Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Neuroscience

Supervisor

Duerden, Emma

2nd Supervisor

De Ribaupierre, Sandrine

Co-Supervisor

Abstract

The third trimester of gestation is scarcely studied despite this being a key window for the development of learning and memory systems. In a prospective cohort study, 30 pregnant women participated in one or two fetal MR imaging sessions between 28- and 39 weeks of gestational age. Activation time courses were extracted from the default mode (DMN), medial temporal lobe (MTL), and thalamocortical (TCN) networks of the fetal brain. Generalized estimating equations were used to examine the association between the DMN-MTL, DMN-TCV connectivity strength, and subcortical volumes. Increased functional connectivity strength between the DMN-MTL networks was negatively associated with smaller hippocampal volumes. In contrast, increased functional connectivity strength in DMN-TCN was associated with smaller thalamic volumes. No associations between DMN connectivity strength were seen with cerebellar volumes. These associations indicate the emergence of strong short-range connectivity in the third trimester. Developing fetal MRI biomarkers facilitates the formation of a normative model of brain networks involved in cognitive processes.

Summary for Lay Audience

The functional and structural formation of brain networks during the gestational period supports the development of learning and memory systems. These brain networks are present while the brain is at rest and start to develop in the fetal brain starting in the second trimester of pregnancy. Critical brain networks are the default mode network (DMN), the medial temporal lobe network (MTL), and the thalamocortical network (TCN) and play a critical role in learning and memory. Disruptions in the maturation of the networks during the fetal period may influence learning and memory difficulties later in life. In turn, better characterization of the networks and how they develop can improve our understanding of healthy brain development and aid in the identification of potential learning and memory difficulties early on in life, particularly in fetuses who may be at risk. This thesis aimed to analyze the association between subcortical structures and the DMN, MTL, and TCN connectivity strength during the third trimester of gestation. To achieve this aim, we acquired fetal magnetic resonance imaging (MRI) data during the third trimester of pregnancy. We obtained the volumes of brain regions involved in learning and memory, including the hippocampus, thalamus, cerebellum, amygdala, and basal ganglia. We also extracted the time courses of activation of the DMN, MTL, and TCN to study the strength of their connectivity. Finally, we performed a statistical analysis to examine the associations of the DMN-MTL, DMN-TCN, and subcortical volume size respectively.

We found negative associations between the hippocampus with the DMN-MTL networks. We also found negative associations between the Thalamus and the DMN-TCN networks. These results suggest that memory networks can be detected during the gestational period and are associated with the size of subcortical structures. Characterizing the development of brain networks in the fetus can aid in studying learning and memory abilities early in life.

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