Strain differences in avoidance conditioning as a function of the classical CS-US contingency.

Examined rates of shuttle box avoidance responding in 3 strains of rats as a function of classical and instrumental contingencies in 2 experiments. Ss were a total of 126 female albino Fischer, Lewis, and Long-Evans rats. In Exp I, during classical conditioned-stimulus-unconditioned-stimulus (CS-UCS) pairings in the absence of an avoidance contingency, there were large differences between the 3 strains in rates of anticipatory responding to the CS. The same pattern of differences was observed in Exp II when the avoidance contingency was added. None of the instrumental contingencies of CS termination, UCS termination, or the avoidance contingency differentially affected the strains. Classically elicited anticipatory responses and their compatibility with the required avoidance response were viewed as central factors in both the acquisition and maintenance of skeletal avoidance responses. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of pretraining compatible and incompatible responses on subsequent one-way and shuttle-avoidance performance in rats.

Conducted 6 experiments with male Holtzman rats. A single noncontingent footshock was found to facilitate subsequent one-way and shuttle avoidance if the CS in preshock and avoidance training was the same. If the to-be-established instrumental response was punished during preshock, or if Ss were required to run toward the CS paired with shock during pretraining, the facilitative effects of preshock were eliminated. Facilitation by a single preshock was not enhanced if shock was escapable, regardless of the CSs, task, or whether escape was immediate or delayed. If Ss received 10 one-way escape trials, the beneficial effects of preshock on one-way and shuttle avoidance were enhanced. In contrast, shuttle-escape training produced no such beneficial effects on avoidance performance. (19 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of unconditioned stimulus escape and avoidance in discriminative avoidance learning in the gerbil (Meriones unguiculatus).

Gave separate groups of male gerbils (N = 80) shuttle-avoidance training or classical trials (CS and UCS pairings) in a 100-trial session. The shock UCS was either escapable or inescapable (i.e., of fixed duration-.1-3.0 sec). CRs, intertrial interval responses, and observations of the Ss' reactions to each UCS were recorded. Avoidance learning emerged only in groups exposed to escapable shock or a brief inescapable shock. Based on both the observational data of the nature of the shock-elicited reactions and shuttle performance, it is concluded that response termination of the UCS is not necessary for shuttle-avoidance learning. Results are discussed in terms of a punishment theory of avoidance and the species-specific defense-reaction hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of exposure to conditioned stimulus and control of its termination in the extinction of avoidance behavior.

Describes 2 experiments in which, following signaled shuttle box avoidance training, a total of 52 female Fischer344 rats were exposed to the conditioned stimulus (CS) during no-shock treatment trials and subsequently tested during extinction trials in which shock was also absent. In Exp I, Ss that could control the termination of the CS during treatment responded significantly more often during extinction than yoked partners that received the same pattern and duration of CS exposure but could not control its termination. Exp II revealed that the probability of responding during extinction was a decreasing function of the duration of CS exposure during treatment. Thus, in the absence of shock, both lack of control over CS termination and increasing CS exposure each independently facilitated the weakening of well-established avoidance responses. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

DSP4 (N-2-chloroethyl-N-ethyl-2-bromobenzylamine), a new noradrenaline neurotoxin, and stimulus conditions affecting acquisition of two-way active avoidance.

Several CS and UCS variables known to affect the rate of acquisition of the 2-way active avoidance task were investigated in rats treated with the novel selective noradrenaline neurotoxin DSP4 (50 mg/kg, ip). 234 male Sprague-Dawley rats were used in 6 experiments. Although the DSP4 Ss did not demonstrate the linear relation between CS duration and avoidance acquisition to the same extent as controls, their avoidance performance was as drastically disrupted as that of the controls both by preexposure to the CS and by increasing levels of shock intensity. DSP4 Ss also evidenced fear retention for the shuttle box cues previously associated with inescapable shocks to as marked a degree as control Ss. Biochemical data indicated profound noradrenaline depletion in the cortex and hippocampus and a lesser depletion in the hypothalamus. Findings offer a behavioral characterization of the consistent DSP4-induced impairment of 2-way active avoidance acquisition. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Slow reacquisition following extinction: Context, encoding, and retrieval mechanisms.

