Catechol-O-methyltransferase val158met genotype influences neural processing of reward anticipation

Reward processing depends critically on dopaminergic neurotransmission in the ventral striatum. The common polymorphism val158met of catechol-O-methyltransferase (COMT) accounts for significant interindividual variations in dopamine (DA) degradation, although the direct effect of COMT on striatal DA might be limited. Using fMRI we assessed the influence of COMT val158met genotype on brain activations elicited by the anticipation of monetary gains and losses in forty-four healthy volunteers. We found that the met158 allele, which is presumably linked to higher synaptic DA levels, was associated with higher responses in ventral striatum to loss incentives. There was a linear relationship between the number of met158 alleles and ventral striatal activity. Furthermore, we observed a similar gene-dose effect in the anterior temporal cortex, a region that has been linked to the coupling of sensory information with emotional contents. Temporal cortex also showed enhanced connectivity to the ventral striatum during the processing of incentive stimuli. Increased ventral striatal reactivity to loss incentives related to the met158 allele might contribute to the observed association of the met158 allele to higher loss aversion behaviour. Current evidence and our results are compatible with an interpretation that construes this effect of COMT genotype on striatal reactivity as a result of a cortico-striatal interaction.