P rats showed deficits in a passive avoidance learning task, in which the rats had to learn to inhibit stepping down from a platform to avoid a shock. In addition, they showed deficits on a DRL task, in which they had to learn to suppress bar pressing when training was shifted to require a delay in bar pressing to receive a sugar pellet reward. This led the researchers to suggest that P rats are ‘a good model of disinhibitory processes associated with familial and personality-risk for alcoholism’ (Steinmetz et al. 2000). Research using the high alcohol drinking (HAD1 and HAD2) and low alcohol drinking (LAD1 and LAD2) rat lines indicate that animals selected for high alcohol consumption also exhibit higher levels of delay aversion measured using a delay discounting task (Wilhelm & Mitchell 2008). Conversely, rat and mouse strains have been selectively bred for divergence in novelty seeking, as measured based on levels of exploratory locomotion in a novel environment, which provides evidence that this is a heritable trait (Kliethermes & Crabbe 2006). However, selective breeding for delay aversion or response inhibition has not occurred, presumably due to the complex nature of the tasks used to generate these behaviors and
