Exercise Comes of Age: Brain Training

Abstract

Dementia is a growing global concern engendering immense societal cost and personal suffering. It is the leading cause of dependence and disability in the older population in Australia, as it is worldwide. Prevention is critical to interrupt the spiral of physical, emotional, and cognitive suffering globally as the demographic shifts continue to expand this epidemic. Decades of research into pharmacological treatments to either prevent or treat dementia in healthy adults or those with memory loss have not been successful, and thus recent attention has turned to lifestyle and risk factor reduction. Notably, robust animal and epidemiological data strongly support the role of physical exercise in modifying brain structure and cognitive performance across the lifespan. For example, in prospective studies higher self-reported physical activity is associated with a 20–30 % reduction in incident dementia, while objective measurement of total activity-related energy expenditure has been linked to a substantial 91 % reduction in the risk of incident cognitive impairment over 5 yrs. It has been estimated from such prospective cohort studies that reducing physical inactivity by only 25 % would prevent 1 million cases of dementia worldwide annually. Mild cognitive impairment (MCI), defined as objective and subjective cognitive decline with preserved functional independence, offers a unique window of opportunity in high-risk individuals to target neuroplasticity when the brain is still potentially able to adapt to beneficial stimulation. Building on the observational literature above, some exercise trials have led to improved cognitive performance, but the effect sizes in cognitively healthy adults have been statistically negligible, heterogeneous, and of questionable clinical relevance. However, exercise trials in those with established MCI or dementia have reported larger positive effects, particularly when the prescriptions are sufficiently robust. Unfortunately, the mechanisms of exercise benefit, or the reasons for broad individual variation in cognitive adaptations are very poorly defined. Such mechanistic insight, and longterm, robust research is critical if we are to confirm and optimise a brain-training exercise prescription so as to enhance neuroplasticity and improve cognition in high-risk or already impaired individuals.