Stanford study links gut bacteria to age-related memory loss

Old mice got smarter when researchers tweaked their gut bacteria and stimulated the vagus nerve — restoring cognitive performance to young-animal levels, according to Stanford Medicine.

The study, published in Nature, traced the mechanism in detail. A bacterium called Parabacteroides goldsteinii proliferates as mice age and triggers the release of medium-chain fatty acids that set off an inflammatory immune response in gut myeloid cells. That inflammation impairs signaling through the vagus nerve to the hippocampus, where memories form.

To prove that the gut was driving the decline, the team cohoused young mice (2 months old) with old ones (18 months old) for a month. The young mice picked up the aged microbiomes and promptly performed worse on memory and spatial navigation tests. Germ-free young mice given old-mouse microbiomes showed the same decline.

"The degree of reversibility of age-related cognitive decline in the animals just by altering gut-brain communication was a surprise," said Christoph Thaiss, an assistant professor of pathology at Stanford and senior author.

Vagus nerve stimulation is already FDA-approved for depression, epilepsy, and stroke recovery. If the gut-brain pathway works similarly in humans, existing devices could be repurposed to address age-related memory loss. The team also found that treating old mice with molecules that activate the vagus nerve restored their cognitive performance to match that of young animals.

"We can enhance memory formation and brain activity by changing the composition of the gastrointestinal tract — a kind of remote control for the brain," Thaiss said.

Previously:

• The psychobiome is bacteria that affect behavior and mental health