Crib-biting horses were recently shown to exhibit increased activity within the mesoaccumbens dopamine pathway (McBride and Hemmings 2005). Given the multi-factored functionality of the mesoaccumbens system, this alteration in dopamine physiology may have an effect on other aspects of the behavioural repertoire. For instance, in experiments which sought to ascertain the function of the nucleus accumbens in extinction learning, nucleus accumbens dopamine efflux decreased in a linear fashion following unrewarded operant responses, whilst exitotoxic (ibotenic acid) lesions of the nucleus accumbens had the ability to impair response extinction (Ichikawa et al. (2004). Thus, a role for this brain region in extinction learning is certainly implicated. The aim of this study was to determine if facilitated accumbens dopamine transmission affects learning characteristics in the horse. From the aforementioned discussion it was hypothesised that enhanced accumbens dopamine transmission would potentially delay the linear reduction in dopamine release associated with extinction of an operant response. Or, from a functional perspective, cause heightened salience of a conditioned stimulus thereby delaying the onset of extinction learning.