Life expectancy has increased steadily over the past century. However, in many cases, that prolonged life expectancy comes at the expense of quality of life. Most people wish to leave life with dignity, sustaining independent living and making their own decisions. This may explain why most adults are, for the first time, more worried about the loss of cognitive abilities than cancer or heart disease (1).
Many adults fear developing Alzheimer’s disease as they get older. While that specific fear may not come to pass, cognitive decline does frequently occur as brains age. Among the cognitive faculties that diminish as we get older are executive functioning and memory. Executive functions include maintaining information in working memory, updating information to accommodate new data, and inhibiting inappropriate responses.
Compromised memory and executive skills often translate into a loss of function in daily life. Age-related cognitive decline has been related to selective brain changes in the prefrontal and temporal/hippocampal brain areas—crucial for executive function and memory, respectively.
Thus, interventions to slow down brain aging have been proposed. Two types of non-pharmacological solutions have been intensely explored: cognitive training and physical exercises. But which one is better? And how do scientists measure the effectiveness of these interventions to ensure that they work?
What We Know About Brain Aging Exercises
Some physiological parameters decline with age, such as cerebral blood flow (CBF), cerebral vascular reactivity (CRV), and white matter (WM) and grey matter volume (GMV)—particularly in the prefrontal lobes (2). These variables can be captured by MRI scanners to measure the effectiveness of proposed interventions.
CBF is responsible for energy homeostasis in the brain. CBF is the brain's fuel and it is typically constant. CRV is the ability of the blood vessels to vaso-dilate. It is a marker of vascular brain health. One way to induce CRV response is by exposing the brain to CO2 (3). CBF has been known to decline by 0.35 percent per year over the lifespan, whereas GMV declines approximately 0.85 percent annually (4). There are gender differences in the effects of aging on blood flow.
Both physical exercise and cognitive training have been associated with improvements in these physiological parameters. For example, one recent study explored the effects of aerobic exercises on white matter integrity (5). The participants ranged in age between 60 and 79 years. Aerobic walking positively correlated with improved white matter physiology and memory functioning. In other words, short-term aerobic intervention slowed down the aging of white matter in older adults. Studies exploring cognitive training, on the other hand, have employed different protocols and different physiological measures. Generally, cognitive training resulted in functional and structural brain improvements.
Is One Better Than the Other?
Fewer studies directly compare cognitive training and physical exercise. One study measured the effects of training on both CBF, CRV, and a battery of neurocognitive measures in normally aging middle to older age adults (6). The cognitive battery was administered before the 12-months training started (baseline), mid-training, and at the end of training for cognitive and physical groups.
The researchers found that cognitive training improved executive function whereas physical training enhanced memory. Specifically, they reported improvements in complex abstraction and working memory in the cognitive training group as well as enhanced immediate and delayed memory in the physical training group.
Improvements in memory were correlated with an increase in hippocampal blood flow in the group who engaged in physical exercise. The hippocampus is crucial for long-term memory and is particularly vulnerable to aging and dementia. In other words, participants who enjoyed the most memory improvements showed the highest CBF changes in the hippocampus.
There was also a linear increase in CBF in areas important to executive function, such as the prefrontal cortex. In other words, the increases in cognitive performance did not plateau within the period of the study. The cognitive training consistently increased blood flow to the prefrontal cortex.
Cognitive performance enhancements are important for daily independent living such as making financial decisions. Similarly, physical exercise can rescue the memory loss associated with aging, which is crucial for everyday functioning; memory loss is probably the number one complaint as we age.
Training increased CBF in various areas for both types of training but did not cause a concomitant change in CVR. This was interpreted as an increase in neuronal demand rather than vasculature change in the groups. Thus, cognitive training resulted in the improvement of neuronal health in several areas in the brain—the cingulate cortex and prefrontal region—whereas physical training improved neuronal health in the hippocampus. These improvements in how neurons in these areas demand energy were not necessarily related to improvements in brain vasculature. Neurons became more efficient in using energy after the training.
Another recent review combined the results from 38 studies to compare the effects of cognitive and physical training on brain MRI in healthy older adults (7). They found that cognitive training was associated with improvements in white matter microstructure, while physical training was associated with macrostructural improvements, and both demonstrated changes to task-based MRI signals.
Most of the studies showed beneficial effects for cognitive and physical training on one or more brain measures. Specifically, cognitive training is associated with subtle micro-changes in axons such as myelination (the covering of neurons that speeds up information processing), synaptogenesis (making new connections), and angiogenesis (formation of new blood vessels which nourishes brain cells). Physical exercise leads to increases in grey and white matter volumes. It is still unclear what these training-related physiological changes in the brain mean in terms of improvements in cognition.
What Should You Do to Protect Your Brain?
Based on many studies, here is the best "prescription" I can offer: physical aerobic exercises, such as walking, three times a week for at least six months, plus cognitive training that is general to address multi-faculties of executive functioning, for at least 10 weeks (as opposed to focused memory training). It's also important to start the training as young as possible, in order to enter the aging process with the healthiest brain possible.
(1) http://iom.nationalacademies.org/Reports/2015/Cognitive- Aging.aspx
(2) Lu, H., Xu, F., Rodrigue, K. M., Kennedy, K. M., Cheng, Y., Flicker, B., et al. (2011). Alterations in cerebral metabolic rate and blood supply across the adult lifespan. Cereb. Cortex 21, 1426–1434. doi: 10.1093/cercor/bhq224.
(3) Yezhuvath, U. S., Lewis-Amezcua, K., Varghese, R., Xiao, G., and Lu, H. (2009). On the assessment of cerebrovascular reactivity using hypercapnia BOLD MRI. NMR Biomed. 22, 779–786. doi: 10.1002/nbm.1392.
(4) Chen, J., Rosas, H., Salat, D., 2011. Age-associated reductions in cerebral blood flow are independent from regional atrophy. Neuroimage 55, 468–478. https://doi.org/ 10.1016/j.neuroimage.2010.12.032.
(5) Colmenares, A. M., Voss, M. W., Fanning, J., et al. (2021). White matter plasticity in healthy older adults: the effects of aerobic exercise. NeuroImage, 239, 118305.
(6) Chapman, S.B., Aslan, S., Spence, J.S., Keebler, M.W., Laura, F.D., Didehbani, N., Perez, A.M., Lu, H., Mark, D., 2016. Distinct brain and behavioral benefits from cognitive vs. physical training: a randomized trial in aging adults. Front. Hum. Neurosci. 10, 338. https://doi.org/10.3389/fnhum.2016.00338.
(7) Intzandt, Vrinceanu, Huck et al. (2021). Comparing the effect of cognitive vs. exercise training on brain MRI outcomes in healthy older adults: A systematic review. Neuroscience and Biobehavioral Reviews: 511-533.