Rats May Be Pessimistic Too

Rats housed in unpredictable conditions appear to have a more negative outlook than those housed in stable, settled conditions, according to new research by scientists at Bristol University Veterinary School, published in this week’s issue of Nature.

The researchers found that whether an animal anticipates that something good or bad is going to happen can provide a clue as to the emotion it may be experiencing. Emma Harding, Liz Paul and Mike Mendl from the Centre for Behavioural Biology at Bristol University consider the research offers a new way for measuring the emotional states of animals, and will help scientists better understand the effects of housing conditions on animal emotion and welfare, so allowing the design of more welfare-friendly animal housing.

“It is very important that we develop good methods for estimating emotional experiences in animals because they are crucial to our understanding of animal welfare. Although we cannot know for certain what emotions are being experienced by other animals, our technique offers a promising new approach,” said Dr Mendl.

Previous research has shown that anxious and depressed people tend to expect bad things to happen – they see the glass as half empty rather than half full – while the opposite is true for happy people. The Bristol team have developed a new technique for investigating whether this is also the case in animals.

Rats were trained that a sound of a particular pitch predicted a good event – the arrival of food – and that another sound of a different pitch predicted a bad event – no food and a short noise. They were then presented with sounds of intermediate pitch to see whether they treated these ambiguous sounds as indicating the good or bad event. Rats kept in unpredictable housing conditions were less likely to treat these sounds as heralding the arrival of the good event than were those housed in stable environments.

“Their judgements show parallels with the negative outlook seen in some depressed people, suggesting that a disrupted home life also disrupts their mood state,” said Dr Harding.

Dr Paul further explained how “Studies have shown that anxious people seem to be particularly on the look out for negative and threatening things, even at a subconscious level. We now have evidence that other animals may behave in a similar way and this is an important finding for animal welfare.”