Abstract
Laboratory rats can exhibit marked, qualitative individual differences in the form of acquired behaviors. For example, when exposed to a signal-reinforcer relationship some rats show marked and consistent changes in sign-tracking (interacting with the signal; e.g., a lever) and others show marked and consistent changes in goal-tracking (interacting with the location of the predicted reinforcer; e.g., the food well). Here, stable individual differences in rats’ sign-tracking and goal-tracking emerged over the course of training, but these differences did not generalize across different signal-reinforcer relationships (Experiment 1). This selectivity suggests that individual differences in sign- and goal-tracking reflect differences in the value placed on individual reinforcers. Two findings provide direct support for this interpretation: the palatability of a reinforcer (as measured by an analysis of lick-cluster size) was positively correlated with goal-tracking (and negatively correlated with sign-tracking); and sating rats with a reinforcer affected goal-tracking but not sign-tracking (Experiment 2). These results indicate that the observed individual differences in sign- and goal-tracking behavior arise from the interaction between the palatability or value of the reinforcer and processes of association as opposed to dispositional differences (e.g., in sensory processes, “temperament,” or response repertoire).
Highlights
Laboratory rats can exhibit marked, qualitative individual differences in the form of acquired behaviors
The results of Experiment 1 confirm that our procedure produces marked individual differences in sign-tracking and goal-tracking
The unique feature of the results is that these differences were specific to a given signal-reinforcer relationship: sign-tracking on the left lever was unrelated to sign-tracking on the right lever and goal-tracking during the left lever was unrelated to goal-tracking on the right lever
Summary
Laboratory rats can exhibit marked, qualitative individual differences in the form of acquired behaviors. The qualitative individual differences in how learning is expressed that were described above (e.g., Fitzpatrick et al, 2013) are left unexplained by associative models of Pavlovian learning (e.g., Mackintosh, 1975; Pearce & Hall, 1980; Rescorla & Wagner, 1972) According to such models, the predictive relationship between the lever and the delivery of food should result in the formation of a link or association between the representations of the two allowing future presentations of the lever to activate a memory of food. This analysis allows that the exact form of conditioned response might not mimic the specific nature of the response to food itself (Wagner & Brandon, 1989), but they offer
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