Directed approach responses and positive conditioned suppression in the rat

Effects of an ethanol-paired conditioned stimulus on responding for ethanol suppressed by a conditioned-taste-aversion

Ethanol-Paired Conditioned Stimuli (CS) can increase ethanol-responding either in extinction or occurring at low rates late in a session. To examine the generality of CS-induced increases in ethanol-responding, we examined whether a CS could increase responding suppressed by Conditioned-Taste-Aversion (CTA), which presumably suppresses responding by changing ethanol's valence from positive to negative. Rats were trained to respond for ethanol under a Random Interval (RI) schedule. We then removed the lever and paired Random-Time ethanol deliveries with illumination of a stimulus light (i.e., CS) for 10 sessions. Results were compared with a Truly Random Control group, in which the light and ethanol deliveries occurred independently. In a subsequent experiment, rats were treated similarly, except the light served as a discriminative stimulus, as the lever was extended and ethanol deliveries were available under a RI during light presentations. After this training, the lever was returned and rats again responded for ethanol. Subsequently, sessions were followed by LiCl administration. When responding reached low levels, LiCl administration stopped and the light was occasionally illuminated during the session. Responding during the light presentation was compared to responding during the period preceding light presentation. Responding partially recovered across 10 sessions and was greater during light presentations than in the period before it in all three groups. Increases were not reliably different between the groups, indicating that explanations for these increases such as CS-induced increases in motivation or approach toward the light are unlikely to be correct. The most likely explanation for these light-induced increases is that during sessions in which the light had been presented previously, LiCl had never been presented and thus, the light had come to signal that ethanol was safe to drink.

Enhancement of Food-Rewarded Instrumental Responding by an Appetitive Conditioned Stimulus

Four experiments are reported in which a stimulus (with a minimum duration of 60 s) signalling the delivery of “free” food was presented to rats lever-pressing for food available on a variable interval schedule. It was found that responding was enhanced in the presence of the stimulus when the baseline schedule of reinforcement was lean (Experiment I) and that the enhancement was dependent upon the pairing of the stimulus with free food (Experiments II and III). Experiment IV showed that an enhancement could be found after initial training in which stimulus-food pairings were given to subjects that were not concurrently lever pressing for food. It is argued that these results are consistent with the suggestion that an appetitive conditioned stimulus can energise appetitive instrumental behaviour.

Stimulus control of schedule-induced activity in pigeons during multiple schedules

Stimulus control of schedule-induced general activity was demonstrated with pigeons using multiple schedules of response-independent food delivery. In Experiment 1, the introduction of food during a multiple variable-time 30-second variable-time 30-second schedule produced a tenfold increase in activity above the no-food baseline. Each pigeon developed stable differential activity rates during the components (correlated with red and green lights) of a multiple variable-time 30-second extinction schedule. Lengthening the extinction component from 1 to 7 minutes increased the rate differences and produced a reliable pattern of responding during S- (the stimulus correlated with extinction): Activity rate was high immediately following the change from S+ (the stimulus correlated with variable-time 30-second) to S-, then decreased abruptly and remained low throughout the middle of the interval, and subsequently showed a positively accelerated increase until the stimulus changed to S+. In Experiment 2, three pigeons were exposed to a mixed variable-time extinction schedule prior to a multiple variable-time extinction schedule. Auditory rather than visual stimuli were used to determine the generality of Experiment 1 results. The multiple- versus mixed-schedule results indicated that stimulus control of activity occurred for two of the birds, but rate differences between S+ and S- were much less than those demonstrated with visual stimuli. A direct comparison of visual and auditory stimulus control in Experiment 3 supported this conclusion. These parallels between the stimulus control of reinforced responding and that of schedule-induced activity suggest that the stimulus control of induced activity may be a factor in operant stimulus control.

Effects of prior amphetamine exposure on approach strategy in appetitive Pavlovian conditioning in rats

RATIONALE

Pavlovian conditioning with a discrete reward-predictive visual cue can elicit two classes of behaviors: "sign-tracking" (approach toward and contact with the cue) and "goal-tracking" (approach toward the site of reward delivery). Sign-tracking has been proposed to be linked to behavioral disorders involving compulsive reward-seeking, such as addiction. Prior exposure to psychostimulant drugs of abuse can facilitate reward-seeking behaviors through enhancements in incentive salience attribution. Thus, it was predicted that a sensitizing regimen of amphetamine exposure would increase sign-tracking behavior.

OBJECTIVE

The purpose of these experiments was to determine how a regimen of exposure to amphetamine affects subsequent sign-tracking behavior.

MATERIALS AND METHODS

Male Long-Evans rats were given daily injections of d-amphetamine (2.0 mg/kg) or saline for 5 days, then given a 7-day drug-free period followed by testing in a Pavlovian conditioning task. In experiment 1, rats were presented with a visual cue (simultaneous illumination of a light and extension of a lever) located either to the left or right of a centrally located food trough. One cue (CS+) was always followed by food delivery, whereas the other (CS-) was not. In experiment 2, rats were tested in a nondiscriminative (CS+ only) version of the task.

