Could've, should've, would've. Everyone has made the wrong choice at some point in life and suffered regret because of it. Now a new study shows we're not alone in our reaction to incorrect decisions. Rats too can feel regret.

Regret is thinking about what you should have done, says David Redish, a neuroscientist at the University of Minnesota in Minneapolis. It differs from disappointment, which you feel when you don't get what you expected. And it affects how you make decisions in the future. (See "Hand Washing Wipes Away Regrets?")

If you really want to study emotions or feelings like regret, says Redish, you can't just ask people how they feel. So when psychologists and economists study regret, they look for behavioral and neural manifestations of it. Using rats is one way to get down into the feeling's neural mechanics.

Redish and colleague Adam Steiner, also at the University of Minneapolis, found that rats expressed regret through both their behavior and their neural activity. Those signals, researchers report today in the journal Nature Neuroscience, were specific to situations the researchers set up to induce regret, which led to specific neural patterns in the brain and in behavior.

Making Choices

When Redish and Steiner looked for neural activity, they focused on two areas known in people—and in some animals—to be involved in decision-making and the evaluation of expected outcomes: the orbitofrontal cortex and the ventral striatum. Brain scans have revealed that people with a damaged orbitofrontal cortex, for instance, don't express regret.

To record nerve-cell activity, the researchers implanted electrodes in the brains of four rats—a typical sample size in this kind of experiment—then trained them to run a "choice" maze.

The maze consisted of a circle with four spokes radiating out from its circumference. At the end of three spokes was food flavored with banana, cherry, or chocolate. At the end of the fourth spoke was unflavored food. When a rat arrived at a spoke, a tone would sound before it received the food. The tone's pitch indicated how long the rat would have to wait before getting the treat; it could be anywhere from one to 45 seconds.

The rat then had to make a choice. It could either wait the allotted time before getting the food, or it could move on to the next spoke. The rats were allowed to run the maze for only an hour, so their "foraging" needed to be as efficient as possible.

Bad Choices

Each rat had its own preferences regarding flavor and patience. And those preferences manifested in specific nerve-cell patterns in its brain. Redish and Steiner could thus tell when a particular rat was thinking about, say, the chocolate-flavored versus the cherry-flavored food.

When a rat passed up food at one spoke and moved on to the next, then realized it would have to wait even longer for food at the second spoke, two things happened: It would look back to the previous spoke, and the specific nerve-cell pattern in its brain that represented that first choice would light up.

"That's the regret," says Redish. Not only were the rats physically looking backward; they were also thinking about the choice they hadn't made.

What's more, "just like humans," says Redish, the rats were more likely to take a "bad deal"—or wait longer than they normally would for their next piece of food—after a regretful decision. The rats would also hastily consume food that stemmed from a bad choice, spending only about five seconds with the treat. Normally the rats would spend about 20 seconds grooming themselves and eating their food.

Looking Forward

Rats that met with disappointment reacted very differently. Some would sit and look at the choice in front of them. Others would visualize their next choice. These rats, says Redish, were looking toward the future.

Matt Roesch, a neuroscientist at the University of Maryland in College Park who was not involved in the study, was intrigued by the experiment. Finding a human emotion like regret in an animal, he says, and being able to see it manifested in brain activity is exciting.

"If you have a strong feeling of regret, you should be able to use that information to guide future decisions, to make better ones," Roesch says. Yet people who have psychiatric diseases like schizophrenia can't do this. Alcoholics and drug addicts also seem unable to make better decisions based on their regret. (See "NIDA's Director Tells Us What We Know—and Need to Know—About Marijuana.")

Roesch, who studies the neural basis of addiction, says he would love to see a future study on whether addiction in rats changed the results of the experiment.

Redish would also like to be able to translate what he's seen in his rats to human behavior. "Humans avoid regret," says Redish. "Do rats?"