Ageing, cognition and quality of life in autism spectrum disorder: cross-sectional and longitudinal studies

Few studies to date have included older autistic adults, meaning that lifespan outcomes for autistic adults are poorly understood. In this thesis, findings are presented from a four-year programme of research, which followed-up younger and older adults (aged 18-80 years) with a diagnosis of Autism Spectrum Disorder and comparison groups of younger and older typically ageing adults from the general population. The aim of this research was to understand how growing older affects the cognitive functioning, autistic traits, psychological well-being and quality of life of autistic adults. The work reported here extends the recent but sparse literature on autism and ageing and addresses some of the unanswered questions about the lifespan outcomes for autistic adults as they grow older. Is there a steeper risk of cognitive decline with ageing? Does ageing in autism mirror the trajectories of cognitive change seen in typical ageing? Does the cognitive profile of autistic adults stay the same as they grow older? Previous literature has largely neglected the lifespan outcomes of autistic adults in older age, especially concerning questions on the persistence of mental health difficulties across the adult lifespan, and the degree to which cognitive differences and behavioural difficulties associated with autistic traits affects the quality of life of autistic adults as they grow older. The work presented here involved cross-sectional (Study 1) and longitudinal (Study 2) studies. Here, matched groups of older and younger adults with and without a diagnosis of autism spectrum disorder (ASD) were compared at two time points, T1 and T2, approximately 2.5 years apart. Measures were taken of autistic traits, cognitive functions (intellectual ability, language, memory and EF), mental health (anxiety, depression) and quality of life at both time points. The results showed that, at T1, younger autistic adults demonstrated the patterning of cognitive difficulties that resembled older typically ageing adults. Older autistic adults showed a different profile of age-related cognitive abilities, which may be explained by cognitive resilience developed across the lifespan. Nonetheless, co-existing physical and mental health conditions presented difficulties for more than half the autistic adults and were associated with poorer quality of life and well-being across the lifespan. An exploration of longitudinal change from T1 to T2 revealed no age-related changes in the cognitive profiles of younger and older autistic adults. Nevertheless, mental health difficulties persisted, as did poor quality of life. Then, to better understand the specific factors associated with cognitive functioning in older age, Study 3 extended the above work to Prospective Memory (remembering to remember) – a cognitive process that is among the most sensitive to age-related changes in typical ageing. For the first time, prospective memory was explored in ageing and autism, and its relation to quality of life. Ecologically relevant assessments of prospective memory were carried out in laboratory and naturalistic settings, in six experimental tasks. These tasks were designed to test pro-social and self-relevant motivations in event- and time-based aspects of prospective memory, which differentially draw on executive resources and are known to present difficulties for older typically ageing adults. Older autistic adults performed as well as or better than younger autistic adults across the six tasks, showing no age-related difficulties. By contrast, the older typically ageing adults showed age-related difficulties compared to younger typical adults. These findings replicate the previous literature of prospective memory in typical ageing and extend the limited research of PM in ASD to provide, for the first time, an explanation of the cognitive mechanisms associated with prospective memory and their relation to quality of life. The programme of work just described directly addresses some of the key issues associated with ageing and ASD and identifies areas in which some autistic individuals may require supports across their lifespan.