Individual Variation in the Motivational Properties of Reward Cues.

Abstract

Reward-associated stimuli are critically involved in the organization of behavior. Such cues, if they are attributed with incentive motivational properties, can act as incentive stimuli, with the power to evoke complex emotional and motivational states that drive reward-seeking behavior. Incentive stimuli can motivate behavior via multiple psychological processes, including attracting approach, reinforcing actions themselves, and/or spurring on new or ongoing behavior, and these processes rely on a distributed set of overlapping, but partially distinct brain systems. Critically, not only do cues guide adaptive reward seeking, they also contribute to compulsive disorders, such as addiction and binge eating. Importantly, there is substantial variation in the tendency of different individuals to assign motivational value to cues. Some rats (sign trackers), for example, find a discrete Pavlovian food-predictive cue attractive, in that it motivates approach behavior, and these animals will work avidly to obtain the cue. Other rats (goal trackers), alternatively, learn the cue’s association with food, but do not find the cue itself attractive, instead approaching the location of food delivery. Thus, reward cues only acquire incentive stimulus properties in some individuals. This may have broad implications for understanding variations in normal reward seeking as well the factors that contribute to differences in susceptibility to psychopathologies such as addiction. The primary goals, here, were to better understand the neural mechanisms responsible for this variation, and to establish the extent to which variation in food-cue responsivity predicts variation in behavior motivated by drug cues. In the experiments outlined here, I found that there are broad sign and goal-tracker differences in responsivity to different types of drug-related cues, reflecting fundamental variation in the psychological and neurobiological processes underlying cue processing. Additionally, dopamine signaling within the nucleus accumbens is critical for cues to produce conditioned motivation that drives reward seeking. Given that different animals exhibit sensitivity to different types of reward-associated information, there may be multiple “vulnerability” states underlying a variety of maladaptive patterns of behavior. Further exploration of the mechanisms underlying variation in responsivity to reward cues will provide a better understanding of the organization of adaptive reward seeking, as well as psychopathology.