Identifying Factors Underlying Resilience to Age-Related Cognitive Decline

Abstract

Across both healthy and pathological aging, episodic memory abilities can exhibit early declines. Evidence suggests that distinct components of episodic memory retrieval may be differentially impacted by age. In particular, the precision of memories shows detectable declines as early as midlife, whereas the ability to successfully retrieve memories is less sensitive to age. There is substantial individual variability in how memory changes with age, with some individuals maintaining high memory abilities into later life. Engagement in enriching lifestyle activities throughout the lifespan is thought to contribute to the development of cognitive reserve which protects against the effects of detrimental age-related brain changes on cognitive performance. The research reported in this thesis uses a sensitive episodic memory task to detect relationships between lifestyle and memory in contexts where this relationship may be quite subtle. I began by developing an online version of the episodic memory task to extend the usage of the task to contexts where in-person testing was not suitable. In Chapter 3, I describe a behavioural experiment where I compare the performance of younger adults who either completed the memory task in person or online, finding no significant differences in memory performance between testing environments. Capitalising on this validation, in the next two chapters (chapters 4 and 5), I used the online version of the episodic memory task to address the thesis aim of assessing subtle lifestyle-memory relationships. In Chapter 4, this involved investigating the impact of the COVID-19 pandemic which led to unprecedented restrictions on lifestyle activities that have been linked to cognitive reserve. In this experiment, I assessed the impact of lifestyle change during the pandemic on the memory abilities of older adults. This experiment was made possible by the development of the online task so that the memory performance of older adults could be assessed during the pandemic in March 2021 and compared with their performance prior to the pandemic when they completed the memory task in person. In Chapter 5, I describe a behavioural experiment which assessed the contributions of lifestyle activities undertaken both in youth and midlife on memory performance during midlife, when cognitive decline due to age and age-related conditions first begins to emerge. This chapter extends the central aim of the thesis to ask firstly whether there is a critical period during the lifespan when cognitive reserve building activities are particularly effective and secondly whether there is a particular lifestyle type which is most beneficial for maintaining cognitive abilities beyond midlife. In the second part of this thesis, I aimed to examine the mechanisms underlying the relationship between cognitive reserve building activities and episodic memory retrieval using an EEG approach. Neural activity was assessed both during the completion of the episodic memory task (Chapter 6) and while the participant was at rest (Chapter 7). Furthermore, I assessed whether patterns of neural activity, linked to cognitive reserve, moderated the relationship between measures of brain health and cognitive ability in line with rigorous definitions of cognitive reserve. Together, the experiments in this thesis aim to shed light on the use of sensitive cognitive tasks and measures of neural activity to detect relationships between lifestyle and age-related cognitive resilience in contexts where these effects may be more subtle. This includes during the COVID-19 pandemic, a period of unprecedented lifestyle restrictions, as well as in midlife when age-related cognitive declines first begin to emerge. The implications of these findings for understanding the mechanisms underlying lifestyle effects on episodic memory are discussed.