The influence of dopamine D2R-mediated signaling on reversal learning is also poorly understood. Reversal learning can be conceptualized as the ability to recognize an unexpected consequence to a previously established associative learning rule and then alter response strategies accordingly [17,18]. Reversal learning in rodents can serve as an index of learning adaptability and alertness that correlates with human attentional-shift paradigms [17,18]. Additionally, a previous report demonstrated that excitotoxic lesions of terminal field targets of mesocortical dopamine have been shown to disrupt reversal learning [19]. Administration of the D2R/D3R antagonist, sulpiride, impairs spatial reversal leaning in mice [20] and has also been shown to impair attention and the cognitive performances of healthy human volunteers [21]. Moreover an inverse relationship between lower dopamine D2R levels and compulsive behavior in human subjects has been reported [22]. Taken together these findings suggest that D2R-mediated signaling could play a critical role in reversal learning but are insufficient to prove it.