Exercise and the Brain

Animal Studies

An emerging literature has documented the benefits of physical activity on brain and cognitive function. This research has been prompted, in part, by animal studies, which report that running influences brain function on at least three different levels. First, rodent studies have shown that wheel running accelerates learning rates. In tasks such as the Morris water maze and other hippocampal-dependent spatial tasks, exercising rodents perform better than their sedentary counterparts. Second, exercising animals show robust differences in brain morphology [Page 327]compared to sedentary controls. Exercise induces neurogenesis, or the proliferation and survival of new neurons, and angiogenesis, or the proliferation of new capillaries. Although the functional significance of neurogenesis remains controversial, behavioral performance improvements associated with exercise suggest that newborn cells might facilitate learning and memory. Finally, exercise enhances levels of important molecules in the brain, including neurotransmitters and neurotrophic factors.

For example, exercise increases the production and secretion of molecules promoting the formation of new blood vessels such as insulin-like growth factor and vascular endothelial growth factor. Brain-derived neurotrophic factor is also upregulated with exercise treatments and is necessary for long-term potentiation, a neural analog of long-term memory formation, and for the growth and survival of new neurons.

Human Studies

In humans, the effect of exercise on brain and cognitive function tells a similar story. Three types of experimental designs have been used to test this relationship: prospective-epidemiological, cross-sectional, and randomized trials. A review of the epidemiological literature suggests a significant relationship between physical activity and cognitive function in late adulthood. In a typical study, men and women are asked to report the number of times per week that they perform different aerobic, or physical, activities. These individuals are then followed for 5 to 10 years and the risk for disease is examined in relation to the frequency of self-reported physical activities. These studies have found that the incidence rate for Alzheimer's disease and other neurological diseases is significantly higher for individuals who are infrequent exercisers compared to those who exercise more frequently.

Epidemiological studies have provided intriguing support for the relationship between physical activity and neurocognitive function. However, such studies cannot establish causal links between these constructs. Over the past several years, there have been a relatively small but increasing number of randomized trials in which relatively sedentary individuals, often over the age of 60, are randomized to an aerobic training group (i.e., walking, swimming, bicycling) and a control group that often entails nonaerobic activity such as toning and stretching. Training is usually conducted for an hour a day for several days a week and can last several months. Cognition, and sometimes brain function and structure, is examined prior to and subsequent to the intervention.

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