Abstract
When a cue is paired with reward in a different location, some animals will approach the site of reward during the cue, a behavior called goal tracking, while other animals will approach and interact with the cue itself: a behavior called sign tracking. Sign tracking is thought to reflect a tendency to transfer incentive salience from the reward to the cue. Adolescence is a time of heightened sensitivity to rewards, including environmental cues that have been associated with rewards, which may account for increased impulsivity and vulnerability to drug abuse. Surprisingly, however, studies have shown that adolescents are actually less likely to interact with the cue (i.e., sign track) than adult animals. We reasoned that adolescents might show decreased sign tracking, accompanied by increased apparent goal tracking, because they tend to attribute incentive salience to a more reward-proximal “cue”: the food magazine. On the other hand, adolescence is also a time of enhanced exploratory behavior, novelty-seeking, and behavioral flexibility. Therefore, adolescents might truly express more goal-directed reward-seeking and less inflexible habit-like approach to a reward-associated cue. Using a reward devaluation procedure to distinguish between these two hypotheses, we found that adolescents indeed exhibit more goal tracking, and less sign tracking, than a comparable group of adults. Moreover, adolescents’ goal tracking behavior is highly sensitive to reward devaluation and therefore goal-directed and not habit-like.
Highlights
Animals and humans vary widely in the degree to which they ascribe motivational value, or incentive salience, to reward-predictive cues
Sign tracking is represented by lever deflections and goal tracking by magazine entries during the 8 s lever/light cue, neither behavior is required for delivery of the sugar pellet reward after cue termination
Sign-tracking behavior, compared with goal-tracking behavior, is relatively insensitive to reward devaluation, whether accomplished via pre-feeding (Patitucci et al, 2016; Conrad and Papini, 2018) or conditioned taste aversion (CTA; Morrison et al, 2015; Smedley and Smith, 2018; devaluation can affect the approach to the cue under some circumstances: see Cleland and Davey, 1982; Derman et al, 2018)
Summary
Animals and humans vary widely in the degree to which they ascribe motivational value, or incentive salience, to reward-predictive cues. This variability can be measured using a Pavlovian conditioned approach (PCA) procedure in which a cue (e.g., extension of a lever) is followed by the delivery of a reward in a separate location. Under these circumstances, some animals will approach the location of reward delivery: a behavior known as goal tracking (Boakes, 1977). A growing body of evidence supports a relationship between sign tracking and certain maladaptive behaviors, including impulsive action (Lovic et al, 2011), initiation and maintenance of drug-taking (Flagel et al, 2009; Beckmann et al, 2011) and relapse after abstinence (Versaggi et al, 2016).
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