Blocking in autoshaped lever-pressing procedures with rats

Abstract

Rats will approach and contact a lever whose insertion into the chamber signals response-independent food delivery. This “autoshaping” or “sign-tracking” phenomenon has recently attracted considerable attention as a platform for studying individual differences in impulsivity, drug sensitization, and other traits associated with vulnerability to drug addiction. Here we examined two basic stimulus selection phenomena, blocking and overshadowing, in the autoshaped lever-pressing of rats. Blocking and overshadowing were decidedly asymmetrical. Previously reinforced lever-extension conditioned stimuli (CSs) completely blocked conditioning to auditory cues (Experiments 1 and 2), and previously nonreinforced lever-extension CSs overshadowed conditioning to auditory cues. By contrast, conditioning to lever-extension CSs was not blocked by either auditory (Experiment 3) or lever insertion (Experiment 4) cues, and was not overshadowed by auditory cues. Conditioning to a lever insertion cue was somewhat overshadowed by the presence of another lever, especially in terms of food cup behavior displayed after lever withdrawal. We discussed several frameworks in which the apparent immunity of autoshaped lever-pressing to blocking might be understood. Given evidence that different brain systems are engaged when different kinds of cues are paired with food delivery, it is worth considering the possibility that interactions among them in learning and performance may follow different rules. In particular, it is intriguing to speculate that the roles of simple cue-reinforcer contiguity as well as of individual and aggregate reinforcer prediction errors may differ across stimulus classes.

Isolating the incentive salience of reward-associated stimuli: value, choice, and persistence

“…Like others (Holland 1977;Cleland and Davey 1983;Holland et al 2014;Meyer et al 2014) the present results demonstrate clearly that different conditioned stimuli can preferentially elicit sign-and goal-tracking, and these stimuli can be differentially attributed with incentive salience or value. However, the current within-subject method is a departure from the predominant method used to study sign-and goal-tracking behavior in the past.…”

“…Holland et al 2014), an issue that may be partially related to differences in animal vendors or even breeding colonies within vendors (Fitzpatrick et al 2013). Furthermore, because identification of the response cohorts is based on PCA performance, study of the processes involved in the acquisition of sign-and goal-tracking behavior is problematic; although the use of a genetic model has been used for the study of sign-and goal-tracking response acquisition (Flagel et al 2011), selective breeding comes with its own set of problems (e.g., inadvertent neurobehavioral changes not intentionally selected).…”

“…For example, others that have measured multiple response types to the tone with video, including rearing/orienting and head-jerk responses, but these studies have repeatedly demonstrated that a tone CS preferentially elicits goal-tracking behavior, regardless of the relative location of the tone source to the food magazine (Holland 1977;Harrison 1979;Cleland and Davey 1983;Holland et al 2014;Meyer et al 2014); moreover this goal-tracking to a tone is not due to an inability of animals to localize the tone source, as sign-tracking responses to a tone are subject to reinforcement (Harrison 1979;Cleland and Davey 1983). Furthermore, under the present conditions, neither localizability nor stimulus modality of the reward-associated stimulus alone appear to be defining features necessary for sign-tracking, as a nosepoke stimulus that shared the visual modality and location of the lever produced predominant goal-tracking behavior (see Fig.…”

“…As with the cohort approach, all animals tested herein were exposed to PCA training with a lever, leading to the question of why there was so little goal-tracking observed to the lever in the present experiments. Others (Boakes 1977;Davey et al 1982;Chang et al 2012;Chang and Holland 2013;Chang 2014;Holland et al 2014) have observed a similar bias toward sign-tracking to a lever as that observed herein when training took place in conjunction with an additional control lever that was never followed by food (Lever2); consistent with this hypothesis, both sign-tracking rates to the lever and goal-tracking rates to the tone were higher in the 4-CS PCA experiment, where both stimuli were trained with a never-reinforced counterpart (Lever2 and Tone2). Additionally, Other than the single between-subject experiment presented herein (although no goal-trackers were identified in that experiment either), all animals were trained with at least one additional stimulus, leaving open the possibility that including any element of discrimination in training may promote sign-tracking to the food-associated lever (cf.…”

“…Interestingly, there is also a large literature demonstrating that pairing different stimuli (e.g., levers or tones) with reward can differentially induce signand goal-tracking. For example, pairing a tone with food results in primarily goal-tracking behavior (Holland 1977;Harrison 1979;Cleland and Davey 1983;Holland et al 2014;Meyer et al 2014). Furthermore, Meyer et al (2014) demonstrated that a reward-predictive tone that elicits goal-tracking behavior maintains the same amount of conditioned reinforcement in animals prescreened as sign-trackers or goal-trackers, while the lever stimulus associated with sign-tracking was the most robust conditioned reinforcer.…”