An Investigation into the Connective Anatomy of the Temporal Lobe using Diffusion Tractography and Parcellation Techniques

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Abstract

The temporal lobe is one of the four main lobes of the brain. It underpins a variety of cognitive functions from the basic processes of audition to the higher level integrative functions of semantic cognition. A fundamental assumption about the workings of the human brain is that function emerges from the interactions between different anatomical neural structures. This thesis is an investigation into the white matter, or connective, anatomy of the temporal lobe with references to the interplay between structure and function. It is a work submitted in the alternative format comprising of eight standalone articles that expand on different aspects of the connectivity of the temporal lobe. The first section of the thesis provides a review of the methods used in this chapter, specifically the processes of diffusion MRI and background on the spectral transformation which is a technique that is used later in the thesis. The second section of this thesis presents a historical and contemporary review of the temporal lobe's anatomy and identifies key areas of interest for the subsequent sections. This section presents the first English translation of the work by Joseph and Augusta Dejerine on the long association fasciculi. The third and fourth sections comprise the empirical work. Section three explores the interface of the temporal lobe to the rest of the brain; the extreme capsule. Using hierarchical clustering, the work identifies novel subcomponents of this region. The work also explores the cognitive functions that are associated with the cortical end point of different tracts within the temporal lobe. The second empirical section focuses on analysing the connective similarity of the temporal lobe and identifying gradients in the similarity structure. This section uses the novel spectral embedding techniques that were discussed in the methodology section. The structural gradients of temporal lobe's connectivity are explored and their functional relevance is discussed. Taken together, the findings in this thesis build a framework within which to think about connectivity in general and in the temporal lobe in particular. Drawing upon both contemporary and historical understanding of white matter the concept of gradations in structural connectivity was introduced. Using novel data-driven techniques the temporal lobe's structural gradients were explored. Institution: The University of Manchester Candidate: Claude Julien Bajada Degree title: Doctor of Philosophy Thesis title: An Investigation into the Connective Anatomy of the Temporal Lobe using Diffusion Tractography and Parcellation Techniques

Keyword(s)

Diffusion MRI; Neuroanatomy; Semantics; Spectral Reorder; Temporal Lobe; Tractography

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