Physical Fitness and Sociocognitive Engagement are Associated with Different Aspects of Cognition in Older Adults

To the Editor: Alzheimer's disease (AD) is characterized by progressive neural decline resulting in severe memory loss that interferes with daily life. One in nine Americans aged 65 and older has AD, and the incidence is projected to increase rapidly as the population ages.1 There is no cure for dementia, and thus there is urgent need to identify interventions that will help older adults maintain cognitive abilities for longer into their life span. Exercise has shown promise in alleviating aspects of age-related cognitive decline,2 but more work is needed to understand how exercise may reduce the risk of dementia and more specifically which aspects of cognition exercise targets. Physical fitness may be mitigating memory loss to delay AD diagnosis, but little is known about the link between physical fitness and memory function in healthy older adults; the main aim of the present study was to examine that relationship. Studies examining the relationship between exercise and memory in healthy older adults have yielded mixed results. In one study, older adults with higher levels of aerobic fitness had better spatial working memory for material tested after a 3-second delay,3 but this is too short a delay to examine long-term memory, which is affected by AD. Improvements in memory for material retained over longer delays have been observed after low-intensity exercise training but not moderate-intensity training,4 suggesting that aerobic fitness benefits resulting from an exercise program may not underlie the memory benefits. Furthermore, one study found no association between self-reported physical activity and episodic memory in older adults; however, participants who reported watching more television had poorer episodic memory,5 suggesting that disengagement from sociocognitive activities may be particularly detrimental for memory in aging. Engaging in socially and cognitively stimulating activities has been shown to mitigate cognitive decline in aging and reduce the risk of AD.6 The present study assessed the relationship between an objective measure of physical fitness7, 8 and performance on multiple cognitive domains: episodic memory (Face–Name Association task; Delayed Match-to-Sample task), processing speed (Simple Reaction Time task), and executive functions (Directed Forgetting task; Number Stroop task; Go/no-go task) in 68 healthy older adults (34 female; mean age 71.8 ± 6.2, range 60–86) recruited from the community. All participants were free from neurocognitive impairment (mean Montreal Cognitive Assessment (MoCA) score 26.4 ± 2.6, range 20–30). It was expected that greater physical fitness would be related to faster processing speed and better executive functions.9 The critical question was whether there would be a positive relationship between memory and fitness. The relationship between cognitive function and physical fitness was also assessed controlling for engagement in sociocognitive and physical activities. Hierarchical multiple linear regression showed that processing speed (Simple Reaction Time) and executive functions (Directed Forgetting) were associated with physical fitness (Table 1). Critically, memory (Face-Name Association; Delayed Match-to-Sample) was not associated, demonstrating that the relationship between physical fitness and cognition is selective. Performance on two different memory tasks was associated with sociocognitive activity, suggesting that these types of lifestyle factors may support aspects of cognition. Executive functions were also associated with sociocognitive activity, and this association was independent of that observed between executive function and physical fitness, indicating possible synergistic benefits of combining aerobic fitness with sociocognitive activities. Processing speed, which had the strongest relationship with physical fitness, was not associated with sociocognitive activities. Physical fitness and sociocognitive activities were not related (correlation coefficient (r) (66) = 0.00, P = .50), suggesting that these lifestyle factors may support overlapping and distinct brain processes. Although physical activity was associated with physical fitness (r(66) = 0.22, P = .04) and sociocognitive engagement (r(66) = 0.33, P = .003), it was not associated with cognition (Table 1). However, this measure of physical activity did not distinguish activity based on its intensity, duration, or sociocognitive engagement, which may be important for understanding how physical activity supports different aspects of cognitive function. Although previous research suggests that physical fitness reduces the risk of AD, the present study found no association between physical fitness and memory function in healthy older adults. Instead, memory function was positively related to sociocognitive activity, suggesting that protection from memory decline with aging may not be directly related to the fitness benefits but rather a product of the sociocognitive activities that may or may not be inherent to exercise programs. Although the present study did not demonstrate a causal relationship, it highlights the need to consider sociocognitive engagement to fully understand the effect of exercise on preserving memory function in aging. Specifically, an exercise program incorporating physical fitness and sociocognitive engagement may have the greatest benefit for cognitive function in healthy older adults in terms of reducing the risk of cognitive impairment. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: Clark, Vandermorris, Heisz: study concept and design, preparation of manuscript. Clark, Heisz: acquisition of subjects and data, analysis and interpretation of data. Sponsor's Role: None.

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