Processing rewards (e.g. food/water/social interactions) is a complex mechanism performed by most organisms for survival. Three main mechanisms involved in this include, generating the motivation to attain a reward, cognitive processes that enable learning about rewarding stimuli in the environment, and hedonic processes that generate feelings of pleasure from the reward. Deficits in reward processing are associated with a number of psychiatric disorders, including Major Depressive Disorder (MDD).

This review discusses how reward processing can be measured through rodent models, and how behaviours produced can be translated to symptoms seen in patients with MDD. We discuss potential evidence of the neurobiological mechanisms that could be contributing to the development of these symptoms, as based on preclinical studies in rodents, and we evaluate the breadth of behaviour tests thought to measure these three mechanisms of reward processing.

This paper provides an overview of the current developments in this field, and tries to emphasise the necessity for treating reward-related motivation, cognition and hedonia as separate behaviours, given evidence that these may potentially be driven by separate, but interacting, neurobiological networks. Furthermore, it is well known that there is poor treatment efficacy across patients with MDD, which could be influenced from such a variety of symptoms presenting in different patients (heterogeneity). Assessing mechanisms of reward processing and their neurobiology separately, as discussed in this review, could improve the way we model MDD in rodents and lead to improved treatment development that is targeted at the symptom-level rather than the disorder as a whole.

Lucy Lewis, SWBio DTP student

Review: Affective biases and their interaction with other reward-related deficits in rodent models of psychiatric disorders by Lucy R. Lewis, Abigail Benn, Dominic M. Dwyer and Emma S.J. Robinson in Behavioural Brain Research.