A number of studies have demonstrated that physical exercise can reverse cognitive decline in normal aging in both humans and rodents. It has been reported that cerebral blood volume in the dentate gyrus is increased following exercise in middle-aged humans, and that the dramatic drop in adult neurogenesis accompanying aging can be improved following physical exercise in mice. The dentate gyrus is especially important for behaviors requiring pattern separation which enables animals to differentiate between highly similar contextual experiences. Aged mice showed a profound impairment in contextual discrimination compared to young animals.
Voluntary exercise rescued this deficit to such an extent that behavioral pattern separation of aged-running mice became similar to young animals. Running also resulted in a significant increase in the number of immature neurons with tertiary dendrites in aged mice. Despite this, neurogenesis levels in aged-running mice were still considerably lower than in young animals.
The authors concluded that mechanisms other than dentate gyrus neurogenesis likely play significant roles in improving behavioral pattern separation elicited by exercise in aged animals. Running does not globally improve learning and the authors concluded that its positive effects may be most beneficial for demanding cognitive behaviors like pattern separation. Adult neurogenesis alone may not fully account for the ameliorative effects of enriched environments and exercise on hippocampus-dependent behaviors.
Wu MV, Luna VM, Hen R: Running rescues a fear-based contextual discrimination deficit in aged mice. Frontiers Syst. Neurosci. 9:114, August 11, 2015 ; doi: 10.3389/fnsys.2015.00114.

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