共查询到20条相似文献，搜索用时 31 毫秒
1.
Jon L. Williams 《Learning & behavior》1987,15(3):333-341
In Experiment 1, rats received a session of 80 inescapable tail shocks or no shocks while restrained in a tube. During tests of conditioned defensive burying 24 h later, the bedding of the chamber contained odors from either stressed or nonstressed conspecific donor rats. Following a single prod shock, subjects that had had prior shocks or that were tested with the stress odors spent significantly less time burying the prod, made smaller piles of bedding, and displayed more freezing behavior. The combination of prior shock and stress odors during later testing enhanced these effects. In Experiment 2, a yoked group of rats that was given inescapable shocks, in contrast to a group that had wheel-turn escape training and one that was restrained but not shocked, later showed significantly less burying and more freezing when tested for defensive burying with stress odors present. In both experiments the duration of burying and the heights of piles were positively correlated, and both of these measures were negatively correlated with freezing. The demonstrated capacity of unconditioned stress odors to mediate different degrees of fear, depending upon the controllability of prior shock, is related to other studies of learned helplessness, and the predominance of freezing over burying is discussed in terms of various types of defensive strategies, stimulus-control processes, and the author’s stress-coping-fear-defense (SCFD) theory. 相似文献
2.
Time spent in various behaviors by the rat was recorded in a defensive burying paradigm. Experiment 1 revealed that rats spent more time burying the shock prod than a control prod and that doubling the size of the test chamber did not have a significant effect on the time spent in any behavior. In Experiment 2, the location of bedding material in a two-compartment test chamber was found to affect the occurrence of burying (both the shock and control prods) and burrowing behavior. Burying did not occur when bedding was not available in the shock compartment but was located in the escape compartment. Burrowing was more likely to occur when bedding was in both compartments than when it was in only one compartment. Immobility and escape latencies were shorter than burying latencies in all subjects. Burying was viewed as belonging to a second stage of defensive behavior. 相似文献
3.
In Experiment 1, four groups of male rats were given a session as an intruder in either aggressive (i.e., alpha) or nonaggressive colonies of conspecifics and later received either a 2-h exposure to the odors of the alpha colonies or an exposure-control session with the odors of a nonalpha colony. Two additional groups of rats that had been attacked and defeated by alpha residents were later given a 12-h exposure session with alpha-colony odors or nonaipha-control odors. Twenty-four h after the colony-intruder session, all subjects were given a single 6.5-mA shock from a prod with alpha-colony odors present in the bedding of the test chamber. Attacked rats that had been given exposure-control sessions showed significantly less prod burying and greater freezing than nondefeated subjects. This implies that the alpha-colony odors elicited conditioned fear. In contrast, the attacked subjects that had been given a pretest exposure session with alpha-colony odors showed significantly more prod burying and significantly less freezing. This suggests that the alpha-odor exposure resulted in the extinction of fear to these odors. Furthermore, the 12-h exposure to alpha-colony odors was found to be more effective in reducing fear-mediated responses than was the 2-h exposure. In Experiment 2, three groups of rats were exposed to a cat while they were in a protective cage; later they were given a 12-h exposure session with cat odors, a 12-h exposure-control session with no cat odors, or no exposure treatment. Compared with the two control groups, the subjects that were exposed to cat odors showed less freezing during subsequent prod-shock tests in the presence of cat odors, but they did not show prod burying. The reported changes in fear-mediated reactions to the odors of conspecifics and a predator are discussed in terms of both associative and nonassociative processes. 相似文献
4.
Rats shocked once by a stationary, wire-wrapped prod mounted on the wall of the test chamber incorporated sand, wooden blocks, or commercial bedding material on the floor of the chamber into a defensive response. They moved the available material toward and over the shock prod in all three conditions, adapting the response topography to the particular demands of the available material. In the sand and bedding conditions, the rats buried the prod by pushing and spraying piles of the material with snout and forepaws, whereas, in the blocks condition they picked up the blocks with their teeth and placed them individually around the prod. In Experiment 2, the rats buried the shock prod with blocks even when they had to first carry the blocks to the prod from the back of the chamber. Thus, conditioned defensive burying is not a simple, reflexive response to objects paired with a painful stimulus: it is a complex behavioral sequence that can vary as a function of the availability of burying materials. 相似文献
5.
