Rats feel regret, experiment finds

With only an hour to eat, a diner hurries into his favorite restaurant. Deterred by a modest wait, he leaves, only to be burned by an even longer wait at the next restaurant. He immediately regrets his decision. This may seem like a typical “woulda, coulda, shoulda” situation — except in this case, the diner is a rat.

In laboratory tests, rodents exhibit regret, scientists report June 8 in Nature Neuroscience. After forgoing a good meal for a bad one, rats pause, glance back at what could have been and change their subsequent behavior. Scientists even caught signs of regret in rats’ brains: Nerve cells behaved as though the rats were back at the scene of the missed opportunity.

This study and other recent research are turning up hints of seemingly sophisticated behaviors in rodents which were previously thought to be exclusive to people, says neuroscientist Inbal Ben-Ami Bartal of the University of Chicago. Simple analogs of behaviors such as regret and empathy may allow scientists to better understand complex emotions in people. “We can really learn a lot about human brains from rats.”

The first hint of rat regret came unexpectedly, says neuroscientist A. David Redish of the University of Minnesota in Minneapolis. While watching rats forage for food, graduate student Adam Steiner noticed that one rat looked as though it lamented a previous bad decision.

That chance sighting led the researchers to build a regret-seeking experiment they called restaurant row. It consisted of a large arena where rats could sample four stations that served up plain food pellets or those flavored with cherry, banana or chocolate. At the entryway to each restaurant, the pitch of a chime indicated how long the rats would have to wait for sustenance.

Each rat had its own flavor preferences, Redish says, allowing the scientists to figure out which restaurants and wait times represented a sweet deal to each animal. For instance, a rat that relished chocolate would happily wait about 22 seconds for a chocolate meal but would tolerate only about a 16 second wait for a plain one. Crucially, the rats had only an hour to dine, so the pressure was on to find the most satisfying food with the shortest wait.

As four animals ran through multiple scenarios, Steiner and Redish noticed that rats that skipped a good deal and wound up with a bad one exhibited behaviors that looked like regret. The rodents paused and looked back toward a restaurant where they had turned down a good meal. After forgoing a favored meal with a short wait, rats were more likely to wait longer for a less-desirable meal at the next restaurant. And when food arrived, the rats didn’t seem to relish it as much. “Normally they’ll take 20 seconds or so to eat the food and get ready to go to the next place,” Redish says. “After the regret, they eat in three to five seconds. They just wolf the food down.”

Activity in the rats’ brains also suggested the rats were ruing missed opportunities. The researchers monitored cells in two brain regions, the orbitofrontal cortex and the striatum, that fired in a distinct pattern when each rat was in a particular restaurant. When a rat skipped a good meal of banana with a short wait time but then encountered a long wait for a less-than-ideal cherry meal, for instance, the neurons behaved as though the rat were back in the banana restaurant, the team discovered. The results suggest to Steiner and Redish that the rat was replaying its bad choice in a moment of regret.

The brain activity wasn’t caused by simple disappointment, the team found. When the rat got a bum deal but made the right decision at the previous restaurant, the animal didn’t show the same behavioral or brain signs.

“These authors have done really well to take what we think of as a complex concept such as regret and extract all complexity out of it and make it something very simple,” says Bartal, whose work has revealed signs of empathy among rats. Of course, she says, regret is a simpler sentiment in rats than it is in humans, who can mentally replay events that took place years ago.

Finding that rats express regret should allow scientists to better understand how the brain learns from its past mistakes, Redish says.