The relationship between connectome structure and cognition

Abstract

Cognition consists of many abilities, designed to allow the animal to interact effectively with the environment. In this thesis, we explore the relationship between cognition and the network of connections within the brain, known as the connectome. Firstly, we assess the spatial organisation of the macaque monkey connectome. We ask whether regions are arranged so as to minimise the total wiring length, a theory known as component placement optimisation. We find that the total wiring length of the connectome can be reduced by repositioning brain regions, suggesting the presence of alternative constraints on brain connectivity. We subsequently construct a model of neural dynamics to obtain a mechanistic understanding for why the brain is sub-optimally arranged with respect to its wiring configuration. Next, we explore spatial optimisation in the human connectome. We find that the human connectome can be spatially rearranged to reduce the total length of all connections, and that regions differ in their contribution towards this reduction. We find evidence to suggest that this sub-optimal spatial arrangement of brain regions supports healthy dynamics by encouraging greater fluctuations in global synchrony throughout the brain. We also explore connectome structure in the context of impaired cognition, specifically in subjects with schizophrenia, where we identify a link between symptom severity and the spatial organisation of the frontal lobe. Lastly, we investigate the relationship between connectome structure and intelligence, performing numerous spatial and topological analyses on the human connectome alongside measures of fluid and crystallised ability. We find evidence suggesting that fluid ability, rather than crystallised, is linked to spatial features of the connectome, and, in particular, with connectivity that is closer to being spatially optimised. Our work contributes towards an understanding of the spatial and topological features of the connectome, and offers novel insights into the mechanisms that underpin cognition