In Experiment 1, male rats were exposed to either aggressive (i.e., alpha) or nonaggressive conspecific colonies and tested 24 h later, with or without alpha odors, for freezing behavior and burying of a wall prod that had been the source of a brief electric shock. The results indicated that prior defeat experience and the presence of alpha odors alone during testing had no significant effects, but the combination of prior defeat and alpha-odor testing significantly decreased burying and increased freezing behavior. In Experiment 2, we examined the effects of noncontact exposure to a cat, as a predatory Stressor, during subsequent prod-shock tests involving the presence or absence of cat odors. Exposure to a cat failed to disrupt later prod burying and did not produce freezing. However, the presence of cat odors during testing significantly reduced the amount of defensive burying,without resulting in an increment in freezing. In Experiment 3, rats were given 1, 5, or 30 inescapable preshocks in the presence of either cat odors or a hedonically neutral citronella odor and were tested 24 h later for prod burying and freezing with or without these odors. Both the cat and the citronella odors resulted in a significant reduction in burying and an increase in freezing for rats given 5 and 30 preshocks and tested in the presence of these respective conditioned odors. For the groups that were given 5 preshocks, preshock and later testing in the presence of cat odors resulted in significantly less prod burying and more freezing than for rats that were preshocked and tested in the presence of citronella. The findings of these three ethoexperimental studies are discussed in terms of the learned-helplessness theory, the stress-coping-fear-defense (SCFD) theory, and the concept of selective CS-US associability. 相似文献
6.
Douglas A. Williams 《Learning & behavior》1994,22(2):203-213
Extinction of rats’ conditioned defensive freezing responses in a context associated with two bouts of massed shock (3 sec) separated by a long unreinforced interbout interval was slower than that in a context associated with distributed shock (60 sec). Resistance to extinction following two bouts of massed shock depended on the rats’ remaining undisturbed in the conditioning context during the long unreinforced interbout interval. Slow extinction of freezing was attributed to either the summation of temporal conditioning at the early and late session times or the formation of an association between the early and late bouts of shock. Importantly, the effects of the two bouts of massed shock could not be explained by what is known about the reinforcing effectiveness of massed shock. 相似文献
7.
Rats shocked once by a stationary, wire-wrapped prod bury it if suitable materials are available. Does this conditioned defensive burying occur when rats have the opportunity to flee from the source of aversive stimulation, or is it limited to situations such as those in which it had previously been studied—those in which the relatively small test chamber confined each rat to the immediate vicinity of the prod? In the present experiments, the capacity of rats to flee from the shock prod was enhanced by increasing the floor dimensions of the test chamber up to 200X80 cm (Experiment 1) or by providing the rats with an opportunity to seek refuge in a separate, safe compartment (Experiment 2). Although both of these modifications to the usual conditioned-defensive-burying paradigm significantly reduced the duration of burying and the height of the accumulated mounds, burying remained well above control levels in all experimental conditions. 相似文献
8.
Natural sources of aversive stimuli are frequently well-defined material objects that are present both before and after the aversive event. In the present experiment, rats acquired information about such a source after the aversive event and used this information to guide their subsequent defensive reactions to it. The rats were shocked by one of two possible sources, either a black or a striped prod, mounted on opposite end walls of the test chamber. Immediately following the shock, the houselights were momentarily extinguished and the patterns on the two prods were automatically switched for subjects in the experimental condition or left unchanged for subjects in the control condition. The rats were left in the chamber for another 5 min with the patterns in their new positions before being removed for 2 min while the two prods were mounted on the side walls. During the ensuing test of conditioned defensive burying, the rats in the control condition directed the majority of their burying behavior at the prod exhibiting the pattern displayed by the shock source prior to and during the shock administration. In contrast, the rats in the experimental group buried the prod exhibiting the pattern displayed by the shock source during the postshock period more than they did the prod displaying the pattern present on the shock source prior to and during the shock administration. 相似文献
9.
Genotypically based within-species differences in defensive burying were examined in 180 mice representing 15 inbred strains. Each mouse was tested twice in a cylindrical test chamber containing two similar prods. In the first test, one of the prods was electrified, whereas in the second test (24 h later), neither prod was. Although most strains selectively buried the shock prod in the first test (as determined by bedding-height-at-prod and position-of-highest-bedding-pile criteria), some strains did not discriminate between the shock and dummy prods and still others displayed little prod-directed bedding displacement at all (thereby resembling a heterogeneous nonshocked control group). In general, burying tended to be somewhat reduced in the second test, but strain differences in retention were observed. Factors contributory to the observed differences among strains and the need for multiple measures of burying are discussed. Collectively, these findings indicate that intraspecific genetic variation, acting at multiple burying-relevant behavioral levels, can be an important determinant of the expression of the defensive-burying response in mice. 相似文献
10.
