Fractional anisotropy in frontotemporal association tracts is related to spatial aspects of episodic memory performance: a dMRI study

Abstract

The representation of time and space in the human brain reflects intuitive, yet complex dimensions that are difficultly measured. The study of spatial representation in the brain is perhaps most commonly associated with grid cells, place cells and head direction cells, and recently, time cells have also been isolated in rodents. Spatial cognition is not one single ability, but consists of a myriad of processes, probably extending to include temporal scaling as well. This likely implicates episodic memory functions. In this study I examined several episodic object-related tasks in which a model of retrospective events was required. I wished to investigate whether individual differences in white matter fractional anisotropy (FA) could explain differences in the spatial and temporal recall abilities in a set of healthy, young adult males, and I also attempted to find out if there was an association between cerebellar white matter volume and test performance. The software TRACULA (TRActs Constrained by UnderLying Anatomy) was used for magnetic resonance tomography based reconstruction of white matter tracts from diffusion-weighted images, and mixed linear models were fitted for investigating associations between FA and levels of spatial and temporal memory performance. The probabilistic tractography demonstrated that FA in fronto-temporal tracts was associated with test performance, particularly in the inferior longitudinal fasciculus (ILF) and uncinate fasciculus (UNC). The results presented in this thesis show that spatial aspects of episodic memory, as investigated in virtual reality environments, are related to white matter integrity, operationalized as fractional anisotropy.