David Redish and his graduate student Adam Steiner of the University of Minnesota didn't set out to study if rats experience regret.

They were looking at decision-making in rats. But something about the behavior of their subjects struck them as interesting. When a rat made a mistake, it stopped and looked backwards. Anthropomorphically, it looked to Steiner and Redish as if the rat was feeling regret.

That observation lead the researchers to design an experiment to induce regret in rats and then measure behavioral and neurophysiological markers consistent with regret. The results were published June 8 in Nature Neuroscience.

Let's Make A Deal

Regret can be defined as the ability to represent the counter-factual: what might have been. It's different from disappointment, which is simply when things aren't working out. "Regret is the recognition that you made a mistake and if you had done something differently, things would have gone better," says Redish. (Redish says this is his favorite meme about regret).

The Restaurant Row task. Photo courtesy David Redish.

Steiner and Redish trained rats to do a task they call "restaurant row." The rat ran around a circle past a series of four spokes, each leading to a different flavor of food. As the rat came to the entrance of each spoke, a tone sounded that indicated how long it would have to wait to receive that specific flavor of food. The rat could choose whether to stay or go, depending on how much it liked that food and how long it would have to wait.

Redish compares it to the experience of opening the door to a restaurant and seeing how long it will take to be seated. "You can wait at the Chinese restaurant and eat there, or you can say, 'Forget it. This wait is too long,' and go to the Indian restaurant across the street," he says.

Just like you don't know if the wait at the Indian restaurant will be any shorter than the wait at the Chinese restaurant you just left, the rats in this task didn't know how long the wait at the next flavor would be.

It turns out the rats each had a threshold based on their individually distinct preferences for the different flavors. Steiner and Redish used these individual thresholds to identify what was a good deal and a bad deal for each rat. For example, one rat might be willing to wait 20-seconds for a cherry-flavored pellet (a good deal), but that same wait for a chocolate-flavored pellet might be too long (a bad deal).

Steiner and Redish wanted to know what would happen when a rat skipped a good deal and then found out the next restaurant was a bad deal. (In one example, a rat that had an 18-second threshold for both cherry and banana skipped the cherry option when the wait was only 8 seconds. Then it came to the banana option and the wait was 25 seconds.)

In these situations, the rat stopped and looked back at the previous restaurant it had passed on. "It looked like Homer Simpson going, 'D'oh!'" says Redish.

Steiner and Redish compared the behavior of the rats in regret conditions (skipping a good deal only to find themselves with a worse deal) to what they did in disappointment conditions (they made the right choice — taking a good deal or skipping a bad deal — but the next restaurant was a bad deal anyway).

The rats showed three behaviors consistent with regret. First, the rats only looked backwards in the regret conditions, and not in the disappointment conditions. Second, they were more likely to take a bad deal if they had just passed up a good deal. And third, instead of taking their time eating and then grooming themselves afterwards, the rats in the regret conditions wolfed down the food and immediately took off to the next restaurant.

Representing the What-Might-Have-Been in the Brain

Steiner and Redish also recorded neural activity from the rats' orbitofrontal cortex, an area of the brain involved in the human experience of regret.

Some cells fired in response to particular flavors, and some cells fired when the rat entered a particular restaurant. Both flavors and the moment the rat entered a restaurant were represented in their brains by particular patterns of neural activity.

In the regret conditions, Steiner and Redish saw a small amount of activation of the previous flavor (the good deal the rat had passed up). But they saw a huge representation of the previous entry point into the restaurant they skipped. When the rats looked back at a restaurant where they could have received a good deal but chose not to wait, neurons in their orbitofrontal cortex were representing the moment they had made the wrong decision.

"This matches the human experience of regret," says Redish. "You don't regret the things you didn't get; you regret the thing you didn't do."

Photo courtesy David Redish.

Although their behavioral and neurophysiological results suggest similarities to human regret, Redish says he doesn't know if rats have the same introspective experience of regret as humans. "We know their brains are doing the same calculation of the what-might-have-been that humans do when we feel regret," he says. "That calculation is about the recognition of the previous option and what you should have done."

Redish believes their results speak to a continuity between humans and other animals. "We're not surprised by hearts or legs being similar, so why should we be surprised that brain structures and computations are similar?" he says.

That doesn't mean regret is the same in humans and rats; as Redish points out, deliberating over the choice of flavored food pellet is not the same as deliberating over which college to attend, and we don't see rats doing the latter.

But even though we can't say for sure what these rats are feeling, their behavior and neural activity patterns reflect the subtleties of regret seen in humans. Their neural activity represented not the reward they missed, but the action they didn't take. And they changed their behavior, taking bad deals and rushing through them as if they were just trying to get it over with.

They may not lie awake at night ruminating over their regrets, but rats certainly show they can recognize the what-might-have-been.

Reference:

Steiner, A. P. and Redish, D. (2014). Behavioral and neurophysiological correlates of regret in rat decision-making on a neuroeconomic task. Nature Neuroscience, June 8, 2014. doi: 10.1038/nn.3740.

Homepage image: Artur Malinowski/Flickr