Neural reward processing under dopamine agonists: imaging

Impulse control disorders (ICDs) are increasingly reported as a considerable side-effect of treatment with dopaminergic medication (both levodopa and dopamine agonists (DA)). ICDs together with punding are described within the entity of dopamine dysregulation syndrome along with immediate reward seeking and addictive behaviors. The brain functions involved in reward processing in general and their modulation by medication can be characterized by neuropsychological assessments and underlying neurobiology can be investigated by functional neuroimaging techniques such as functional magnetic resonance imaging (fMRI) or positron emission tomography (PET). By this approach, functional changes of brain areas involved in reward processing under short-term or chronic DA therapy were studied. Functional changes in a network involving striatal-thalamic loops, key structures of the reward system, together with limbic areas (such as the amygdala) and the ventral tegmental area could be related to pharmacological alterations of reward processing by dopaminergic medication. In particular, altered ventral striatal functioning seems to relate to ICDs such as pathological gambling. A general medication effect in patients under DA in terms of a sensitization toward ICD could be demonstrated. A synopsis is given on the applications of functional neuroimaging to investigate reward processing and the influence of dopaminergic medication.