Conditioned Barpress Suppression Research Articles

A modified counterconditioning procedure prevents the renewal of conditioned fear in rats

Two studies using an ABA design examined the Extinction and renewal of conditioned barpress suppression. Following lights-off and foot shock pairings in Context A, rats were placed in Context B and were given either a standard counterconditioning procedure where the lights-off CS was paired with a novel food US delivered freely or a modified counterconditioning procedure where CS-US pairings only occurred if the rat earned the US by performing a required behavior during the CS. Results indicated that the modified counterconditioning procedure thwarted ABA renewal but the conventional counterconditioning procedure did not reduce ABA renewal any more than nonreinforced exposure to the CS alone. Furthermore, the response required during the modified counterconditioning procedure could be one used as a baseline response during Acquisition of fear or it could be a novel response. Implications of the results for theories of Extinction and renewal of fear are discussed.

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.

Reduced blocking as a result of increasing the number of blocking cues

Weak behavioral control (blocking) occurs when a target stimulus (X) is paired with an outcome in the presence of a well-established signal for the outcome (i.e., a blocking stimulus). Conventional Pavlovian conditioning theories explain this effect by asserting that a discrepancy between expected and experienced outcomes is necessary for learning about X and that no such discrepancy exists in blocking situations. These theories anticipate that the effect of additional well-established signals for the unconditioned stimulus (US) should be additive. In two conditioned barpress suppression experiments using rats as subjects, the opposite result was observed. Experiment 1 provided evidence that blocking was reduced when two blocking stimuli were present during X-US pairings relative to when one blocking stimulus was present. Experiment 2 elaborated on the mechanisms underlying the observations in Experiment 1, while explaining the discrepancy between the results of Experiment 1 and prior reports of the additivity of blocking stimuli.

Primacy effects induced by temporal or physical context shifts are attenuated by a preshift test trial

When subjects are sequentially trained with a cue (A) paired separately with two outcomes (B and C) in different phases (i.e., A-B pairings followed by A-C pairings) testing in the training context after short retention intervals often reveals recency effects (i.e., stronger influence by A-C). In contrast, testing after long retention intervals or testing in a context different from that of training sometimes reveals primacy effects (A-B). Three experiments were conducted using rats in a Pavlovian conditioned bar-press suppression preparation to ascertain whether a nonreinforced test trial in the training context soon after training can attenuate this shift to primacy. Experiment 1 demonstrated that exposure to A shortly after both phases of training, but prior to a long retention interval, can attenuate shifts from recency to primacy otherwise observed with a long retention interval. Experiment 2 showed that exposure to A in the training context can also eliminate the shift from recency to primacy otherwise produced by shifting the physical context between training and test. Experiment 3 discredited a potential account of the results of Experiments 1 and 2. The effects observed in Experiment 1 and 2 are interpreted as early testing in the training context serving to initiate rehearsal of the A-C association due to the temporal proximity of A-C training.

Contrasting reduced overshadowing and blocking.

Preexposure of a cue without an outcome (X-) prior to compound pairings with the outcome (XZ-->O) can reduce overshadowing of a target cue (Z). Moreover, pairing a cue with an outcome (X-->O) before compound training can enhance its ability to compete with another cue (i.e., blocking). Four experiments were conducted in a conditioned bar-press suppression preparation with rats to determine whether spacing of the X- or X-->O trials would differentially affect reduced overshadowing and blocking. Experiment 1a showed that reduced overshadowing was larger with massed trials than with spaced trials. Experiment 1b found that blocking was larger with spaced trials than with massed trials. Experiments 2a and 2b indicated that these effects of trial spacing were both mediated by the associative status of the context at test. The results are interpreted in the framework of contemporary learning theories.

