Lifestyle factors and neuroimaging metrics as predictors of cognitive performance in healthy aging

Abstract

Despite all the advances made in health-related and psychological sciences, advancing age continues to be accompanied by cognitive decline. Aging is usually associated with major changes in the structure and functioning of the brain that lead to impairments in multiple cognitive functions. The trajectories of age-related effects on the brain and cognition exhibit considerable differences across cognitive domains and across individuals, and investigating approaches and factors that might prevent brain and cognitive decline during aging is considered a topic of great scientific and public health relevance. The overall goal of this thesis was to evaluate age-related differences in brain structure and functional connectivity to further our understanding of the neural mechanisms involved in age-related declines in cognition. This thesis also aimed to investigate the influence of lifestyle factors on age differences in cognition, and in that regard, I focused on the effects of sleep quality and physical activity on memory. In Study 1, I assessed the impact of aging on grey matter volume of the medial temporal lobe MTL and prefrontal cortex PFC and compared the relative contributions of MTL and PFC structures to age differences in associative memory. My findings emphasize the critical role of the frontal lobes, and the control processes they subserve, in determining the detrimental effects of age on memory. Additionally, I observed that the relationship between frontal grey matter volume and memory was not moderated by age or sex, suggesting that greater volume in PFC structures relates to better memory performance across the lifespan and in both sexes. In Study 2, I assessed the effects of age on functional brain networks. Given the essential role of the arousal system (ARAS) in cortical activation and previous findings of disrupted ARAS functioning with age, I investigated the hypothesis that age-related changes in ARAS-cortical functional connectivity may contribute to commonly observed age-related differences in cortical connectivity. The findings of this study showed that the arousal system is functionally connected to widespread cortical regions and suggest that age differences in functional connectivity within the cortex may be driven by age-related changes in the brainstem and these altered connectivity patterns have important implications for cognitive health. In Study 3, I investigated the relationship between sleep quality, physical activity, and memory in middle-age and older adults, in addition to assessing the impact of the COVID-19 pandemic on participants’ mood and sleep quality. Our results showed that people who were more active reported better sleep quality and showed better memory, and better sleep quality was associated with better memory. Moreover, our findings also showed that some of the beneficial effects of physical activity on cognition are partially mediated by improved sleep. Additionally, this study indicated that the COVID-19 pandemic had a deleterious effect on people’s sleep quality and overall well-being. Taken together, these studies suggest that aging is associated with disruptive effects on brain structure and function, and that these changes are associated with age-related cognitive decline. Additionally, our study supported the association between lifestyle factors, more specifically, sleep quality and physical activity, and cognitive performance during aging.