A new study shows that, like humans, rats can also feel regret. The results of the study mark the first time that such an emotion has been observed to occur in a nonhuman organism.

A U.S.-based team of researchers from the University of Minnesota conducted the study in an effort to gain a deeper understanding regarding learning and behavior in humans and animals. The neuroscientists wanted to see whether an emotion such as regret could be conclusively observed in rats.

"Disappointment entails the recognition that one did not get the value expected," said the study's authors. "In contrast, regret entails recognition that an alternative (counterfactual) action would have produced a more valued outcome." The researchers published their findings in the online journal Nature Neuroscience.

To conduct the study, the researchers tried to expose the rats to scenarios wherein the test subjects had to pick between waiting for specific periods of time to obtain a piece of food as a reward or choosing to go after another food source. Based on their observations, the scientists saw that the decision the rats made seemed to have an effect on future decisions.

The test the rats, the scientists constructed an experiment where the rats were forced to make a decision in a scenario referred to as "Restaurant Row." The test subject had to choose between different food items, with each specific item involving a predetermined waiting period. All in all, the scenario lasted a total of one hour. The researchers likened the scenario to waiting in line at a restaurant. Different restaurants may have varying lines and if a certain line is too long, people often move on to other dining options.

Some of the rats chose to move on to other options while the others were willing to wait. The rats that chose to move on actually made a "bad decision," and may have induced regret. The rats were soon looking toward the food that they chose to abandon before moving on to the next source. However, in subsequent tests, these same rats were seen to be more patient, staying in place and waiting for the reward to come. This observation was construed as a sign of regret.

These observations imply that emotions akin to regret may also be observed in other animals. However, the researchers tried to make a distinction between the emotions regret and disappointment. The neuroscientists clarified regret as the knowledge that a decision was incorrect and choosing other options may lead to better outcomes. On the other hand, disappointment defined a situation wherein the best outcome was not realized. To make the distinction between the two, the actual decision the rats made was a key indicator.

"In these situations, rats looked backwards toward the lost option, cells within orbitofrontal cortex and ventral striatum represented the missed action, rats were more likely to wait for the long delay, and rats rushed through eating the food after that delay," said the study.