New study expands understanding of the ‘gut-brain axis’.

Scientists have discovered that resident bacteria of the intestine, collectively known as the gut microbiome, can influence the ability to overcome fear.

The finding, published in the journal Nature, could one day help people with post-traumatic stress disorder. It also dramatically expands understanding of the “gut-brain” axis, which is known to have a hand in depression, anxiety and autism.

The researchers, led by immunologist David Artis at Cornell University in New York, US, started by putting the frighteners on a bunch of mice – some healthy and others treated with antibiotics to wipe out their gut bacteria.

They followed standard procedure for getting mice scared. They put the critters in a special chamber where a tone sounded for 30 seconds. When the tone stopped the mice got an electric shock to their feet through the floor.

As you might expect, it wasn’t long before they started freezing with fear as soon as they heard the tone – your paradigm case of Pavlovian conditioning.

Fortunately for mice, however, fear can be unlearned.

In the best of all possible worlds, when the tone is sounded later without the shock, mice will eventually stop freezing when they hear it. Which is exactly what happened to the normal mice. But the antibiotic-treated mice just couldn’t stop freezing to the tone, long after the shocks had stopped.

Now that sounds a lot like returned soldiers who can’t dial down the fear when a helicopter flies overhead or they walk down an eerily empty street, just a couple of potential triggers for post-traumatic stress.

Which is all the more reason to find out why those mice without microbes were so bad at unlearning fear.

The researchers started working through their suspect list.

Read the full story in Cosmos magazine here