Heidar A. Modaresi 《Learning & behavior》1982,10(1):97-102
Experiment 1 investigated the proposition that rats cover the source of aversive stimulation with the bedding material available to them and sought to determine whether familiarization with this material would affect burying. The results indicated that rats are no more likely to cover an aversive object than they are not to cover it, although they collect a considerable amount of bedding material in the area surrounding the aversive object. Experiment 2 demonstrated that the rat’s defensive “burying” toward an aversive object is affected by the subject’s predisposition to displace material toward the front side of the apparatus. Some theoretical complexities involved in considering the act of “burying” toward an aversive object as a defensive behavior are discussed. 相似文献
11.
Two studies used a one-trial-a-day aversive conditioning procedure with rats as subjects to investigate the effects of a noise versus a light CS on conditioned freezing. Experiment 1 demonstrated that less conditioned freezing was elicited by the light, although the two CSs led to similar levels of freezing to the contextual cues of the conditioning chamber. Experiment 2 replicated these outcomes and showed that the manipulation of CS intensity produced results similar to those of modality, with the more intense CSs eliciting less freezing. The second experiment also determined that freezing to contextual cues resulted from context conditioning. According to the Rescorla-Wagner model, CSs that condition poorly should generate little competition with context conditioning. Since neither the modality nor intensity factor reliably influenced context conditioning, as measured by context-evoked freezing, the studies provide no support for the view that the effects on CS-evoked freezing represent differences in the strength of conditioning to the various stimuli. This finding raises the possibility that all of the CSs conditioned well but varied in their abilities to elicit freezing because they differed in terms of the form of defensive behavior under their control. 相似文献
12.
In two experiments, we examined the effects of a wide range of interstimulus intervals (2.5, 15, 45, 120, 135, and 405 sec) on one-trial context fear conditioning with rats. Here, the interstimulus interval (ISI) denotes the time between placement in a conditioning chamber and the onset of a single footshock. On the conditioning day, we observed that the rats’ behavior at the time of shock onset varied systematically across ISI values. On the subsequent test day, we used context-evoked freezing as a measure of context conditioning and found the well-known inverted U-shaped ISI function. We also found that conditioned freezing for the shortest ISI values was concentrated early in the test session, whereas freezing at longer ISIs was distributed more evenly throughout the test session. The freezing results found here are more consistent with the literature on conditioning with punctate cues than are previously described results from one-trial context fear-conditioning procedures. 相似文献
13.
In two experiments, we examined the conditions under which signaling an unconditioned stimulus (US) with a nominal conditioned stimulus (CS) interferes with the conditioning of situational cues in defensive freezing in the rat. Subjects received footshock USs that were (1) either signaled or unsignaled and (2) either varied or fixed in their temporal location within the conditioning session. Experiment 1, with only one trial per session, yielded no evidence that signaling affected pretrial freezing using either a fixed or variable interval between placement in the context and shock onset. In a test in which no CSs or footshocks were presented, groups that previously had received footshock at a fixed temporal location showed greatest freezing at around that same time. For groups that had received footshocks at various times, freezing declined across the test session. Experiment 2 showed overshadowing of pretrial freezing after more extensive conditioning with many trials per session, but only if the intershock intervals were variable rather than fixed. 相似文献
14.
The degree of spatial and temporal contiguity between contact with a prod and shock was varied in three experiments to see how these factors contribute to defensive burying. In Experiment 1, rats shocked once through a grid floor while touching a prod buried the prod just as much as did rats shocked through the prod. Experiment 2 showed that rats either shocked through the floor more than 1 min after touching the prod or shocked in the absence of a prod did not bury the prod. Thus, close temporal contiguity between grid shock and prod contact appears necessary for burying. Nevertheless, grid-shocked rats do learn something different from prod-shocked rats, since they bury the prod less and the walls more than do prod-shocked rats when the position of the prod is changed in the test chamber (Experiment 3). 相似文献
15.
Twenty-eight male albino rats were given a single 4-sec 1-mA electric-grid-shock unconditioned stimulus (US). In the same session they received two 12-sec conditioned stimuli (CSs). One CS (explicitly unpaired) terminated 180 sec before the US began; the other (backward paired) began immediately after the US terminated. The CSs used were a 1000-Hz 85-dB tone and an 84-dB click; their roles were counterbalanced. Over the next 2 days, each CS was presented for 2 min while the rats drank from a water bottle. The backward-paired CS was found to suppress licking more than the explicitly unpaired CS. This suppression was accompanied by an increase in defensive behavior (freezing and freeze/nod) and by a decrease in other activity. The suppression did not seem to be due to a maintained or enhanced CS-orienting response reflex, nor could it be attributed to an adventitiously reinforced interfering operant. The results support the presumption made in previous reports that the lick suppression evoked by a backward CS reflected one-trial backward excitatory fear conditioning. 相似文献
16.
