reinforcement learning accounts of the ERN, prediction error in the dACC is directly related to ERN amplitude (Holroyd & Coles, 2008). Failure to find an association between DRD4 and dACC activity throws the finding of association between DRD4 and ERN into doubt. Of course, it may turn out that the DRD4 receptor gene or another of the commonly studied candidate genes influences ERN amplitude. However, the history of candidate gene research leads us to be cautious. In addition, early attempts to identify specific molecular-genetic influences on substance abuse also focused on dopamine genes because so many substances of abuse influence dopaminergic activity. For the most part, these efforts did not bear fruit. We should be wary of falling into the trap of thinking that simply because a phenotype seems to be related to dopaminergic activity that the traditional candidate dopamine genes are certain to contain its molecular genetic secrets. We encourage researchers interested in the ERN and other endophenotypes to be more catholic in their approach to the problem of identifying molecular genetic variants, and to look beyond the usual candidates (see section 10.3).