Investigated the slow reacquisition (RAQ) of responding in rats that occurs when the conditioned stimulus/stimuli (CS) and unconditioned stimulus/stimuli (UCS) are paired again after prolonged extinction training. In Exp 1, an extinguished CS acquired less suppression than a novel CS during a final conditioning phase, but more suppression than CSs that had received comparable nonreinforcement without initial conditioning. In Exp 2, CS–UCS pairings resumed in the context of extinction caused the least RAQ of suppression: Pairings in a neutral context produced better RAQ, while return of the CS to the conditioning context caused an immediate renewal of responding to the CS. In Exp 3, a return of the CS to the extinction context after RAQ training caused renewed extinction performance and interfered with performance appropriate to RAQ. This effect was not due to demonstrable inhibitory conditioning of the extinction context. Results suggest that representations of conditioning and extinction (or CS–UCS and CS–no UCS relations) are both retained through extinction and that performance appropriate to either phase can be cued by the corresponding context. RAQ may thus be slow when the context retrieves an extinction memory. Similar mechanisms may also play a role in other Pavlovian interference paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation and nonfacilitation of active avoidance behavior of rats with septal lesions in the shuttle box and running wheel.

Hypothesized that facilitation of avoidance performance of rats with septal lesions occurs only in tasks that punish responses having the same topography as the avoidance response, such as intertrial responses, or tasks that have aversive consequences for making the avoidance response, such as a brightly illuminated safe compartment. 28 male Sprague-Dawley rats (Exp I) were trained in 2 shuttle box tasks, and 24 (Exp II) were trained in 2 running-wheel avoidance tasks under conditions of punishment or nonpunishment of intertrial responses. Ss with septal lesions performed better than controls in both the shuttle box and the wheel tasks when intertrial responses were punished. When intertrial responding was not punished, experimental and control groups did not differ in avoidance performance. Avoidance performances of punished and unpunished Ss with septal lesions did not differ from each other or from unpunished controls in either wheel or shuttle box tasks. Results are discussed in the context of the species-specific defense reaction (SSDR) avoidance theory of R. C. Bolles (see record 1970-04813-001). It is suggested that septal lesions interfere with the suppression of ineffective SSDRs. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of an aversive Pavlovian conditional stimulus with aversively and appetitively motivated operants in rats.

Reports results of 5 experiments with a total of 168 male albino Sprague-Dawley rats. Presentation of an aversive CS produced an acceleration of free-operant Sidman shock-avoidance responding only if the CS had been paried with a relatively weak-shock UCS. Stimuli paired with a relatively strong UCS produced suppression of avoidance responding. With appropriate shock intensities, both suppression and acceleration were obtained. Responses of controls showed that this effect was not due to interactions between the operant response and UCS. In a within-S experiment, the same aversive CS produced suppression of an appetitive response (CER) and acceleration of avoidance. However, a CS which had produced avoidance acceleration did not suppress an appetitive operant. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of response restriction during exposure to inescapable shock upon subsequent one-way and shuttle-avoidance performance in rats.

Investigated the effects of signaled inescapable shock on subsequent avoidance performance in 3 experiments with male Holtzman rats (N = 188). Exp I indicated that prior shock exposure (PSE) facilitated 1-way and shuttle avoidance. When Ss were preshocked in a harness so that free mobility was not possible, the facilitative effects of PSE on shuttle, but not 1-way avoidance performance, were largely reduced. Exp II indicated that activity during CS periods following PSE was greater among unrestrained than restrained Ss. Exp III showed that immobilization via injection of succinylcholine chloride did not affect the facilitative effects of PSE relative to that of Ss preshocked in a harness. Results are interpreted in terms of response repertoire changes produced by PSE in conjunction with the response requirement of the avoidance task. (French summary) (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reinforcement versus species-specific defense reactions as determinants of avoidance barpressing.

In three experiments, rats whose escape and avoidance barpresses were reinforced by entering a safe floor in an otherwise shuttle conditioning arrangement (a shuttle barpress task) showed better learning than the rats that did not receive such reinforcement only when the shock intensity was very weak. Barpresses were found to have mostly nonfrontal topography and appeared not to be under the control of escape or avoidance contingency of reinforcement. Preavoidance training in which only frontal barpresses were allowed to terminate shock greatly facilitated avoidance responding and nullified the inverse effect of shock intensity. The findings were interpreted as indicating that innate defensive reactions play a more prominent role in avoidance behavior than reinforcement, but they do not appear to be as fixed and unmodifiable by learning as often suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences in strains of rats during extinction of shuttle box avoidance responding.

In 2 experiments differences between strains of rats in the extinction of shuttle box avoidance responding were examined as a function of the classical conditioned stimulus-unconditioned stimulus (CS-UCS) and instrumental CS termination contingencies. Ss were a total of 68 female albino Fischer, Lewis, and Long-Evans rats. When classical CS-UCS pairings were given on all trials, responding declined somewhat. When this contingency was altered by omitting shock entirely or preventing the pairing of CS and shock, behavior weakened even further. Whereas responding was indistinguishable under both prompt and delayed CS termination during the paired-shock procedure, it was generally higher under prompt CS termination during the no-shock and unpaired-shock procedures. However, the strains differed widely during extinction, with Fischer rats responding more often during the paired and unpaired procedures and Long-Evans rats more often in the no-shock procedure. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failure to learn to escape by rats previously exposed to inescapable shock is partly produced by associative interference.

