Executive function abilities, cognitive ageing, and cognitive decline

Abstract

Decline in cognitive abilities is a predominant feature of cognitive ageing and neuropathological conditions, which is attributed to the decline of executive functions (EFs). Four EFs are suggested to be particularly important, dual-tasking (DT), inhibition, shifting, and working memory (WM) updating. As part of the research completed in this thesis, two studies sought to determine the age-associated trajectory of decline of these abilities as this has not been extensively researched. An initial literature review (Chapter 2) evaluated how these abilities have previously been examined in cognitively healthy and pathological impaired older adults. A cross-sectional behavioural study (Chapter 3) conducted between young and older adults where each EF was assessed with a pair of tasks, showed age-associated decline in some measures. Results further demonstrated that inhibition, shifting, and updating declined at a comparable high rate, whereas DT declined independently at a lower rate. A following correlation analysis (Chapter 4) between task pair measures of each EF in both age groups, found a significant positive correlation in DT in the older adults. Confirmatory factor analysis (Chapter 4) of these task measures revealed the older adults showed a better common EF factor loading than the young adults. Furthermore, correlation loading analysis between the EFs showed a weakly correlated four-factor model in the young adults, and three- and two-factor models in the older adults, indicating age-related structural change of EFs due to dedifferentiation (Koen & Rugg, 2019; La Fleur et al., 2018). Lastly, a voxel-based morphometry study (Chapter 6), using secondary imaging data from the OASIS-3 database (LaMontagne et al., 2019) of participants ranging from cognitive healthy to advance Alzheimer’s disease, identified substantial atrophy in the medial temporal lobes but not in the prefrontal cortex, the region primarily associated with EF processing. Nevertheless, atrophy in midbrain structures which are important for EF processing seemed to be associated with performance in the EF tasks employed. The findings of this thesis illustrate that cognitive ageing is not a unitary process, therefore, further research into how the trajectory of the four EFs differs in neuropathological conditions would aid in understanding cognitive impairment greatly.