RAPPORT DE STAGE D’OPTION SCIENTIFIQUE Rewards, Punishment and the Brain

This work is about interactions between facilitation and inhibition of behavioural responses. Generally, rewards elicit approach and are associated with facilitation of responses, whereas punishments elicit avoidance and inhibit behavioural responses other than fight or flight. Dopamine (DA) and serotonine (5HT) have been widely associated with respectively facilitatory and inhibitory regulation of behaviour, or approach and withdrawal. Dopamine facilitates action (drive effect), and reinforces action-outcome, stimulus-outcome and stimulus-response associations (learning effect). Serotonin generally inhibits reward-related responding, but can also facilitate it ; there being at least 14 subtypes of serotonin receptors allows for a vast range of complementary (and sometimes seemingly contradictory) effects. Serotonin and dopamine interact at the level of their numerous shared target areas in the brain, and serotonin also regulate dopamine at the level of cell bodies. The ambiguous influence of serotonin on the dopaminergic system parallels its effects on behaviour ; that is, generally inhibitory but sometimes excitatory. Punishment provides a context of increased interactions between approach and withdrawal, as well as serotonin and dopamine. Therefore, studying what happens during punishment can provide insight on the general meaning of these interactions. Here, we provide a model of behaviour during punishment and propose an interpretation in terms of neuromodulators. The core of the model is the hypothesis that the best way to cope during punishment is to dampen most rewards, while overemphasizing the effect of the spared ones ; coping strategies would thus be better implemented and learnt. Dopamine is attributed its usual facilitatory role on action, and serotonin is pictured as regulating approach and inhibition on a higher hierarchical level by carving dopamine function.