Behavioural and Neural Correlates of Individual Differences in Episodic Memory

Episodic autobiographical memory (AM) refers to the real-life recollection of personal events that are contextually-bound to a particular time and place. Anecdotally, individuals differ widely in their ability to remember these types of experiences, yet little cognitive neuroscience research exists to support this idea. By contrast, there is a growing body of literature demonstrating that individual differences in episodic memory for laboratory experiences, intended to serve as a proxy for real life, are associated with brain-biomarkers. The present studies provide a starting point for exploring individual differences in the real-life expression of memory; which is more complex, multifaceted and has longer retention intervals, than laboratory memory (LM), thus allowing for the assessment of remote memory. While there are many factors that contribute to individual differences in episodic AM, the focus of this dissertation is on genetic influences. In particular, the KIBRA gene has been associated with episodic LM in a replicated genome-wide association study; T-carriers showing enhanced performance relative to individuals who lack this allele. The present series of studies explored the association of KIBRA with episodic AM. An ancillary goal was to clarify the association between KIBRA and episodic LM. Accordingly, in Chapter 2, episodic LM and AM were probed in a large sample of healthy adults in relation to KIBRA genotype. Next, in a subset of participants, functional and structural magnetic resonance imaging (MRI) were used to explore KIBRA-dependent differences in hippocampal and medial temporal lobe (MTL) blood-oxygen-level-dependent (BOLD) response (Chapter 3) and structure (Chapter 4). Akin to prior research, Chapter 2 showed that KIBRA is associated with episodic LM, albeit not on all measures. Moreover, a KIBRA association was observed for remote aspects of episodic AM on some measures. Chapter 3 showed mainly greater hippocampal and MTL cortex BOLD response in T-carriers relative to non-carriers during the recollection of both LM and AM. Moreover, during episodic AM, T-carriers showed a distinct pattern of hippocampal-neocortical connectivity. Finally, Chapter 4 showed that T-carriers have a larger cornu ammonis and dentate gyrus relative to non-carriers, suggesting a potential neural locus for the effects of KIBRA on episodic memory.Ph