RESULTS

In both experiments, amphetamine-exposed rats showed less sign-tracking and more goal-tracking compared to saline controls.

CONCLUSIONS

Contrary to predictions, prior amphetamine exposure decreased sign-tracking and increased goal-tracking behavior. However, these results do support the hypothesis that psychostimulant exposure and incentive sensitization enhance behavior directed toward reward-proximal cues at the expense of reward-distal cues.

Goal- and signal-directed incentive: conditioned approach, seeking, and consumption established with unsweetened alcohol in rats

RATIONALE

Many theories of addictive behavior propose that cues signaling drug administration influence the likelihood of drug-taking and drug-seeking behavior.

OBJECTIVES

We investigated the behavioral impact of cues associated with unsweetened ethanol and their interaction with responding maintained by ethanol self-administration. Our goal was to establish the influence of such cues on ethanol seeking.

MATERIALS AND METHODS

The experiment used a matching contingency and saccharin-fading procedure to establish equal levels of responding to two spatially distinct levers using unsweetened 10% ethanol solution. After ethanol self-administration was established, a brief cue light located alternately over each lever location was either paired or unpaired (control) with the opportunity to consume the same ethanol solution. Finally, self-administration was re-established, and the effect of the cue was measured in a transfer design.

RESULTS

The reaction to lights paired with the opportunity to ingest unsweetened ethanol had three main effects: (1) induction of operant behavior reinforced by ethanol, (2) stimulation of ethanol-seeking behavior (drinker entries), and (3) cue-directed approach and contact behavior (i.e. autoshaping or sign-tracking). Cue-directed behavior to the light interacted with choice behavior in a manner predicted by the location of the cue light, enhancing responding only when the approach response did not interfere with the operant response.

CONCLUSIONS

These findings replicate and extend the effects of Pavlovian conditioning on ethanol-seeking and support-conditioned incentive theories of addictive behavior. Signals for ethanol influence spatial choice behavior and may be relevant to attentional bias shown to alcohol-associated stimuli in humans.

Relations Between Pavlovian-Instrumental Transfer and Reinforcer Devaluation

Relations between posttraining reinforcer devaluation and Pavlovian-instrumental transfer were examined in 2 experiments. When a single reinforcer was used, extended training of the instrumental response increased transfer but reduced devaluation effects. When multiple instrumental reinforcers were used, both reinforcer-specific transfer and devaluation effects were less influenced by the amount of instrumental training. Finally, although reinforcer devaluation decreased both Pavlovian conditioned responses and baseline instrumental responding, it had no effect on either single-reinforcer or reinforcer-specific transfer. These results indicate that transfer and reinforcer devaluation can reflect different aspects of associative learning and that the nature of associative learning can be influenced by parameters such as the amount of training and the use of multiple reinforcers.

Pavlovian Conditioning With Ethanol: Sign-Tracking (Autoshaping), Conditioned Incentive, and Ethanol Self-Administration

BACKGROUND

Conditioned incentive theories of addictive behavior propose that cues signaling a drug's reinforcing effects activate a central motivational state. Incentive motivation enhances drug-taking and drug-seeking behavior. We investigated the behavioral response to cues associated with ethanol and their interaction with operant self-administration of ethanol.

METHODS

In two experiments, rats received operant training to press a lever for a sweetened ethanol solution. After operant training, the animals were given Pavlovian pairings of a brief and localized cue light with the sweetened ethanol solution (no lever present). Lever pressing for ethanol was then re-established, and the behavioral effects of the cue light were tested during an ethanol self-administration session.

RESULTS

The conditioned responses resulting from pairing cue lights with the opportunity to ingest ethanol had three main effects: (1) induction of operant behavior reinforced by ethanol, (2) stimulation of ethanol-seeking behavior (magazine entries), and (3) signal-directed behavior (i.e., autoshaping, or sign-tracking). Signal-directed behavior interacted with the other two effects in a manner predicted by the location of the cue light. These conditioned responses interact with operant responding for ethanol reinforcement.

CONCLUSIONS

These findings demonstrate the importance of Pavlovian conditioning effects on ethanol self-administration and are consistent with conditioned incentive theories of addictive behavior.

Double dissociation of the effects of lesions of basolateral and central amygdala on conditioned stimulus-potentiated feeding and Pavlovian-instrumental transfer

Pavlovian conditioned stimuli (CSs) for food can enhance both the performance of instrumental responses that earn food (Pavlovian-instrumental transfer; PIT) and the consumption of food itself (CS-potentiated feeding). After a single phase of Pavlovian training, each rat was tested in both PIT and potentiated feeding tasks. Rats with lesions of the central nucleus of the amygdala failed to exhibit PIT but showed normal CS-potentiated feeding. By contrast, rats with lesions of the basolateral amygdala showed normal PIT but failed to display CS-potentiated feeding. Performances in a variety of comparison conditions suggested that both lesion effects reflected impairment of acquired motivational functions, rather than with attentional processes or the display of specific learned responses. Implications of the double dissociation of these two aspects of Pavlovian conditioned incentive motivation for amygdala function in associative learning are considered.

