Is your memory getting worse as you get older? Your gut microbiota could be to blame.

It's still not entirely clear why, as we accumulate gray hair, we lose cognitive abilities and our memory begins to fail us. Neuroscience points to decreased blood flow to the brain; to the natural loss of gray matter volume with age; or to the fact that neuronal repair mechanisms, like everything else, are no longer as efficient and begin to fail. To all these potential reasons, scientists now add another: the gut microbiotaIn a study conducted with mice, a team from Stanford University has found that a bacterium that proliferates in the rodents' gut with age plays a key role in the animals' cognitive decline. They have observed that this bacterium, called P. Goldsteinii, It produces molecules that prevent the neurons connecting the gut and brain from communicating. This, in turn, reduces activity in the hippocampus, a seahorse-shaped region of the brain responsible for learning and forming new memories.

"Although memory loss is common with age, it affects people very differently," notes Christoph Thaiss, co-author of this research, in a press release. published in Nature. “We wanted to understand,” she continues, “why some elderly people have clear minds, while others begin to experience cognitive decline in their 50s or 60s.” And what they found is that, contrary to what was assumed in this area of ​​research, it seems that the decline in cognitive abilities is not linked to the brain's wiring, but rather that the body actively modulates it. “The gastrointestinal tract plays a critical role in this process,” Thaiss emphasizes. The gut-brain axis

For the past couple of decades, there has been a great deal of research on the gut-brain axis. It is, in fact, a rapidly growing area of ​​study, from which discoveries have emerged showing the close link between these two organs. For example, it has been observed how people with mental disorders or neurodegenerative disease, such as Alzheimer's People with Parkinson's disease have a dysfunctional gut microbiota, although it's unknown whether this is a cause or a consequence of the disease. Experiments in mice have shown how gut bacteria are linked to anxiety and depression. And there are indications that they could play a significant role in humans; so much so that, in fact, the symptoms of mild depression are already being treated with certain probiotics.

This Stanford study follows this line of inquiry. Researchers took gut microbiota from older mice with reduced cognitive ability and gave it to younger mice. They found that the younger rodents with bacteria from older mice performed worse on the tests presented to them than their counterparts who hadn't received any. When the researchers treated the mice with antibiotics, which destroy the gut microbiota, the animals performed well again.

Of all the most abundant bacteria in the intestines of old rodents, they focused on P. GoldsteiniiThey conducted further experiments and found that this microorganism produces medium-chain fatty acids. When young mice were fed these molecules, they observed that they triggered an inflammatory immune response that decreased activity in the vagus nerve, a kind of highway connecting the brain and gut, and also in the hippocampus. When vagus nerve activity was stimulated in the animals, older mice regained cognitive ability and were able to remember new objects and escape mazes more quickly, just like the younger mice. If these results are replicated in humans, this could pave the way for finding drugs and interventions to modulate the gut microbiota that would help combat age-related cognitive decline.