Fitness Helps Brain Function As We Age

Brain Function

Julia Basso , PhD

Affiliation: Post-doctoral Research Associate, New York University, Center for Neural Science

For the past 40 years, the world’s leading experts on learning and memory have gathered in Park City, Utah to discuss the newest and most exciting research on brain function: the brain’s ability to learn and remember information.  I recently attended this year’s conference, which hosted the first ever panel on “Current Topics in the Neurobiology of Exercise and the Brain”. 

Speakers included Monika Fleshner who gave a talk on early life exercise and the gut microbiota as well as Henriette Van Praag who discussed how running alters the structure and function of a brain region known as the dentate gyrus (where adult neurogenesis occurs).  Another speaker, Michelle Voss, Assistant Professor at the University of Iowa, talked about the relationship between physical activity and fitness with functional brain health in older adults.  Importantly, she emphasized a major missing hole in the literature.  That is, we do not understand how physical activity “protects the brain from the adverse effects of aging.”  Subsequently, this leads to the problem of not knowing how to prescribe the right exercise regimen for aging.  Voss and her colleagues recently conducted research to address these issues.

Cardiorespiratory Fitness and Brain Function

Research has shown a significant relationship between cardiorespiratory fitness (VO2 max) and brain health.  Specifically, individuals who are more fit tend to have healthier brain structure (greater brain volume). They also have higher levels of cognitive functioning, and less risk of cognitive decline and dementia-related death [1, 2]. However, not all studies have found this association [3].  However, fitness level is not necessarily a direct physiological correlate of the amount of physical activity you engage in.  Cardiopulmonary fitness, for example, is strongly affected by genetics, which may account for approximately 50% of the variance in individual fitness levels [4].  Therefore, a more holistic and perhaps better way to assess the influence of exercise on brain health is to examine cardiopulmonary fitness in conjunction with specific features of the physically active lifestyle.

One way to examine brain function is to image the brain using functional magnetic resonance imaging (fMRI).  Through this technique, scientists can visualize which brain regions are active either during a specific cognitive task or at rest.  One measure that can be assessed with fMRI is resting-state functional connectivity, a measure of brain regions that are active together during rest. 

Fitness Helps Brain Function As We Age

Brain Networks and Connectivity

Collectively, these brain regions form networks. Networks such as the default mode network, which includes areas of the hippocampus and prefrontal cortex. This area is thought to be involved in internal thinking such as daydreaming, mind-wandering, and remembering the past or planning the future.  Researchers have shown that the integrity of these networks predict age-related decline in brain function [5]. Voss and her colleagues decided to consider the connection between aging, brain health, and fitness. Consequently, they conducted a study to test whether in comparison to healthy, young adults, older adults would display significantly greater disruption in several brain networks. Furthermore, they wanted to see whether fitness and physical activity would most strongly predict functional connectivity in the networks most strongly affected by age-related changes.

In order to test these hypotheses, 189 healthy older adults (65.1±4.4 years of age) and 36 healthy, young adults (22.1±3.0 years of age) had their brains imaged with MRI while laying still with their eyes closed [6].  Step counts via a wearable accelerometer assessed physical activity. A standard VO2 max test assessed physical fitness.

Findings

As a result, this study produced several significant findings.  First, there are three brain systems that are highly sensitive to aging:  the default mode network, the executive control network, and the salience network.  These networks aid a variety of behavioral processes but are primarily associated with cognitive functioning.  Second, the deterioration of these networks does not necessarily seem to be an inevitable facet of aging.  Third, cardiopulmonary fitness moderates the integrity of these networks, especially in the frontal as well as temporal cortices. These are key areas involved in learning and memory. 

Excitingly, these results suggest the functional networks that are most sensitive to age-related decline also appear to be the most sensitive to fitness and exercise training [7, 8].  Importantly, fitness rather than physical activity level is the key to explain the relationship between exercise and brain function and health.  Therefore, it is important that when choosing a physical activity, try engaging in an exercise that significantly increases your heart rate. This leads to increases in aerobic fitness over time.  For example, high-intensity interval training is an excellent choice. This workout regimen has been shown to be one of the fastest and most efficient ways to increase cardiopulmonary fitness. Consequently, future research will be needed to examine whether training regiments such as high-intensity interval training are the best way to prevent age-related decline in brain function.

References:

1. Angevaren, M., et al., Physical activity and enhanced fitness to improve cognitive function in older people without known cognitive impairment. Cochrane Database Syst Rev, 2008(3): p. CD005381.

2. Smith, P.J., Physical activity, vascular health, and cognitive impairment. Arch Intern Med, 2012. 172(1): p. 83; author reply 84.

3. Smiley-Oyen, A.L., et al., Exercise, fitness, and neurocognitive function in older adults: the “selective improvement” and “cardiovascular fitness” hypotheses. Ann Behav Med, 2008. 36(3): p. 280-91.

4. Bouchard, C., et al., Genomic predictors of the maximal O(2) uptake response to standardized exercise training programs. J Appl Physiol (1985), 2011. 110(5): p. 1160-70.

5. Dennis, E.L. and P.M. Thompson, Functional brain connectivity using fMRI in aging and Alzheimer’s disease. Neuropsychol Rev, 2014. 24(1): p. 49-62.

6. Voss, M.W., et al., Fitness, but not physical activity, is related to functional integrity of brain networks associated with aging. Neuroimage, 2015.

7. Voss, M.W., et al., Functional connectivity: a source of variance in the association between cardiorespiratory fitness and cognition? Neuropsychologia, 2010. 48(5): p. 1394-406.

8. Voss, M.W., et al., Plasticity of brain networks in a randomized intervention trial of exercise training in older adults. Front Aging Neurosci, 2010. 2.

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