Structures and Connections of the Ccerebral Cortex in Diprotodontid Marsupials and Comparison with Eutherians

Abstract

This thesis focuses on variation in cortical structure across diprotodontid marsupials and aims to elucidate the archetypal features of the mammalian cortex and those transformations that are of evolutionary importance. The study analysed these features both qualitatively, quantitatively and also compared MRI and DTI derived connectome reconstructions in representatives of the major families of diprotodontids with a representative eutherian (the laboratory mouse). Overall findings suggest that a number of features of the cerebral cortex are retained in all the species examined and have been conserved throughout mammalian evolution and likely represent key aspects of neocortical organization. The differnces observed may be solutions to environmental challenges. For example, a different scaling relationship of hippocampal volume against brain volume has been found amongst the diprotodontids and eutherians. Very small-brained diprotodontids have quite small hippocampal formation volume for their brain size, but the hippocampal formation size increases more steeply with brain size amongst diprotodontids compared to eutherians. The role of the hippocampus in spatial cognition is of direct significance to home range and in species where social behaviour plays an important role, the involvement of the hippocampus in social information processing is also of ecological significance.