Rats received either forward or backward pairings of an auditory CS and shock. They were then tested for conditioned suppression to the CS while barpressing for food, licking a sucrose solution, or being spontaneously active. Behavior was simultaneously observed using a time-sampling method. In each case, forward-conditioned animals exhibited more freezing than controls, and freezing was reliably correlated with suppression of the baseline. These results suggest that the different loss-of-baseline measures of aversive conditioning reflect the amount of defensive behavior evoked by the CS. They also suggest the utility of freezing as an index of conditioning. Freezing assayed by the time-sampling method was comparable to the more conventional indices of conditioning in sensitivity to the effects of conditioning. 相似文献
17.
Hooded rats and golden hamsters were shocked by one of two prods in a chamber with a sawdust-covered floor. Rats buried the prod through which they had been shocked, but hamsters displayed no burying behavior. Hamsters may not have buried the prod because they could not perform the required motor pattern. However, hamsters can carry and pile food pellets. Therefore, in a second experiment, rats and hamsters were shocked in a chamber with wooden blocks on the floor. Rats piled blocks around the prod through which they had been shocked, but hamsters did not. The third experiment established that, like rats, hamsters can associate a prod with shock in one trial, since they showed differential avoidance of a prod through which they had been shocked. Since hamsters are nonsocial and rats are social, these results are consistent with suggestions that burying sources of aversive stimulation evolved as an altruistic behavior. 相似文献
18.
Jean S. Hendry 《Learning & behavior》1982,10(4):476-482
The effects of compounding two conditioned stimuli (CSs), each of which had been extinguished to varying degrees in different groups of rats given identical acquisition training, was examined within the conditioned emotional response paradigm. Greater suppression to the compound than to the individual CSs was observed following 6, 12, 48, 72, and 96 stimulus extinction trials, although after only 12 extinction trials suppression to the individual stimuli was no longer observed. The amount of compound suppression decreased progressively as the number of extinction trials increased until, after 120 extinction trials on each stimulus, the compound no longer elicited observable suppression. Control group data indicated that the observed summation effect could not be attributed to disinhibition. The possible role of the summation of undetected excitation in studies examining configurai conditioning, avoidance conditioning and reinstatement is discussed briefly. 相似文献
19.
Pavlov (1927/1960) reported that following the conditioning of several stimuli, extinction of one conditioned stimulus (CS) attenuated responding
to others that had not undergone direct extinction. However, this secondary extinction effect has not been widely replicated in the contemporary literature. In three conditioned suppression experiments with rats,
we further explored the phenomenon. In Experiment 1, we asked whether secondary extinction is more likely to occur with target
CSs that have themselves undergone some prior extinction. A robust secondary extinction effect was obtained with a nonextinguished
target CS. Experiment 2 showed that extinction of one CS was sufficient to reduce renewal of a second CS when it was tested
in a neutral (nonextinction) context. In Experiment 3, secondary extinction was observed in groups that initially received
intermixed conditioning trials with the target and nontarget CSs, but not in groups that received conditioning of the two
CSs in separate sessions. The results are consistent with the hypothesis that CSs must be associated with a common temporal
context during conditioning for secondary extinction to occur. 相似文献
20.
Stimuli associated with primary reinforcement for instrumental behavior are widely believed to acquire the capacity to function as conditioned reinforcers via Pavlovian conditioning. Some Pavlovian conditioning studies suggest that animals learn the important temporal relations between stimuli and integrate such temporal information over separate experiences to form a temporal map. The present experiment examined whether Pavlovian conditioning can establish a positive instrumental conditioned reinforcer through such temporal integration. Two groups of rats received either delay or trace appetitive conditioning in which a neutral stimulus predicted response-independent food deliveries (CS1→US). Both groups then experienced one session of backward second-order conditioning of the training CS1 and a novel CS2 (CS1–CS2 pairing). Finally, the ability of CS2 to function as a conditioned reinforcer for a new instrumental response (leverpressing) was assessed. Consistent with the previous demonstrations of temporal integration in fear conditioning, a CS2 previously trained in a trace-conditioning protocol served as a better instrumental conditioned reinforcer after backward second-order conditioning than did a CS2 previously trained in a delay protocol. These results suggest that an instrumental conditioned reinforcer can be established via temporal integration and raise challenges for existing quantitative accounts of instrumental conditioned reinforcement. 相似文献