The effects of lateral, medial, or complete septal lesions on positive conditioned suppression in rats

This study investigated the effects of lateral, medial, or complete septal lesions in rats on lever pressing and US-approach behaviors during the presentation of a light followed by two free food pellets. Ten days after surgery, groups of rats received 20 sessions of a random interval (RI) 60-s schedule of food reinforcement. The positive conditioned suppression paradigm consisted of 20 sessions of a 10-s light paired with free food while the rats were responding on the RI 60-s schedule. All groups of rats significantly suppressed lever pressing during the 10-s light presentation. During the last four sessions of the 10-s light condition, rats with lateral septal lesions had a significant increase in food-tray entries during the light presentation, while the other groups decreased lever pressing without a change in food-tray entries during the 10-s light presentation. Although rats with septal damage generally have difficulty inhibiting responses in a variety of operant situations, rats with lateral, medial, or complete septal lesions showed no impairment in positive conditioned suppression. This study also suggests that when the spatial arrangement of the CS and the type of US were manipulated to minimize sign-tracking and goal-tracking behaviors, emotional reactions during the presentation of the CS must be considered a factor influencing positive conditioned suppression.

Enhancement of pavlovian conditioned suppression by mild ethanol intoxication

Rats were trained to bar-press for food and then received aversive Pavlovian conditioning following low doses of ethanol (0-1600 mg/kg in different groups). They were tested for Pavlovian conditioned suppression of bar-pressing 48 h, 7 days, and 14 days later following no additional differential treatments. The results showed that very low doses of ethanol (approximately 200 mg/kg) during training enhanced later conditioned suppression, whereas more moderate doses (800-1600 mg/kg) disrupted Pavlovian conditioning. These results parallel earlier observations that very low ethanol doses enhance Pavlovian conditioned eyeblink and heart rate responses in rabbits, and suggest that facilitation of Pavlovian conditioning may be a general effect of mild ethanol intoxication.

The role of observing and attention in establishing stimulus control

Early theorists (Skinner, Spence) interpreted discrimination learning in terms of the strengthening of the response to one stimulus and its weakening to the other. But this analysis does not account for the increasing independence of the two performances as training continues or for increases in control by dimensions of a stimulus other than the one used in training. Correlation of stimuli with different densities of reinforcement produces an increase in the behavior necessary to observe them, and greater observing of and attending to the relevant stimuli may account for the increase in control by these stimuli. The observing analysis also encompasses errorless training, and the selective nature of observing explains the feature-positive effect and the relatively shallow gradients of generalization generated by negative discriminative stimuli. The effectiveness of the observing analysis in handling these special cases adds to the converging lines of evidence supporting its integrative power and thus its validity.

Conditional acceleration and external disinhibition of operant lever pressing by prereward, neutral, and reinforcing stimuli

Rats responding under a differential-reinforcement-of-low-rate schedule increased their rates of lever pressing during a 20-second click/flash stimulus that preceded the delivery of a response-independent food pellet. The increase could not be attributed to suppression of collateral behavior that has been said to mediate temporally-spaced responding. We propose that the prereward stimulus functioned as an external disinhibitor of lever pressing that had been inhibited by the constraints of the operant schedule. Support is derived from the observed disinhibitory effects of a 10-second unpaired click/flash stimulus and of unsignaled, response-independent pellets that were presented while the animals were responding under the same schedule.

Appetitive Pavlovian-instrumental interactions: effects of inter-stimulus interval and baseline reinforcement conditions

Experiment I manipulated two variables which appear to influence whether a signal for food enhances or suppresses food-rewarded instrumental performance: interstimulus interval (ISI) during classical conditioning and instrumental reinforcement schedule during testing. In two groups a 10-s conditioned stimulus (CS) and food were paired (10-s and 20- to 100-s ISI), while in a third group they were unpaired. During signalled reinforcement of lever-pressing (S+), the CS suppressed responding in both paired groups. During signalled extinction (S−), responding in the 10-s ISI group was suppressed during the CS and enhanced for 60 s after CS offset; responding in the 20- to 100-s ISI group was enhanced both during the CS and for 120 s after CS offset. Experiment II examined whether the long ISI enhancement effect would occur when the baseline response rate was lowered by satiation rather than extinction. A 20- to 100-s CS and food were paired in one group and unpaired in another. After near-satiation on a CRF schedule, CS presentations caused a reduction in responding in both groups, with no significant difference between the two groups. The results of the two experiments were interpreted in terms of an interaction between the expectancy of food generated by stimuli conditioned at short and long ISIs and the expectancy of food availability controlled by the instrumental schedule.