Do rewards change an animal's emotional state?

It is well established that punishing or threatening events lead to long lasting negative emotional (affective) states in animals, such as fear, anxiety and even depression. Improving the welfare of managed animals predominantly focuses on understanding what factors cause negative emotional states, so that they can be reduced or removed. However, widely accepted theoretical frameworks suggest that an animal's long-term emotional state will be shaped not just by negative experiences, but also by positive experiences of rewarding events (i.e. through their cumulative experience). These theories have yet to be tested, and the idea that positive events can improve emotional state is largely unexplored. Therefore, the big question remains: do rewarding stimuli and events actually change an animal's emotional state, such as reducing anxiety or depression, and so can rewards be used to improve animal welfare?
Some studies in humans suggest that this could be the case. For example, there are longitudinal studies suggesting that recent positive events can increase how people subjectively rate their welfare, and some therapies for alleviating depression are based upon people experiencing positive emotions. In addition, the experience of positive emotions can also reduce stress reactivity and increase resilience in humans, suggesting that positive emotions may also bring mental and physical health benefits. Given that few studies have yet addressed these potential benefits in animals, it is important to know if and how rewards impact on animals' emotions in order to develop effective and practical interventions to improve animal welfare, whether for farm, laboratory or companion animals.
The aims of the project will be to:
1. Establish short and longer term impacts of reward schedules on animal emotional states
2. Compare the effectiveness of two different types of reward - social and nutritional - for improving emotional state
3. Assess whether rewards can help reduce stress reactivity, increase resilience to future negative events and increase physical as well as emotional well-being.
Using mice as a model species, we can use a very simple method to experimentally manipulate their emotional state: mice picked up by their tails are consistently in a more negative state than those handled using non-aversive methods (see publications). To assess emotional state, we will measure behavioural patterns in the home cage, and responses in standard validated tests of anxiety (e.g. Open Field Test, Elevated Plus Maze), depression (sucrose consumption) and a novel operant test of pain perception (Orofacial Pain Asssay). We will then look at how different types of rewards (social or nutritional) and reward schedules can positively impact emotional state. Responsiveness to standard stressors will be assessed using measures of both spontaneous and operant behavioural responses, and physiological responses (such as plasma corticosterone levels, pain scoring and avoidance behaviour).