There is now a great deal of evidence that people with depression show differences in processing rewards and punishments. How the brain learns to obtain rewards and avoid punishments is known as ‘Reinforcement Learning’ (RL). Studying RL in depression may help us understand this better.
Two key groups of neurotransmitters targeted by antidepressant treatments are involved in RL. These are Serotonin, targeted by the SSRIs and the catecholamines (Dopamine and Noradrenaline), targeted by Bupropion, an antidepressant widely used outside the UK and of similar efficacy to SSRIs. These two classes of drugs affect different components and aspects of RL. Broadly speaking, Bupropion appears to alter reward and effort processing while SSRIs (such as escitalopram) appear to alter sensitivity to loss. It seems likely that different classes of medication work for some people, but not for others. Currently there is no way to predict who will respond to which type of antidepressant.
Exploring the different impacts of these drugs on RL in depressed people will help to establish whether measures of RL could be used to predict who will respond to which sort of medication and give us a better idea of how antidepressants work.