It is also possible that the markedly attenuated sign tracking seen in adolescents relative to adults could reflect in part age differences in stimulus selection and cue learning propensities. For instance, in a passive avoidance task, an older study found that adolescent rats were less disrupted by a change in a redundant discriminative cue, while more disrupted by a contextual change than younger or older rats (Barrett et al., 1984). In recent work, less cue-induced reinstatement of drug intake was seen in rats trained to self-administer cocaine or morphine in adolescence compared to animals that initiated drug use as adults (Doherty et al, 2009, Li & Frantz, 2009), data also commensurate with the suggestion that adolescents may perhaps attribute motivational salience to stimuli differently than do adults. Clearly, more research is needed to resolve the issue of how adolescents differ from adults in their attribution of incentive salience for rewards and for cues predicting those rewards, as well as to determine the potential implications of these developmental differences for the adolescent-associated propensity to use and sometimes abuse drugs and alcohol.
