Researchers found that changes in the gut microbiome with age trigger immune responses that hamper the vagus nerve, a key communicator between the gut and brain. This, in turn, reduces hippocampal activity, impairing memory and learning.
Senior author Christoph Thaiss, assistant professor of pathology at Stanford University, said, “We learned that the timeline of memory decline is not hardwired; it is actively modulated in the body, with the gastrointestinal tract playing a critical role.”
The study, published in Nature, examined young (two-month-old) and old (18-month-old) mice housed together, allowing microbial exchange.
Ageing mice also showed increased abundance of Parabacteroides goldsteinii, associated with cognitive decline.
Colonising young mice with this bacterium impaired their memory and maze navigation, confirming the microbiome’s role in cognitive function.
Stimulating the vagus nerve in older mice restored memory and learning performance to levels comparable with those of younger animals.
“Since the gastrointestinal tract is easily accessible, modulating the gut microbiome and its metabolites offers a promising strategy to control brain function,” senior author Maayan Levy noted.
The researchers further identified medium-chain fatty acids produced by P goldsteinii that activate gut myeloid cells, triggering inflammation.
This inflammation disrupts vagus nerve signalling and inhibits hippocampal activity, undermining memory formation.
The findings, however, highlight the potential of gut-targeted interventions to slow or reverse age-related cognitive decline.
Modulating gut microbiome composition, alongside targeted vagus nerve stimulation, may offer a non-invasive approach to preserve memory and maintain brain health as populations age.
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