Individual differences in cue valuation, decision-making, and response to dopamine treatment
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After multiple pairings of a cue and a rewarding event, animals will begin to attend to both the reward and the cue. Reports from Brown and Jenkins (1968) first described pigeons that began to track key lights predictive of food reward. Subsequently the phenomenon of conditioned cue approach has been reported across a variety of species including pigeons, quail, rats, monkeys, and stickleback fish (Brown and Jenkins, 1968; Cetinkaya and Domjan, 2006; Holland, 1977; Jenkins and Rowland, 1996; Sidman and Fletcher, 1968). More recently, investigations of individual differences in the expression of these behaviors have begun, as well as exploration into how these differences relate to other cognitive and neurological variations (Lesaint et al., 2014; Lovic et al., 2011; Meyer et al., 2012; Paolone et al., 2013). The objective of this dissertation was to characterize individual differences in rats’ propensity for orienting towards a light-cue predictive of reward. I also aimed to describe how these differences related to the behavior’s vulnerability to memory updating, extinction learning, a variety of cognitive functions, and behavioral and neurological responses to drug challenge. I report that all rats showed conditioned approach toward the site of food-reward delivery, but only a subset also showed robust rearing and/or orienting toward a light predictive of food (Orienters). Those rats that showed only conditioned reward approach were termed Nonorienters. Following memory update procedures, Orienters were more likely than Nonorienters to attenuate conditioned food approach, though conditioned rearing remains unaffected. Orienters were also more likely to make impulsive and risky decisions, enter a novel and risky environment, and be distracted during an attention assay. They also emitted more ultrasonic vocalizations than Nonorienters when exposed to amphetamine. Moreover, while both Orienters and Nonorienters preferred a context previously paired with drug to a context paired with saline, Orienters emitted more ultrasonic vocalizations during the preference test. Finally, while Orienters and Nonorienters showed behavioral differences after amphetamine injection, these differences were not reflected in the activity of the brain regions responsible for the conditioned orienting response. Overall, these findings suggest that Orienters are more apt to memory update, make more impulsive and risky decisions, are more vulnerable to distraction, and that amphetamine has more impact upon the behavior of Orienters.