We often find ourselves in decision-making dilemmas along the day. For instance, to reach work on time, would you rather take the shorter, faster route or the longer, scenic route? In deciding these actions, the brain promptly fits in a reward versus risk equation, but sometimes the outcome isn’t quite favorable! What if there was an accident along the shorter route, and the traffic delays you even more than the longer route would have?
This feeling of what-could-have-been, simply called regret, is a universal human experience. It occurs when your brain processes the actions that it could have taken to have a more favorable outcome. The region of the brain that codes for a favorable reward, the orbitofrontal cortex (OFC), is also involved in processing regret behavior. Although regret was considered a human emotion, it was recently discovered that the feeling of regret may prevail across other species too!
While studying the reward mechanisms in rats, a research team from the University of Minnesota noticed that rodents also exhibit the human-equivalent of regret in decision-making. This observation led them to devise a clever behavior task to test regretful decision-making in rats. Aptly named the Restaurant Row task, this set-up replicated the real-life situation of choosing between options of restaurants, except that it was tailored towards rats. It consists of a central loop extending into four arms. Each arm serves as a “restaurant zone” where the rat is supplied with different flavors of food pellets: banana, cherry, chocolate or plain (unflavored). Just as humans have a personal fondness for certain cuisines, the rats preferred certain flavors, determined by the amount of time they were willing to wait for that particular flavor (longer waiting times meant higher preference). The research team crafted a way to signal to the rats their ‘waiting time,’ much like we’d see a line waiting outside a restaurant. By sounding a tone as a “wait” indication, higher waiting times were indicated by higher tone pitches, and the count-down was performed by slowly lowering the pitch of the tone.
Based on its preferences, the rat decides whether a certain flavor was worth the wait and remained at a particular “restaurant zone,” or simply moved on to the next option. What the rat was unaware of was that there could be an equal or longer waiting time for the next not-so-preferred flavor! This is similar to the times when we might storm out of our favorite restaurant, upset by its insanely long waiting line, only to find ourselves waiting longer at a less preferred diner! Much like us humans, the rats too, when encountered by a situation where the second outcome seems evidently less favorable showed regret! Behaviorally, regret was identified when the rats would pause and look back at the previously lost option, potentially the what-could-have-been in the task. It is interesting to note that when the rats did receive their favorable flavor, they spent several seconds in the arm even after getting their reward, but in a regret-inducing decision, the rats would rush through their un-preferred meal and scurry away to the next “restaurant.”
All along this Restaurant Row task, the researchers recorded neuronal activity from the reward-associated regions of OFC and the ventral striatum. Some neurons fired upon receipt of the favorable flavor food, say, cherry (reward-responsive), while some others fired merely upon entry into the preferred “restaurant” i.e. cherry zone (zone-responsive). In a regret-inducing outcome, the rat left the cherry arm, and moved on to, say, the banana zone. Regretting its decision, as the rat looked back at the cherry zone, the researchers noticed that the zone-responsive neurons fired in the banana zone during the look-back in much the same way as during entry into the cherry zone. There was very little representation of the reward-responsive neurons (cherry) in comparison to the zone-responsive neurons (cherry zone). This means that while the rat is neuropsychologically processing regret, it regrets its actions more than the outcome itself.
This study illuminates a behavioral similarity between humans and rats, a parallel that gives hope to future studies that aim at using animal models to understand human behavior.
Steiner A.P. (2014). Behavioral and neurophysiological correlates of regret in rat decision-making on a neuroeconomic task, Nature Neuroscience, 17 (7) 995-1002. DOI: http://dx.doi.org/10.1038/nn.3740
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