We like to think that our more complex emotions are uniquely human, although researchers continually thwarting that belief with science. This week, another of our emotions came under threat – regret. Nobody has ever demonstrated regret in another non-human animal. Until now. A study released this month in Nature claims to have found evidence that rats are capable of feeling regret, a complex emotion distinct from mere disappointment.
Disappointment is when we recognise that we didn’t get as much as we expected, whereas to regret is to recognise that our actions are the reason behind this – that an alternative action, a different decision, would have produced a better outcome. In this study, researchers forced rats to choose between waiting for a particular reward, or moving onto the next reward that may come with an even longer wait. This is exactly the type of situation we might expect rats to feel regretful about, but are they smart enough to feel such a complex emotion?
Psychologists say that regret should be characterised by immediate behavioural and neurophysiological changes that reflect the missed opportunity, as well as longer-term changes to behaviour. In humans, regret is thought to be dealt with in the orbitofrontal cortex (OFC), an area that is particularly active when we feel regretful, and which when damaged leaves patients unable to feel regret. This region has been previously shown to be important in assessing and understanding rewards in non-human animals including rats. Another area of the brain, the ventral striatum (vStr), is thought to be involved in evaluating the outcomes of our actions.
The researchers recorded behavioural responses and activity of neural ensembles (groups of neurones) in the OFC and vStr in rats during a reward task involving patience. Rats were trained to play ‘Restaurant Row’, a foraging game which placed them in the centre of a circular area with four ‘zones’. Each zone led to a path which ended in a reward of a different flavour. Think ludo, if that description seemed confusing! When a rat entered a particular zone, a tone would sound indicating the beginning of a countdown to the reward (food) being presented. A higher-pitched tone indicated a longer wait, with the sounds counting down in pitch until the reward was available. Rats could choose to wait for the reward, or if they stepped out of the zone they were considered to have ‘skipped’ that option and a countdown would begin at the next zone. The length of each wait was calculated at random, somewhere between 1 and 45 seconds, and each time a rat entered a new zone a new wait would be calculated. Rats prefer different flavoured foods, so each zone contained a reward of a different ‘value’, the ‘cost’ of the reward being the wait time. Rats quickly developed a threshold for waiting for each flavour – “I’d be prepared to wait 15 seconds for chocolate, but only 8 seconds for Cherry”. Rats were allowed to roam freely around restaurant row for a full hour, while the researchers monitored their brains and behaviour.
After the experiment was complete, the researchers looked at a very specific set of results – they were interested in the behaviour and neurophysiology of the rats in cases where they had first skipped a zone even though the wait time was lower than their threshold for that flavour, and then been offered a wait time longer than their threshold on the next zone. They compared the rats behaviour and brain activity in this type of regretful situation with other situations that would merely be disappointing. For example, comparing between situations where the rat skipped a high-value reward and was met with a low-value reward (regret) and situations where the rat waited for the first high-value reward and was then met with a low-value reward at the next zone (disappointment), allowed the researchers to distinguish between the two options.
What the researchers found suggests that rats are indeed capable of experiencing the complex emotion of regret. Rats in regret-inducing situations would pause and look back at the skipped reward, whereas rats in disappointing situations tended to look either at the current reward, or forward onto the next zone. Likewise, regretful rates showed neurophysiological activity patterns in the OFC and vStr that represented the missed opportunity, but this pattern was not found in disappointed rats. Finally, past regret seemed to influence their future behaviour – rats that had experienced regret were more likely to accept long-wait times for rewards, and gobbled up the reward eagerly when it finally arrived.
Want to Know More?
Steiner and Redish (2014) Behavioral and neurophysiological correlates of regret in rat decision-making on a neuroeconomic task. Nature Neuroscience
Featured image used under a creative commons licence from wikimedia commons. Original image by AlexK100