The effect of context change upon long-term memory of CS duration

The effects of extinction-aroused attention on context conditioning

Two experiments assessed the effects of extinguishing a conditioned cue on subsequent context conditioning. Each experiment used a different video-game method where sensors predicted attacking spaceships and participants responded to the sensor in a way that prepared them for the upcoming attack. In Experiment 1 extinction of a cue which signaled a spaceship-attack outcome facilitated subsequent learning when the attack occurred unsignaled. In Experiment 2 extinction of a cue facilitated subsequent learning, regardless of whether the spaceship outcome was the same or different as used in the earlier training. In neither experiment did the extinction context become inhibitory. Results are discussed in terms of current associative theories of attention and conditioning.

Blockade of CB1 receptors prevents retention of extinction but does not increase low preincubated conditioned fear in the fear incubation procedure

We recently developed a procedure to study fear incubation, in which rats given 100 tone-shock pairings over 10 days show low fear 2 days after conditioned fear training and high fear after 30 days. Notably, fear 2 days after 10 sessions of fear conditioning is lower than fear seen 2 days after a single session of fear conditioning, suggesting that fear is suppressed. Here, we investigate the potential role of CB1 receptor activation by endocannabinoids in this fear suppression. We subjected rats to 10 days of fear conditioning and then administered systemic injections of the CB1 receptor antagonist SR141716 before a conditioned fear test was conducted 2 days later under extinction conditions. A second test was conducted without any injections on the following day (3 days after training) to examine retention of fear extinction. SR141716 injections did not increase fear expression 2 days after extended fear conditioning or affect within-session extinction; however, it impaired retention of between-session fear extinction in the day 3 test. These data suggest that CB1 receptor activation does not suppress fear soon after extended fear conditioning in the fear incubation task. The data also add to the existing literature on the role of CB1 receptors in extinction of conditioned fear.

Incubation of fear

While fear and anxiety can grow over time in anxiety disorders, most efforts to model this phenomenon with fear conditioning in rodents cause fear that remains stable or decreases across weeks or months. Here, we describe several methods to induce conditioned fear that grows over the course of 1 month and is sustained for at least 2 months using an extended fear conditioning approach. These methods include a very reliable standard method that causes multiple fear measures to increase over months, as well as alternative methods.

Cerebellar structure and function in male Wistar-Kyoto hyperactive rats

Previous research has suggested that the Wistar-Kyoto Hyperactive (WKHA) rat strain may model some of the behavioral features associated with attention-deficit/hyperactivity disorder (ADHD). We have shown that, in cerebellar-dependent eyeblink conditioning, male WKHAs emit eyeblink CRs with shortened onset latencies. To further characterize the shortened CR onset latencies seen in male WKHA rats, we examined 750-ms delay conditioning with either a tone conditional stimulus (CS) or a light CS, we extended acquisition training, and we included Wistar rats as an additional, outbred control strain. Our results indicated that WKHAs learned more quickly and showed a shortened CR onset latency to a tone CS compared to both Wistar-Kyoto Hypertensive (WKHT) and Wistars. WKHAs and Wistars show a lengthening of CR onset latency over conditioning with a tone CS and an increasing confinement of CRs to the later part of the tone CS (inhibition of delay). WKHAs learned more quickly to a light CS only in comparison to WKHTs, and showed a shortened CR onset latency only in comparison to Wistars. Wistars showed an increasing confinement of CRs to the late part of the light CS over conditioning. We used unbiased stereology to estimate the number of Purkinje and granule cells in the cerebellar cortex of the three strains. Our results indicated that WKHAs have more granule cells than Wistars and WKHTs and more Purkinje cells than Wistars. Results are discussed in terms of CS processing and cerebellar cortical contributions to EBC.

The temporal pattern of responding in conditioned bar-press suppression: the role of the context switch and training mode

The present study examined the temporal pattern of responding in a conditioned bar-press suppression task in rats. Rats were exposed to either a 30-s or a 120-s conditioned stimulus (CS) followed by a footshock. Training took place either while the rats were lever-pressing for water (online), or with the lever removed from the box (offline). They were then exposed to the CS while they were lever-pressing for water, either in the training context or in a different context. Bar-press suppression during the CS was constant across the duration of the CS during training, but was restricted to the initial portion of the CS at the time of testing, especially when subjects were tested in a different context. Those results replicate the reactive (as opposed to anticipatory) pattern observed in a lick suppression procedure by Jozefowiez et al. (2011) and indicate that a change in context at the time of testing might be critical for its expression.

