PhD Oral Exam - Paul-Noel Rousseau, Psychology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Long regarded as being uniquely involved with motor control, the cerebellum is now recognized to contribute to nearly every aspect of human cognition. The cerebellum forms reciprocal connections with much of the cerebral cortex, receiving input via the pons and sending output back through the deep cerebellar nuclei and thalamus. These topographically organized, closed loop circuits, are thought to underly the cerebellum’s capacity to influence such a breadth of different processes. These connections have a rich history of study in non-human animals, but their organization in humans is largely understudied. In this dissertation we present a series of three studies that investigated the connectivity of the downstream, cortico-ponto-cerebellar, pathway in humans. In our first study (Chapter 2) we reconstructed connections between the pons and lobules of the cerebellar cortex using diffusion MRI tractography. We demonstrated topographic organizational principles broadly reflecting the segregation of motor and non-motor inputs to the cerebellum. Our second diffusion MRI tractography study (Chapter 3) mapped the corticopontine segment using methods to reconstruct gradients that reflect the continuous mappings of the cerebral cortex onto pons. In our final study (Chapter 3), we shifted to a functional connectivity approach, reconstructing gradients in the pons based on its connectivity with the cerebral and cerebellar cortices. While the first two studies serve as bridges to prior work conducted in non-human animals, the final study supports a novel perspective of the pons as a functionally dynamic integrative hub. Taken together, this work advances our understanding of cerebellar connectivity in humans and, by extension, its diverse contributions to behaviour and cognition.