DRD1 and DRD2 genotypes modulate processing modes of goal activation processes during action cascading

Dopamine plays an important role in action selection, but little is known about the influence of different dopamine receptor systems on the subprocesses occurring during the cascading of actions. Because action selection and cascading can be accomplished in a serial manner or a parallel manner, we investigated the potential effects of DRD1 (rs4531) and DRD2 (rs6277) receptor polymorphisms on this dimension. We gathered behavioral and neurophysiological data from healthy human subjects (n = 162) and applied mathematical constraints to quantify their action selection strategy on a serial-parallel continuum. The behavioral results show a more serial and more effective action cascading strategy in homozygous DRD1 G allele carriers, who are assumed to have a higher D1 receptor efficiency than carriers of the A allele. In the group of homozygous DRD2 T-allele carriers, who have a higher striatal density of D2 receptors than C-allele carriers, we found a less effective and more parallel action cascading strategy. These findings suggest that, within the same sample, a higher D1 efficiency seems to shift the action cascading strategy toward a more serial processing mode, whereas the D2 receptors seem to promote a shift in the opposite direction by inducing a more parallel processing mode. Furthermore, the neurophysiological analysis shows that the observed differences are not based on attentional differences or basic inhibition. Instead, processes linking stimulus processing and response execution seem to differentiate between more serial and more parallel processing groups.