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It has become a byword for bad behaviour. But it seems the rat may not be as heartless as we think.

Research shows that the rodents are capable of regret.

U.S. scientists trained rats to play a game called Restaurant Row, in which four food dispensers were laid out in a circle.

Capable of regret: U.S. scientists have discovered that rats may not be as heartless as we think (file picture)

The 'restaurants' dispensed foods of different flavours and when a rat came near, a tone was played that signalled how long they would have to wait to be fed.

The animals learnt which of the four sections had their favourite flavour and also knew that if they hung around too long by one dispenser, they would miss out on the food on offer elsewhere.

During the study, some of the rats did not wait for a tasty treat, then discovered they would have to wait even longer for something less appealing at the next dispenser.

In this case, they turned and looked back at the missed opportunity, researchers found.

The rodents were also more likely to wait longer at this second dispenser and then wolf down the food when it was dispensed.

Active: A brain region called the orbitofrontal cortex, that is active when humans feel regret (pictured in green), lit up when the rats looked back at a missed opportunity, the University of Minnesota researchers found

These, the University of Minnesota researchers say, are all features of regret.

Scientists also found a brain region called the orbitofrontal cortex, that is active when humans feel regret, lit up when the rats looked back at what might have been.

Regret was defined as the rats realising they had made a mistake – and that if they had chosen differently, they would have been better off.

This differs from disappointment, in which while things are worse than we would like them to be, it is not our fault.

The study, detailed in the journal Nature Neuroscience, is the first to show that an animal is capable of regret, an emotion once thought to be uniquely human.