Active Voice: A Single Session of Exercise Induces Hippocampal Plasticity in Older Adults
By J. Carson Smith, Ph.D., FACSM, and Daniel D. Callow

Memory loss is one of the most common complaints of older adults. Lifestyle interventions, including exercise, are increasingly popular to preserve brain health in older age. While there is ample empirical evidence to support the cognitive benefits of a physically active lifestyle, the neurophysiological mechanisms are difficult to determine conclusively in humans. Over months or years, it may not be possible to disentangle the independent effects of exercise from those attributed to factors such as social interactions and diet. However, if daily exercise accumulates to produce brain benefits over time, then it stands to reason that each session of exercise may produce effects from which these long-term adaptations occur.

Animal studies suggest acute exercise may stimulate neural and vascular growth factors that promote the structural and functional integrity of brain tissue and neural networks. These invasive studies cannot be conducted in people, so we are limited to predominantly self-report or behavioral performance and to non-invasive neuroimaging. Recent advances in brain magnetic resonance imaging have been shown to be sensitive to both short-term changes in memory performance and to changes in the structural integrity of the neural networks that control memory.

In our study of healthy older adults, published in the September 2021 issue of Medicine & Science in Sports & Exercise, we performed diffusion tensor imaging after 30 minutes of moderate-intensity aerobic exercise and seated rest. Diffusion tensor imaging is sensitive to the pattern of diffusion of water molecules. The integrity of underlying brain tissue, beyond simply the volume of tissue present, is inferred based on the microstructural properties of the tissue and its impact on water diffusion. We focused on the hippocampus, a brain region critical for memory that is also highly susceptible to neurodegenerative diseases but also benefits from exercise training programs. Interestingly, we found that hippocampal diffusion was elevated following the acute bout of exercise as compared to seated rest; an effect not observed in a whole-brain average or in other control regions.

Based on observations in rodent models, we hypothesized that elevated diffusion in the hippocampus may be associated with increased neuroinflammation and glial activity in the hippocampus. While increased hippocampal inflammation might seem counterintuitive or even detrimental to brain function, this may not necessarily be the case. Chronic levels of neuroinflammation do increase in older age and with poor lifestyle choices, which are associated with poor health outcomes and disease. However, acute inflammation has been shown to upregulate neural growth factors that are beneficial for brain health.

One might think of this like exercise and blood pressure. While high systolic blood pressure is generally considered a sign of poor health, high blood pressure is necessary and adaptive during and immediately following strenuous exercise. Over time and repeated bouts of exercise, adaptations occur that lower resting blood pressure, improving overall cardiovascular health. It is possible that similar adaptations to the stress of exercise occur in the hippocampus.

These findings support the premise that a single session of exercise is like a dose of medicine for the brain, and further substantiates the view that a physically active lifestyle promotes brain health in older adults.

About the authors:
J. Carson Smith, Ph.D., FACSM, is a professor in the Department of Kinesiology and the Neuroscience and Cognitive Science doctoral program at the University of Maryland in College Park. Dr. Smith has been an ACSM member for more than 25 years, and he currently serves on the Strategic Health Initiatives on Aging.

Daniel Callow is a graduate student member of ACSM and is currently completing his doctoral degree in Neuroscience and Cognitive Science at the University of Maryland.

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily represent positions or policies of ACSM. Active Voice authors who have received financial or other considerations from a commercial entity associated with their topic must disclose such relationships at the time they accept an invitation to write for SMB.