Edward Chen in Nature:
A species of gut bacteria that proliferates as mice get older plays a part in cognitive decline, a study finds1. 
Researchers determined that the bacterium interferes with signalling along sensory nerves that connect to the brain.
Although the experiments were conducted in mice, the gut–brain circuit that the team identified “is likely conserved in humans”, says David Vauzour, a biochemist at the University of East Anglia in Norwich, UK. That would need to be confirmed, but if the circuit is present in humans, then this research could reveal a mechanism that explains why people’s memory and ability to learn naturally decreases with age — and offer hope that gut-targeted therapies could reverse the decline.
The effects of the bacteria, which dampens the gut–brain circuit in mice, seem similar to other consequences of ageing. “When we get older, we need things like glasses and hearing aids”, says co-author Christoph Thaiss, an immunologist at Stanford University in California. The study — published today in Nature1 — shows that, just as ageing causes a decline in sensory perception of the external world, it might also be causing a loss of perception of internal signals, too, he says.
More here.
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