Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Psychology

Supervisor

Joanisse, Marc F.

Abstract

This thesis investigated associations between the white matter connectome and reading in children with a wide range of reading abilities. It is well established that the connectome supports the interplay among brain regions and connections within an integrated system. In this dissertation, I examine the hypothesis that it could therefore represent multiple mapping processes among reading components and further explain variations in reading performance. Such associations between the organization of the connectome and reading skills have not been well explored. This thesis aimed to address this issue by considering both the relationship between connectome measures and standardized reading performance out of scanner, and neural activations during in-scanner reading tasks. Chapter 2 examined the rich-club organization of the white matter connectome and its association with sight word reading, phonemic decoding, reading comprehension, and rapid automatized naming in children. I found that feeder connections that link hub and reading network regions were associated with word-level reading skills. Chapter 3 further examined how the left thalamus influences reading skills by coordinating information flow between the reading network and hub regions. Results showed that the efficiency metrics and routing cost of the left thalamus within a subnetwork, which contains the reading network and hub regions, were associated with rapid automatized naming and phonemic decoding scores, respectively. Chapter 4 applied network control theory to investigate if the white matter connectome could explain the dynamics of functional activation. Specifically, I examined if control energy, which reflects the level of cognitive demands from a task, showed differences across different conditions of an in-scanner rhyming task. I found that conditions requiring more effort were associated with higher control energy within reading network areas. In addition, the control energy of the superior temporal gyrus and fusiform gyrus showed dissociations regarding different modalities of stimulus presentation. Moreover, children with better word-level reading scores required lower control energy. Chapter 5 summarizes the findings and discusses their implications to the connectome-reading relationship.

Summary for Lay Audience

Reading is a complex skill. It requires fluent integration of multiple aspects of information, including visual inputs about letters and words, pronunciation of those inputs, and conceptual knowledge supporting the understanding of reading materials. Prior neuroimaging studies identified brain areas and connections responsible for processing or mapping specific aspects of information, revealing a leftward lateralized reading network in the brain. However, these findings provide limited neural evidence describing how those isolated processes interact with each other to support reading as a continuous and integrated process. This thesis applied the connectome framework to view the brain as an interactive network, which contains information about interplays among brain areas and connections within the reading network and the entire brain. Therefore, this thesis was designed to explore the role of network features in supporting different reading subskills in school-aged children.

The first study in this thesis explored how the center-located hub regions in the white matter network and their connections were associated with reading skills in children. This study found that connections between hubs and the reading network supported pronounceable non-word reading skill. The second study further explored the role of the left thalamus, the overlapped area between hubs and reading network, in coordinating communication between the two subnetworks and its association with reading subskills. The results showed that the thalamus supported different reading subskills by coordinating communication in distinct ways. On top of behavioral reading subskills, my third study examined if the white matter connectome could explain functional activation changes in the brain when children were doing reading tasks. By applying the network control theory, this study identified that the reading network areas should be more engaged when the task requires more cognitive loads. Overall, this thesis extends our understanding of the contribution of the brain in supporting reading from individual brain structures to the network system.

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