprehension breakdowns. These studies provide evidence of the impact of altered brain function on language comprehension in language-impaired populations and illustrate the importance of properly characterizing the neural underpinnings of language processing.