When aging attacks the latest developments in our brain

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Since separating from our cousin the chimpanzee more than six million years ago, the human brain has been enriched with brain tissue essential for taking decision-making and self-control. Paradoxically, These same regions are the first to suffer the onslaught of aging. The latter, the most evolved of all, are also the most vulnerable to the passage of time. This discovery, published in Science Advances on August 28, offers us a new perspective on brain evolution and the aging process.

The price to pay for our cognitive superiority

The study, conducted by an international team of researchers, compared MRI images of human and chimpanzee brains (Pan troglodytes). The results are indisputable: the areas of the human brain that have expanded most rapidly during evolution are also those that deteriorate most rapidly with age.

«“The most recent and evolutionarily important changes are where aging has the greatest effect,” says Felix Hoffstaedter, a neuroscientist at the Jülich Research Center in Germany and co-author of the study. This observation tends to confirm the hypothesis that our cortical expansion (increase in the surface area and complexity of the cerebral cortex) has come at the cost of age-related decline, as Rogier Mars, a neuroscientist at the University of Oxford, points out.

A revealing comparative map

The researchers analyzed MRI scans of 189 chimpanzees aged 9 to 50 and 480 humans aged 20 to 74. They found that while the two species shared many anatomical similarities, particularly in the prefrontal cortex, the differences in the aging process were striking.

In humans, the greatest loss of gray matter is in the frontal cortex, including the prefrontal cortex. This region, involved in complex cognitive functions such as language, working memory, and decision-making, is also linked to Alzheimer's disease and several types of dementia. In chimpanzees, on the other hand, it is the striatum, a central structure involved in the formation of habits and reward-related behaviors, which suffers the most damage.

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A human specificity ?

To confirm that this phenomenon is specific to humans, the researchers extended their study to other primates: the olive baboon (Papio anubis) and the rhesus macaque (Macaca mulatta). In these two species, no link was observed between the areas of the brain that had undergone rapid evolutionary expansion and those undergoing accelerated aging.

This human particularity raises questions; Could our remarkable cognitive capacity be intrinsically linked to an increased vulnerability to aging?? Has evolution favored short-term advantages over longevity ?

While these results open up new perspectives in understanding neurodegenerative diseases, they also call for further research into this type of research. Rogier Mars suggests studying other aspects of brain aging, such as changes in connections between brain regions and gene expression profiles.

Studying brain aging through the prism of evolution therefore offers us a new axis of analysis concerning our own nature. It reminds us that our extraordinary cognitive ability, the product of millions of years of evolution, is not without cost. Understanding this evolutionary trade-off could be the key to better understanding and, perhaps one day, in the best-case scenario, helping us to slow age-related cognitive decline.

• The brain regions that have evolved the most in humans are also the most vulnerable to aging.
• The prefrontal cortex, involved in complex cognitive functions, deteriorates more quickly in humans than in other primates.
• This vulnerability to aging seems to be the price to pay for our cognitive evolution, which is faster than that of other primates.

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