It’s last week, my fridge is empty. I hop onto a train with two restaurants in mind: restaurant 1 is just one station away, while restaurant 2 has a hazelnut mousse that sends me to heaven every time. But I’m in a rush, so when the train doors open at the first stop, I step out. Yet when I get to restaurant 1, the queue for tables is out the door.
Regret. According to a new study by University of Minnesota researchers, rats feel it too.
David Redish and his graduate student Adam Steiner developed a task, which they dubbed “Restaurant Row”, in which rats have just 60 minutes to run around a circle with four spokes, each one leading to a different flavour of food. As the rat passes each spoke, a tone sounds to indicate how long it has to wait for that flavour of food, an offer the rat can either take or leave. “This rat can say I’m not waiting 30 seconds for a cherry-flavoured food pellet, I’m going to skip it and try my luck at the banana restaurant next in line”, says Redish.
For each flavour, rats have a threshold for how long they are willing to wait based on their individual preferences. Steiner and Redish used these waiting-time thresholds to determine what was a good food option and what was a bad food option for the rat. Occasionally, the rat would skip a good deal and then encounter a bad deal. “What happens then is the rats pull up short, they look backwards; and I mean anthropomorphically they look like they’re frustrated”, Redish explains.
The researchers compared the behaviour of the rats in these regret-inducing conditions with “disappointment” conditions in which rats were offered a bad food option after making the right choice at the previous restaurant. In regret conditions, rats not only looked backwards, but were also more likely to take the bad deal they were now faced with and to consume the food more quickly.“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”
“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”.
Next, Steiner and Redish recorded neural activity in a brain region called the orbitofrontal cortex (OFC), which if damaged can make humans incapable of expressing regret. They found that in regret situations the activity of a cell in the OFC strongly resembled its activity when the rat entered the previous restaurant, even though the rat was presently in a different location. Perhaps more surprisingly, when they looked at the population of cells as a whole, they found that in regret-inducing moments, the activity of cells represented the entry point into the restaurant they had passed on more strongly than the meal they had missed out on. The authors contend that rats here are actually regretting the action they didn’t take, since the entry point into the restaurant is where the decision not to wait was made.
This study builds on previous work the year before that showed rodents were able to do mental time travel into the future, with sequences of activity in the hippocampus (involved, among other things, in spatial navigation) of the rat brain predicting the journey the animal was about to take. If rats can experience regret, they can imagine not just future paths, but also paths in the past that they might have taken. The authors are however careful to point out that regret in rats may not be quite the same as in humans. For example, it seems doubtful that rats can regret a decision that they made last week. I, however, am still regretting my missed hazelnut mousse.
For the original study see: Steiner AP & Redish AD (2014) Behavioral and neurophysiological correlates of regret in rat decision-making on a neuroeconomic task. Nature Neurosci 17(7):995–1002.
Hedi Young is a PhD student at the Cortical Circuits lab, Champalimaud Neuroscience Programme.
Edited by: Ana Nunes (page editor), Clara Ferreira (editor-in-chief)