A study published in the very prestigious journal Nature indicates that memory loss associated with aging is due to blood inflammatory factors that prevent the formation of new nerve cells. Adopting lifestyle habits that reduce inflammation, including physical exercise, could therefore greatly contribute to the maintenance of brain function.
Although it was long thought that the quantity of nerve cells in the brain (neurons) no longer varied in adulthood, we now know that brain tissue contains stem cells capable of forming new functional neurons. These new neurons, resulting from the process of neurogenesis, are important because they allow the brain to rely at all times on “efficient” cells to carry out the processes essential to memory and to the acquisition of new knowledge. Several studies have also shown that the memory loss that frequently affects the elderly was associated with a reduction in this neurogenesis. This decrease in new neurons does not seem inevitable, however, since other studies have clearly shown that certain activities, in particular physical exercise, preserve neuronal regeneration as well as cognitive functions. It is therefore probable that certain factors present in the organism influence the process of neurogenesis.
Blood, carrier of youth or old age
To identify these factors, a team of Californian researchers transfused blood from an old mouse to a young mouse and, in parallel, transfused blood from a young mouse to an old mouse. This “blood link” has astonishing repercussions when an old mouse is brought into contact with the circulation of a young mouse: neurogenesis is considerably increased in the old mouse while it is reduced in the youngest! Moreover, when a young mouse is repeatedly injected with the blood of an old mouse, its learning abilities are diminished. These observations suggest that with age the blood accumulates factors that reduce the formation of new neurons and cause a decrease in cognitive abilities.
Memory loss associated with chronic inflammation
By comparing the blood of young and old mice, the researchers noticed that the decline in cognitive functions that accompanies aging was correlated with a significant increase in the levels of CCL11, a protein known to play a role in inflammatory processes. The importance of this factor
seems huge: when CCL11 levels are increased in young mice, they show reduced neurogenesis as well as cognitive problems that are normally only seen in older animals! Since the amounts of this inflammatory protein also increase with age in humans, these observations therefore suggest that the reduction in neurogenesis and memory loss associated with aging are direct consequences of inflammation.
Physical activity, the best ally against chronic inflammation
This discovery is capital, because it makes it possible to think that it is possible to influence concretely the aging of the brain by controlling the levels of inflammatory molecules present in the blood circulation. In this sense, it is interesting to note that activities that exert a powerful anti-inflammatory action, in particular physical exercise, are recognized as one of the main lifestyle factors capable of reducing the decline of cognitive functions and the risk of neurodegenerative diseases. So don’t let winter intimidate you: whether it’s downhill or cross-country skiing, snowshoeing, skating or sledding, there are plenty of opportunities to get active to maintain your muscle tone… and your memory!
Villeda SA et al. The aging systemic milieu negatively regulates neurogenesis and cognitive function. Nature ; 477:90-94.
Ahlskog JE Physical exercise as a preventive or disease-modifying treatment of dementia and brain aging. Mayo Clin Proc; 86:876-84