Interaction of retention interval with CS-preexposure and extinction treatments: Symmetry with respect to primacy

Imposition of a retention interval between cue-outcome pairings and testing can alleviate the retardation of conditioned responding induced by pretraining exposure to the cue (i.e., the CS-preexposure effect). However, recent studies have reported an enhanced effect of CS-preexposure treatment with longer retention intervals (De la Casa & Lubow, 2000, 2002; Lubow & De la Casa, 2002). In a series of conditioned barpress suppression studies with rats, we examined the effects of imposing a retention interval just prior to testing following either CS-preexposure (cue alone before cue-outcome pairings) or extinction (cue alone after cue-outcome pairings) treatments. Experiment 1 replicated in a different preparation recent reports of CS-preexposure treatment effects increasing with longer retention intervals. Experiment 2 showed that spontaneous recovery of stimulus control of behavior after extinction can be obtained with the same parameters as those used to observe the augmented effect of CS-preexposure treatment. In Experiment 3, both the augmented effect of CS-preexposure treatment and spontaneous recovery from extinction were found when we used, in place of a retention interval, an associative priming manipulation.

Unblocking with Qualitative Change of Unconditioned Stimulus

Conditioned barpress suppression was used to examine the effects of qualitative changes in the unconditioned stimulus (US) between Phases 1 and 2 of a blocking paradigm. In Phase 1, rats received pairings of a conditioned stimulus (CS) with footshock. In Phase 2, experimental subjects received a single trial of the same CS or a different CS compounded with a second stimulus and followed either by a footshock or an ice water dunking. These two USs were equated in their potential to elicit conditioned suppression of barpressing. Less blocking of the second stimulus (i.e., unblocking) was observed in subjects that received a qualitative change in US between phases than in subjects for which the US was consistent between phases. This unblocking effect is discussed with respect to the differences between various models of conditioning and several prior successes and failures to demonstrate unblocking.

Blocking but Not Conditioned Inhibition Results When an Added Stimulus Is Reinforced in Compound with Multiple Pretrained Stimuli

Conditioned barpress suppression by rats was used to explore the associative status of an initially neutral stimulus that was reinforced in simultaneous compound with two independently pretrained conditioned excitors. In contrast to the Rescorla-Wagner model, which predicts that the target stimulus (X) will be inhibitory following such A+/B+/ABX+ training, the present study found no evidence that X acquired inhibitory associative strength. Rather, the pretrained stimuli merely served to block conditioned excitatory responding to the target stimulus.

Suppression of operant vs consummatory behavior.

The magnitude and variability of conditioned suppression of bar pressing and dipper licking were compared. In two steady-state experiments, suppression of bar pressing was more profound and more stable from day to day. The two measures of suppression were uncorrelated as indexed by Pearson product-moment correlation coefficients computed for adjacent trials. Correlations within measures (internal consistency) were somewhat higher for the bar-press system except when a high proportion of rats completely suppressed on one of the correlated trials. In a transient state experiment in which possible adventitious punishment of both response systems was eliminated, suppression of bar pressing was again more profound and considerably slower to extinguish.

The truly random control as an extinction procedure

CS-alone trials or random presentations of CSs and USs were interpolated between Pavlovian defense conditioning and later measurement of the Pavlovian CR (conditioned suppression of barpressing). Although both procedures equally degraded the CS-US contingency, only the CS-alone procedure significantly weakened the previously established CR.

Role of the olfactory bulbs in the detection of ionizing radiation by the rat

The sensitivity to X-rays in the albino rat was studied following destruction of the olfactory bulbs. The two procedures of conditioning an aversion to saccharin solution with X-rays as the unconditioned stimulus and conditioned bar press suppression with X-rays as the warning stimulus were both used in testing the sensitivity to the ionizing radiation. The profound aversion to saccharin flavored water, obtained in rats after a single pairing of X-rays with the saccharin solution, was found to be diminished in animals which had olfactory ablations. The conditioning of sham operated animals and those with frontal lesions resulted in the usual significant saccharin aversion. The immediate detection of X-rays was profoundly affected by removal of the olfactory bulbs. Animals which had previously been conditioned to suppress a bar-pressing response in the presence of X-rays failed to show this suppression after complete removal of the olfactory bulbs. When ablation was incomplete, with removal of tissue from the frontal lobes, or with sham operations, the animals continued to show the suppression effect at the onset of X-ray exposure.