2 experiments demonstrated that the effects of prior exposure to inescapable shock on the subsequent acquisition of an escape response in rats is determined by the nature of the contingency that exists between responding and shock termination during the escape learning task, and not by the amount of effort required to make the response or the amount of shock that the S is forced to receive during each trial. Exp I, using 48 male Simonsen rats, showed that inescapably shocked Ss did not learn to escape shock in a shuttle box if 2 crossings of the shuttle box were required (fixed ratio, FR, -2) to terminate shock, but did learn this FR-2 response if a brief interruption of shock occurs after the 1st crossing of the FR-2. Exp II with 72 Ss showed that inescapably shocked Ss learned a single-crossing escape response as rapidly as did controls, but were severely retarded if a brief delay in shock termination was arranged to follow the response. Results are discussed in terms of the learned helplessness hypothesis, which assumes that prior exposure to inescapable shock results in associative interference. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Escape from fear: A detailed behavioral analysis of two atypical responses reinforced by CS termination.

Escape from fear (EFF) is a controversial paradigm according to which animals learn to actively escape a fear-eliciting conditioned stimulus (CS) if the escape response (Re) is paired with CS termination. Some theories posit that EFF learning is responsible for instrumental avoidance conditioning. However, EFF learning has typically been weaker than avoidance learning and difficult to reproduce. The authors examined EFF learning and memory with 2 atypical Res: rearing and nose-poking. The data suggest that rearing, but not nose-poking, can be learned as an instrumental EFF response. Further, EFF memory was response specific, aversively motivated, and controlled by the CS. Successful EFF learning also resulted in better long-term elimination of a passive fear reaction (freezing). Factors important for EFF experiments and theoretical considerations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of amygdala central nucleus lesions on blocking and unblocking.

The effects of lesions of the amygdala central nucleus (CN) on blocking and unblocking of appetitive Pavlovian conditioning were examined in 2 experiments with rats. In both lesioned and unlesioned rats, prior pairing of one CS with a food unconditioned stimulus/stimuli (UCS) blocked the acquisition of conditioning to a 2nd CS when a compound of both stimuli was paired with that same UCS. If the value of the UCS was increased or decreased when the 2nd CS was added, unlesioned rats acquired substantial conditioning to the 2nd cue (unblocking). Unblocking occurred in lesioned rats only when the UCS value was increased. In both lesioned and unlesioned rats, unblocking was prevented if the compound cue was paired with the original UCS prior to the change in UCS value. These data suggest that the CN is involved in increasing attention to signals for significant events but not in tuning out redundant cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of US devaluation on win–stay and win–shift radial maze performance in rats.

Previous studies have shown double dissociations between win–stay and win–shift radial maze learning in terms of their underlying neural substrates. To examine the content of the associations formed in the two tasks, the authors devalued the food unconditioned stimulus (UCS) by taste aversion to differentiate stimulus–stimulus(CS–UCS) and stimulus–response (CS–CR) learning. UCS devaluation was performed in rats that were over- or undertrained on the win–stay task. Devaluation substantially reduced food consumption on the maze but failed to disrupt choice accuracy, regardless of the amount of training. Devaluation did not affect latency in overtrained rats but did increase latency in undertrained rats. In the win–shift task, devaluation caused rats to reject the reinforcer, yet they continued to accurately win–shift, but with significantly longer latencies (Experiment 3). The results suggest that an S–R association may mediate performance after extended win–stay training. In contrast, a UCS representation appears to be recalled during early win–stay and win–shift performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

CS modality transfer of two-way avoidance in rats with central and basolateral amygdala lesions

Post-lesion acquisition of two-way avoidance and subsequent transfer to two warning signals (conditioned stimulus, CS) of different modality were investigated in 60 rats. In Experiment I the animals were originally trained with less salient (darkness) CS, then transferred to more salient compound (darkness and white noise), and finally to white noise CS. The opposite arrangement of the conditioned stimuli (CSi) during the subsequent stages was employed in Experiment II. In control animals, avoidance acquisition was faster and the intertrial responding (ITR) rate lower with the auditory than with the visual CS. Lesioned rats learned avoidance responses more slowly, independently of CS modality. The transfer to other CSi revealed dramatic between-group difference in the level and consistency of avoidance response, shuttle-box latencies and ITR rate. In control animals, transfer to more salient CSi enhanced avoidance performance, whereas change to less salient CS decreased it. Rather small changes in shuttle-box performance and consistency of avoidance response due to CS modality were seen in rats with the basolateral lesions. In contrast, central nucleus injury caused a strong deterioration in the avoidance transfer, especially when the visual CS followed the acoustic one. The results indicate differential involvement of the basolateral and central amygdala nuclei in stimulus-processing mechanisms of instrumental defensive behavior.     

