Sleep and memory in normal ageing and pre-clinical Alzheimer’s disease

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy (Psychology) to the Department of Psychology and Counselling, School of Psychology and Public Health, College of Science, Health and Engineering, La Trobe University, Bundoora.

The public version of this thesis does not contain all material submitted for examination.

Sleep disturbance is increasingly recognised as a potential early marker or risk factor for emerging Alzheimer’s disease (AD). As sleep is known to be associated with memory, and memory impairment is typically one of the earliest features of AD, understanding the relationship between sleep and memory in the preclinical stages of AD will be highly informative. Currently, there is limited literature examining sleep and memory in ageing, and the preclinical stages of AD, such as subjective memory decline (SMD) and amnestic mild cognitive impairment (aMCI). Therefore, the aims of this thesis were to i) examine the relationship between sleep and memory in healthy ageing to first establish a normative model (Study 1); and ii) examine the relationship between sleep and preclinical AD, including SMD (Study 2), and aMCI (Study 3). The findings demonstrate an association between sleep and memory in normal ageing, whereby objective indices of habitual sleeping patterns predicted memory performance. In people with high levels of SMD, better sleep quality was observed, contrary to expectation. This was interpreted as a possible compensatory mechanism. In contrast, there was evidence of sleep disturbance in aMCI, despite being measured in naturalistic settings, using in-home sleep monitoring (actigraphy and polysomnogaphy). Interestingly, on two non-consecutive nights of polysomnogaphy, there were differential improvements in aspects of sleep architecture between aMCI and control groups, some of which were associated with better overnight memory retention of material. The findings highlight the importance of sleep for memory function in healthy ageing and possible emerging neurodegenerative disease. The capacity of sleep systems to adapt to health challenges reinforces the notion of sleep as a target for memory intervention in ageing populations at risk of cognitive decline.