Long-lasting incubation of conditioned fear in rats

BACKGROUND

In 1937, Diven reported that human fear responses to cues previously paired with shock progressively increase or incubate over 24 hours. Since then, fear incubation has been demonstrated in both humans and nonhumans. However, the difficulty of demonstrating long-lasting fear incubation in rodents has hampered the study of the underlying mechanisms of this incubation. Here, we describe a rat procedure where fear reliably incubates over time.

METHODS

We trained food-restricted rats to lever-press for food pellets in daily 90-min sessions. We then gave each rat 100 30-sec tones co-terminating with a .5-sec .5-mA footshock over 10 days (10 pairings/day). Groups of rats (n = 10-15) were then given four presentations of the tone (the fear cue) 2, 15, 31, or 61 days after fear conditioning training and were assessed for conditioned suppression of lever-pressing.

RESULTS

We found that conditioned fear responses were significantly higher 31 and 61 days after fear training than after 2 or 15 days. In control experiments, we showed that extensive tone-shock pairing is necessary for the emergence of fear incubation and that it is unlikely that non-associative factors contribute to this incubation.

CONCLUSIONS

We describe a procedure for generating reliable and long-lasting conditioned fear incubation. Our procedure can be used to study mechanisms of fear incubation and might provide a model for studying the mechanisms of delayed-onset posttraumatic stress disorder that occur in a sub-population of people previously exposed to chronic stressors.

Contextual control of inhibition with reinforcement: adaptation and timing mechanisms

Four experiments with rats studied the effects of switching the context after Pavlovian conditioning. In three conditioned suppression experiments, a large number of conditioning trials created "inhibition with reinforcement" (IWR), in which fear of the conditional stimulus (CS) reached a maximum and then declined despite continued CS-unconditional stimulus pairings. When IWR occurred, a context switch augmented fear of the CS; IWR and augmentation were highly correlated. Neither IWR nor augmentation resulted from inhibition of delay (IOD): In conditioned suppression, IWR and augmentation occurred without IOD (Experiment 3), and in appetitive conditioning (Experiment 4), IOD occurred without IWR or augmentation. IWR may occur in conditioned suppression because the animal adapts to fear of the CS in a context-specific manner. The authors discuss several implications.

Acquisition, extinction and temporal discrimination in human conditioned avoidance

Two experiments were conducted with the aim of designing a videogame for the study of human conditioned avoidance. Participants had to destroy enemy spaceships with the goal of increasing the score in a counter. Coloured signals might announce the launching of a bomb that could hit participant's spaceship producing a 30 points decrease in participant's score. Three groups of participants were trained in discriminating between a warning signal (W) and a safety signal (S) in Experiment 1. Instrumental group could avoid the loss of points by hiding the spaceship before the offset of W. Participants in the Yoked group received the same treatment received by their instrumental partners, regardless of their behaviour. In the Pavlovian group, W was always followed by the loss of points, regardless of participant's behaviour. Discrimination between W and S was better in the Instrumental groups than in the Yoked and Pavlovian control groups. Experiment 2 found extinction of avoidance when the warning signal was not followed by the bomb. Temporal discrimination was found within the participants that received the instrumental contingency in both experiments, with higher avoidance response towards the end of the warning signal. Temporal discrimination disappeared after extinction in Experiment 2.

Context and behavioral processes in extinction

This article provides a selective review and integration of the behavioral literature on Pavlovian extinction. The first part reviews evidence that extinction does not destroy the original learning, but instead generates new learning that is especially context-dependent. The second part examines insights provided by research on several related behavioral phenomena (the interference paradigms, conditioned inhibition, and inhibition despite reinforcement). The final part examines four potential causes of extinction: the discrimination of a new reinforcement rate, generalization decrement, response inhibition, and violation of a reinforcer expectation. The data are consistent with behavioral models that emphasize the role of generalization decrement and expectation violation, but would be more so if those models were expanded to better accommodate the finding that extinction involves a context-modulated form of inhibitory learning.