The Neural Correlates of Acquiring and Updating Reward Value

The decision to pursue a reward is influenced by how one values the reward. It is therefore adaptive to be able to determine reward value as well as recognize changes in reward value and update behavior accordingly. Delineating the neural systems that underlie how reward value is acquired and updated will advance the understanding of reward-based decisions. In the first project of my thesis, I aimed to determine how temporal delays can update reward preference. To address this, I utilized a non-contingent training paradigm to deliver rewards at different temporal intervals. I performed pharmacological manipulations or site-specific lesions to determine the neural regions required for preference to update. My findings suggest that temporal costs can enhance the preference for a less desirable reward option, and that this change in preference requires the basolateral amygdala and retrosplenial cortex. In the second project, I examined the neural signals that are thought to be involved with learning about reward value. The dopamine system encodes differences in reward value in well-trained animals. However, it is unclear how reward value is acquired by the dopamine system in early learning. To address this, I utilized a Pavlovian conditioning task in which distinct cues predicted rewards of different sizes. I performed fast-scan cyclic voltammetry to record changes in dopamine release in the nucleus accumbens of male and female rats throughout early learning. My findings demonstrate sustained sex differences in behavioral responding as well as transient sex differences in reward-evoked dopamine release. In the final project of my thesis, I examined how dopamine signaling regulates to behavioral responses during different phases of training on Pavlovian conditioning task. Differences in dopamine release across early and late training suggest that the dopamine system differentially regulates behavioral responding across training. To address this, I utilized two distinct Pavlovian paradigms in which cues signal either rewards delivered at different rates, or rewards or different sizes. I performed pharmacological manipulations and determined dopamine's regulation over a given behavior depends upon the level of prior training the subject received as well the reward-related information conveyed by the cues. Together, I describe the neural correlates of acquiring and updating reward value.