AbstractCues, or stimuli in the environment, attain the ability to guide behavior via learned associations. As predictors, cues can elicit adaptive behavior and lead to valuable resources (e.g., food). For some individuals, however, cues are transformed into incentive stimuli and can elicit maladaptive behavior. The goal-tracker/sign-tracker animal model captures individual differences in cue-motivated behaviors, with reward-associated cues serving as predictors of reward for both goal-trackers and sign-trackers, but becoming incentive stimuli only for sign-trackers. While these distinct phenotypes are characterized based on Pavlovian conditioned approach behavior, they exhibit differences on a number of behaviors of relevance to psychopathology. To further characterize the neurobehavioral endophenotype associated with individual differences in cue-reward learning, we investigated neuroendocrine and behavioral profiles associated with negative valence in male goal-trackers, sign-trackers, and intermediate responders. We found that baseline corticosterone increases with Pavlovian learning, and that this increase is positively associated with the development of sign-tracking. We did not observe significant differences between goal-trackers and sign-trackers in behavior during an elevated plus maze or open field test, nor did we see differences in the corticosterone response to the open field test or physiological restraint. We did, however, find that sign-trackers have greater glucocorticoid receptor mRNA expression in the ventral hippocampus, with no phenotypic differences in the dorsal hippocampus. These findings suggest that goal-trackers and sign-trackers do not differ on indices of negative valence; rather, differences in neuroendocrine measures between these phenotypes can be attributed to distinct cue-reward learning styles.Significance StatementWhile the goal-tracker/ sign-tracker animal model derives from individual differences in Pavlovian conditioned approach behavior, other traits, including some of relevance to addiction and post-traumatic stress disorder, have been shown to co-exist with the propensity to sign-track. The extent to which this model encompasses differences in negative valence systems, however, remains largely unexplored. Here we show that behavioral and corticosterone response to paradigms associated with negative valence do not differ between goal-trackers and sign-trackers; but baseline corticosterone levels appear to be linked to the development of sign-tracking, as do differences in glucocorticoid receptor expression in the ventral hippocampus. These findings suggest that neuroendocrine measures typically associated with negative valence may, in fact, play an important role in positive valence systems.
Modelling Individual Differences in the Form of Pavlovian Conditioned Approach Responses: A Dual Learning Systems Approach with Factored Representations
