Aging is often associated with a progressive decline of cognitive functions, due in part to the susceptibility of specific brain regions to stressors of aging. However, chronological age is a poor predictor of cognition. Cognitive decline is variable in terms of onset and progression, suggesting that biological age, due to differences in biological mechanisms that regulate vulnerability, is a better predictor of cognitive decline. As with humans, animal models exhibit variability in age-related cognitive decline, and this variability has been employed to determine biomarkers and mechanisms of cognitive impairment. Based on these animal models, theories of age-related cognitive decline have evolved. Recent work has focused on senescent physiology, rather than cell death associated with neurodegenerative disease. The results suggest that age-related alterations in redox stress modify Ca2+ regulation to alter learning and memory mechanisms, as well as signaling cascades from the synapse to the nucleus. Furthermore, the stressors of aging, senescent physiology, and environmental factors interact with epigenetic mechanisms contributing variability in gene transcription, resulting in variability in resiliency, onset, and the progression of the aging phenotype.

Declines in cognitive functioning are a normal and widespread consequence of normal aging. Lacking promising drug interventions for reducing cognitive deficits, the field of cognitive aging has turned to nonpharmacologic treatments that could prevent or delay cognitive decline, or even improve performance in those at risk for decline. Physical activity is one of the most promising behavioral approaches for influencing cognitive and brain health. In this chapter, we first describe the ways of studying the relationship between physical activity, cardiorespiratory fitness, and cognitive functioning. We then summarize the existing evidence for how physical activity and cardiorespiratory fitness influence both cognition and the brain in the context of aging. By the end of the chapter, readers should be able to describe (1) typical patterns of associations between physical activity, cardiorespiratory fitness, and cognitive and brain health in older adults; (2) the evidence that increasing physical activity improves cognitive functioning in older adults; and (3) whether physical activity influences cognitive functions and brain health in older adults with mild to more severe cognitive deficits, such as found in people with mild cognitive impairment or dementia.

It is frequently reported that processing speed slows and executive functions (EFs) become less effective in the course of healthy aging. This chapter highlights research supporting these claims in three areas of investigation: cognitive aging research, the neuropsychological perspective, and studies evaluating the association of EF with structural and functional imaging measures. Several themes emerge in this review. For example, diminished processing speed with aging appears to reflect aging-related changes in the anterior cingulate/superior medial frontal cortex, as well as perceptuomotor slowing. The definition of EF varies between different publications and there is a need for more precise operational definitions. There is also a need to decompose EFs into their component processes. Impairments of EF are strongly related to damage in prefrontal regions, but disorders of EF also occur with injury to nonfrontal regions, indicating that complex networks are involved in EF. Additionally, domain-specific changes beyond the changes in EF are important considerations in network analyses. We propose a method to advance future research on EF by using focal frontal lesion studies and neural network principles as frameworks to expand our understanding of aging-related changes in EF and processing speed.