“Regret is useless in life,” Marlon Brando once said. “It's in the past. All we have is now.” An interesting view but a perspective many people disagree with, insisting instead that regret serves the purpose of directing our future actions. If you regret having done something, you won’t do it again, many would say, and for this reason, it is a very useful emotion. In either case, many people in all likelihood assume that humans alone experience feelings of remorse, but a new study finds the opposite may be true. Scientists at the University of Minnesota Department of Neuroscience have conducted a series of experiments that suggest rats also experience regret.

"Regret is the recognition that you made a mistake, that if you had done something else, you would have been better off," said Dr. A. David Redish, a professor of neuroscience. Working with Adam Steiner, a graduate student of neuroscience and lead author of the study, Redish devised a task in which rats were asked how long they were willing to wait for certain foods. "The difficult part of this study was separating regret from disappointment, which is when things aren't as good as you would have hoped," Redish noted. "The key to distinguishing between the two was letting the rats choose what to do."

Restaurant Row

In their new experiment named "Restaurant Row," Redish and Steiner trained the rats to run 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 the rat would have to wait to receive that specific flavor of food. At this point, 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. "It's like waiting in line at a restaurant," said Redish in a press release. "If the line is too long at the Chinese food restaurant, then you give up and go to the Indian food restaurant across the street."

Past studies have proven rats are willing to wait longer for certain flavors, suggesting they have individual preferences. In this experiment, Steiner and Redish measured each rat’s preferences and so understood what each rat would consider a good or bad deal. For example, one rat might happily wait 20 seconds for a cherry-flavored pellet (a good deal), but that same wait for a less appealing chocolate-flavored pellet might be too long (a bad deal). Meanwhile, at each instance of choice, the rats — just like humans who leave a long line at one restaurant to try another — never knew how long the wait at the next flavor would be.

Redish and Steiner wanted to know what would happen when a rat skipped a good deal only to discover the next restaurant was a bad deal. (The rat who preferred cherry, for instance, skipped a cherry option requiring a wait time of 10 seconds only to arrive at a chocolate option with a wait time of 25 seconds.)

What did Redish and Steiner observe? In these situations, the rat stopped and looked back at the previous restaurant it had left. "In humans, a part of the brain called the orbitofrontal cortex is active during regret,” Redish said. For the rats, though, the case was slightly different, as the two neuroscientists not only saw activity in the orbitofrontal cortex, where decision-making commonly takes place, but also in the ventral striatum, considered to be the reward center within a rat's brain.

Not only did the rats look backward, they were also more likely to take a bad deal if they had just passed up a good deal. Worse, instead of taking their time as usual, first eating and then grooming themselves, the regretful rats would wolf down their food and rush to the next restaurant without cleaning themselves.

“Interestingly, the rat's orbitofrontal cortex represented what the rat should have done, not the missed reward. This makes sense because you don't regret the thing you didn't get, you regret the thing you didn't do," said Redish, who hopes to do additional experiments that might help him understand how humans make decisions following regret.

Source: Steiner AP, Redish AD. Behavioral and neurophysiological correlates of regret in rat decision-making on a neuroeconomic task. Nature Neuroscience. 2014.