Researchers in the US have shown that age-related changes in gut bacteria composition can directly influence memory in mice. 

There is growing evidence suggesting that the gut microbiome—the community of bacteria residing in the intestines—influences the brain in various ways, including behaviour and stress. 

Researchers from Stanford Medicine asked whether age-related changes in gut bacteria would actively drive memory loss and, if so, how signals from the gut reach the brain.  The team found that as mice age, their gut microbiome shifts, with bacteria named Parabacteroides goldsteinii becoming more abundant.  

When germ-free young mice were exposed to an “old” microbiome with these bacteria — either by being housed with older mice or by receiving gut microbes from them — their memory worsened, and they performed more poorly in tests of object recognition and maze escape.  

This accumulation of P. goldsteinii was found to cause specific gut inflammation, reducing activity in both the vagus nerve, which sends signals from the gut to the brain, and the hippocampus, the brain region involved in memory formation.  

Christoph Thaiss, from Stanford and lead author of the study published in Nature, said: “We tend to think of memory decline as a brain-intrinsic process. But this study indicates that we can enhance memory formation and brain activity by changing the composition of the gastrointestinal tract — a kind of remote control for the brain.”   

P. goldsteinii also resides in the human gut microbiome, and the researchers are now investigating whether a similar pathway is present in people. Vagus nerve stimulation is already approved for depression, epilepsy and stroke recovery, so this research may inform more immediate applications for age-related memory loss.