A 2008 review of cognitive enrichment therapies (strategies to slow or reverse cognitive decline) concluded that "physical activity, and aerobic exercise in particular, enhances older adults' cognitive function". http://www.psychologicalscience.org/journals.pdf
In mice, exercise improves cognitive functioning via improvement of hippocampus-dependent spatial learning, and enhancement of synaptic plasticity and neurogenesis. In addition, physical activity has been shown to be neuroprotective in many neurodegenerative and neuromuscular diseases. For instance, it reduces the risk of developing dementia. Furthermore, anecdotal evidence suggests that frequent exercise may reverse alcohol-induced brain damage.
There are several possibilities for why exercise is beneficial for the brain. Examples are as follows:
increasing the blood and oxygen flow to the brain
increasing growth factors that help create new nerve cells and promote synaptic plasticity
increasing chemicals in the brain that help cognition, such as dopamine, glutamate, norepinephrine, and serotonin
Physical activity is thought to have other beneficial effects related to cognition as it increases levels of nerve growth factors, which support the survival and growth of a number of neuronal cells.
Exercise has been found to positively regulate hippocampal neurogenesis, which is considered an explanation for the positive influence of physical activities on memory performance. Hippocampus-dependent learning, for example, can promote the survival of newborn neurons which may serve as a foundation for the formation of new memories. Exercise has been found to increase the level of brain-derived neurotrophic factor (BDNF) protein in rats, with elevated BDNF levels corresponding with strengthened performance on memory tasks. Data also suggests that BDNF availability at the beginning of cognitive testing is related to the overall acquisition of a new cognitive task and may be important in determining the strength of recall in memory tasks.
See also: http://en.wikipedia.org/wiki/Physical_exercise
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