Rats experience regret when their actions make them miss out on better food options, a study has found.
It is the first time regret has been identified in mammals other than humans.
Researchers created situations where rats had to choose whether to wait a set amount of time for a food reward, or move onto another one.
Those that moved on and found the next offering was even worse showed regretful behaviour.
The study was conducted by neuroscientists based at the University of Minnesota, US; their findings are reported in Nature Neuroscience.
If the line is too long at the Chinese restaurant, then you give up and go to the Indian restaurant across the street'
End Quote Prof David Redish University of Minnesota
It suggests thoughts similar to regret can affect the future decisions rodents make and dispels the belief that regret is unique to humans.
Prof David Redish, from the US-based research team, said it was important to differentiate regret from disappointment.
'Regret is the recognition that you made a mistake, that if you had done something else, you would have been better off,' he said.
'The hard part was that we had to separate disappointment, which is just when things aren't as good as you hoped. The key was letting the rats choose.'
They developed a task called Restaurant Row, in which rats decided how long they were willing to wait for different foods during a 60-minute run.
'It's like waiting in line at the restaurant,' Prof Redish. 'If the line is too long at the Chinese restaurant, then you give up and go to the Indian restaurant across the street.'
The rats waited longer for their preferred flavours, meaning the researchers could determine good and bad food options.
Occasionally the rats decided not to wait for a good option and moved on, only to find themselves facing a bad option - the scientists called this a regret-inducing situation.
In these cases the rats often paused and looked back at the reward they had passed over.
They also made changes in their subsequent decisions, being more likely to wait at the next zone and rushing to eat the reward that followed. The scientists say such behaviour is consistent with the expression of regret.
When experiments were carried out where the rats encountered bad options without making incorrect decisions, such behaviour was not present.
'In humans, a part of the brain called the orbitofrontal cortex is active during regret. We found that in rats recognising that they made a mistake, their orbitofrontal cortex represented the missed opportunity,' Prof Redish said.
'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.'
Prof Redish believes that this animal model of regret could now be used to help understand how regret affects the decisions humans make.
Dr Mark Walton, from the University of Oxford, who reviewed the research, said the findings were significant as they showed a high level of cognitive ability in rats and also praised the team's experiment.
'It is a clever way to look at cognitive processes, seeing how rats perform these tasks can open up how they think and behave in the wild,' he said.
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