Conditioning the unconditioned response: Modification of the rabbit's (Oryctolagus cuniculus) unconditioned nictitating membrane response.

Conditioning-specific reflex modification (CRM) occurs when classical conditioning modifies responding to a unconditioned stimulus/stimuli (UCS) in the absence of a conditioned stimulus (CS). Three experiments monitored rabbit (Oryctolagus cuniculus) nictitating membrane unconditioned responses to 5 intensities and 4 durations of periorbital electrical stimulation before and after CS or UCS manipulation. CRM occurred after 12 days of CS-UCS pairings but not following unpaired CS/UCS presentations or restraint. CRM survived CS-alone and CS/UCS-unpaired extinction of the conditioned response (CR) but not presentations of the UCS alone, although CRs remained intact. Thus, CRs could be weakened without eliminating CRM and CRM could be weakened without eliminating CRs. Data indicate CRM is a reliable, associative effect that is more than a generalized CR and may not be explained by habituation, stimulus generalization, contextual conditioning, or bidirectional conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bridging temporal gaps between CS and US in autoshaping: Insertion of other stimuli before, during, and after CS.

In 4 experiments, female White Carneaux pigeons were exposed to key-light illuminations separated from food delivery by 12–60 sec. Approach to the key light did not develop on conventional trace-conditioning arrangements but occurred consistently whenever some auditory or visual stimulus filled the CS–UCS gap (serial conditioning) or was always present except during the gap. The CS approach was strong only when the stimulus present during the intertrial interval remained on until the termination of CS; if the stimulus ended at CS onset, conditioning did not occur. Although discriminability of CS–UCS gaps from intertrial periods seemed necessary for conditioning to occur in the absence of close CS–UCS contiguity, the outcome of the final experiment indicates that such discriminability was not sufficient for conditioning. Results are discussed in terms of possible 2nd-order conditioning effects and the changes in the associative strength of the "local context" existing when the CS appears, which may lead to superconditioning of CS. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Corticosterone is involved in foot shock-induced inactivity in rats

Inescapable shock (IS) exposure induces behavioral inactivity, related to behavioral alterations in subsequent tests (i.e., escape failure, and inactivity during shuttle box task). Metyrapone (150 mg/kg, IP), a corticosterone (CS) synthesis inhibitor, administered 3 h prior to IS reduced inactivity during this aversive experience. Forty-eight hours later, when these rats were submitted to a shuttle box task, a reduction in both escape failure and inactivity was observed. These effects were reversed by CS (20 mg/kg, SC) and dose dependent of the synthetic glucocorticoid dexamethasone, both administered 1 h before IS. When metyrapone was administered 3 h before the shuttle box task to IS-exposed animals, escape failures and inactivity were markedly reduced. This effect was subsequently reversed by CS. The dynamics of changes in serum CS concentrations after both IS and shuttle box task paralleled behavioral changes. Animals injected with metyrapone before IS, which displayed active behavior, showed serum CS levels stable at their basal levels after shock, and their secretion pattern was quite attenuated after the shuttle box task, whereas vehicle-, CS alone-, and metyrapone + CS-injected animals showed higher serum CS concentrations post-IS, which slowly decreased to their corresponding basal levels. CS secretion after the shuttle box task was similar for the three groups: it had the same magnitude as after IS, though the decrease was faster. In all groups, animals displayed passive behavior. These results indicate that glucocorticoids are involved in the onset and expression of passive behaviors induced by uncontrollable stressors. Therefore, it is possible to suggest a functional relationship between CS released by exposure to inescapable stressor and the behavioral strategies adopted by rats under this stressful condition.     

Differential control by context in the inflation and reinstatement paradigms.

Examined, in 5 conditioned suppression experiments, the influence of summation between fear of the CS and the context in experimental paradigms in which the rat is exposed to UCSs following conditioning or extinction. Context-preference tests assessed contextual fear. In Exps I–III with 88 female Wistar rats, the inflation paradigm, in which fear of a CS paired with a weak UCS is enhanced by exposure to intense UCS alone, was investigated. Results show that the contextual fear that was present when the target CS was tested was reduced by presenting the intense UCSs in a different context, by exposing Ss to the context following their presentation, and by signaling the intense UCSs with a 2nd CS. In Exp IV with 32 female Wistar rats, UCS exposures following conditioning or extinction both produced contextual fear, but only fear of the extinguished CS was reinstated by that fear. In Exp V with 32 female Wistar rats, identical amounts of contextual fear reinstated fear of an extinguished CS, but not a nonextinguished CS, when the 2 types of CSs were arranged to evoke comparable amounts of fear prior to testing. It is suggested that contextual fear plays a role in the reinstatement paradigm but not in the inflation paradigm. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)