Aging is associated with a heterogeneous pattern of structural and functional brain changes, as well as an increased risk of clinical conditions like stroke with subsequent cognitive and functional impairments. Epidemiological studies have documented prolonged life expectancy with an increasing number of older adults and an increasing number of stroke survivors. Hence, it is highly prioritized to identifying protective factors with the potential to slow down brain aging, delay more severe changes and associated diseases, and enhance brain and cognitive health for patients with neurological disorders. Previous research suggests that maintaining a high level of activity and physical functioning in everyday life is associated with advantageous brain and cognitive health. However, research findings on this matter have been inconsistent. Methodological developments in clinical and cognitive neuroscience, and advanced brain imaging using magnetic resonance imaging (MRI), have provided opportunities to better understand this area of research.
The overarching aim of this thesis is to investigate how everyday living and functioning, including level of activity, participation, and physical function, are associated with normative brain aging and post-stroke cognitive training results. In the three separate papers constituting this thesis, a combination of cross-sectional and longitudinal data (mean interval 506 days) from both healthy participants and stroke survivors in the chronic phase was used. The latter group completed an additional computerized cognitive training intervention (CCT) aimed at improving working memory.
Briefly, in Paper I, a cross-sectional design was used to examine associations between daily physical activity level or physical function (hand-grip strength, walking speed and balance), and structural brain imaging features in older adults. The structure of the brain allows for a swift flow of information across the entire nervous system. Age and diseaseinduced changes can disrupt these processes, causing cognitive and behavioral difficulties. Two MRI sequences were used, obtained from 122 adults aged 65-88 years: global white matter fractional anisotropy (FA) and mean diffusivity (MD) from diffusion tensor imaging (DTI), and brain age prediction using brain morphometry measures from T1-weighted imaging data. The results indicated an association between higher number of daily steps and lower estimated subcortical brain age, compared to chronological age, in females. This indicates a “younger” appearing subcortical structural brain in more active individuals. Furthermore, the results supported an association between higher comfortable gait speed and higher global white matter FA.
In Paper II, the association between level of activity and participation, and MRI arterial spin labelling-derived cerebral blood flow (CBF) was investigated. CBF is critical for maintaining brain metabolism and is vulnerable to age-related changes. The latter has been linked to neurocognitive disorders and vascular events. Cross-sectional and longitudinal data were obtained from 118 adults aged 65-89 years at baseline and 86 adults aged 66-86 years at follow-up. Cross-sectional analysis indicated that higher CBF in both cortical and subcortical regions was associated with higher levels of low and moderate-to-vigorous intensity physical activity, social activity, and reading. Anecdotal evidence supported associations between more stable regional CBF and more reading and gardening.
In Paper III, the link between physical activity of different intensities and both cognitive performance and response to a computerized cognitive intervention for stroke patients in the chronic phase was investigated. To promote cognitive function in individuals’ post-stroke, it is essential to have effective interventions and an understanding of factors that could influence the rehabilitation outcome. Longitudinal data from 52 stroke-survivors with a mean age of 70 years was included. The results demonstrated no evidence of more physical activity or less sedentary behavior resulting in better performance or response to CCT. However, more minute’s sitting was associated with better performance.
In sum, the papers described in the current thesis show that engagement in more everyday activities, both physical, cognitive, and social, and maintaining better physical function may reflect better structural brain health and healthier regional cerebral blood flow in elderlies. However, the analysis revealed indecisive support for level of activity and participation being protectors against longitudinal reduction in CBF, nor was engagement in more physical activity shown to be a central component in post-stroke cognitive training response. Future studies can benefit from investigating the main topic of this thesis in populations with a wider variation of activity level, health status, education, stroke severity, and functional limitations. Further research on how everyday living and functioning may alter brain- and cognitive health can lead us towards effective approaches to maintaining and promoting brain health in both normative and clinical populations.