Dopamine DRD2 Polymorphism Alters Reversal Learning and Associated Neural Activity

In humans, presence of an A1 allele of the DRD2/ANKK1-TaqIa polymorphism is associated with reduced expression of dopamine (DA) D-2 receptors in the striatum. Recently, it was observed that carriers of the A1 allele (A1 + subjects) showed impaired learning from negative feedback in a reinforcement learning task. Here, using functional MRI(fMRI), we investigated carriers and noncarriers of the A1 allele while they performed a probabilistic reversal learning task. A1 + subjects showed subtle deficits in reversal learning. In particular, these deficits consisted of an impairment in sustaining the newly rewarded response after a reversal and in a generally decreased tendency to stick with a rewarded response. Both genetic groups showed increased fMRI signal in response to negative feedback in the rostral cingulate zone (RCZ) and anterior insula. Negative feedback that incurred a change in behavior additionally engaged the ventral striatum and a region of the midbrain consistent with the location of dopaminergic cell groups. The response of the RCZ to negative feedback increased as a function of preceding negative feedback. However, this graded response was not observed in the A1 + group. Furthermore, the A1 + group also showed diminished recruitment of the right ventral striatum and the right lateral orbitofrontal cortex (lOFC) during reversals. Together, these results suggest that a genetically driven reduction in DA D-2 receptors leads to deficient feedback integration in RCZ. This, in turn, was accompanied by impaired recruitment of the ventral striatum and the right lOFC during reversals, which might explain the behavioral differences between the genetic groups.