Control over noxious events and choice

Three experiments are reported assessing whether rats prefer controllable over uncontrollable aversive shock. In Experiment 1, subjects chose between escapable and inescapable shock while relative shock duration varied parametrically. In Experiment 2, subjects again chose between escapable and inescapable shock, but duration was held constant and equal. The final experiment gave subjects a choice between avoidable and unavoidable shock under several signaling conditions. Choice behavior proved sensitive to relative shock duration and to predictability of shock but not to controllability of shock.     

Stimulus control of immunization against chronic learned helplessness

Two experiments investigated the effectiveness of multiple (five) sessions of signaled eseapable-shock pretraining in preventing (immunizing against) the shack-escape impairment produced by an equal number of sessions of signaled inescapable shock. In Experiment 1, rats were exposed to 50 pairings per session of a white-noise stimulus with escapable shock during the immunization phase. Subsequently, they were exposed to 50 pairings per session of a different (houselight) stimulus with inescapable shock. Shock-escape performance in a shuttlebox test with constant illumination revealed no evidence of immunization relative to the performance of rats given five prior sessions of light-signaled inescapable shock only. Experiment 2 was identical in all respects to Experiment 1, except that both the escapable- and the inescapable-shock phases for animals in the immunization treatment group involved the same stimulus (houseüght) as a shock signal. Under these circumstances, the prior escapable-shock training significantly reduced the shuttle-box escape deficit engendered by chronic exposure to signaled inescapable shock; performance in the shuttle-box was not reliably different from that of rats exposed to signaled escapable shock alone. These findings suggest that, under chronic conditions, the development of stimulus control using Pavlovian conditioning procedures may serve to modulate the normally prophylactic influence on later shock-escape acquisition of serial exposure to escapable and inescapable shocks.     

Inescapable shock interferes with the acquisition of an appetitive operant

This article reports the reinforcer generality of the interference effect resulting from exposure to inescapable shock. In Experiment 1, rats that received inescapable shock showed weak interference with the acquisition of an appetitive operant compared to animals exposed either to escapable or no shock. In Experiment 2, the response-reinforcer contingency was degraded by introducing a 1-sec delay of reinforcement on the appetitive task. Inescapable shock produced much stronger interference with the acquisition of the operant response than in Experiment 1. The results demonstrate reinforcer generality of the debilitating effects produced by inescapable shock.     

Activity during prior shock determines subsequent shock-elicited fighting in the rat

Two experiments investigated the relationship between activity during shock and the magnitude of subsequent impairment of shock-elicited fighting in the rat. Different levels of intra-shock activity were engendered in two ways. In Experiment 1, differing temporal forms of inescapable shock were employed to produce markedly different levels of activity. In Experiment 2, a passive-escape procedure was used to explicitly reinforce nonmovement during shock relative to a yoked, inescapable shock control. Results indicated that relative to the performance of subjects not previously shocked, fighting impairment was produced only by those prior treatments that promoted reduced intrashock activity. Since one of the prior shock treatments involved inescapable shock but the other did not, these findings may be viewed as strong support for the notion that behavior during shock, rather than uncontrollability, is the critical determinant of the observed impairment effects. There was some suggestion in both studies that shock treatments that resulted in sustained or increased intrashock activity tended to produce augmentation of fighting. Both inhibitory and facilitative effects of prior shock exposure are discussed in terms of an interacting response theory of shock treatment effects.     

Fear-motivated vicious-circle behavior maintained through secondary punishment

Two experiments attempted to establish vicious-circle behavior through fear motivation combined with secondary punishment. In Experiment 1, rats were trained with two CSs, a tone and a buzzer, paired with shock in different contexts. Secondary punishment based on delay and trace conditioning procedures facilitated running in fear-motivated rats, relative to four control groups. In Experiment 2, rats were given pairings of a tone CS with shock, and a buzzer CS with a drop into a water tank. Fear-motivated rats which received secondary punishment during either 33% or 100% of test trials exhibited self-punitive running relative to a nonpunished (0%) group and a backward-conditioning control group. Results indicate that “all secondary” vicious-circle behavior can be established through Pavlovian conditioning, thus supporting a conditioned fear interpretation.     

Reversal of visual discrimination problem and differential frustration effects in dominant and submissive rats

Two experiments are reported comparing performance in dominant and submissive rats as determined by a food-competition procedure. Ss in Experiment I were either trained to criterion or overtrained before being reversed on a visual discrimination task. Although the two groups did not differ significantly in learning the initial task, the dominant Ss were significantly slower on reversal than the submissives. Experiment II, which utilized a tandem runway, showed that when the reinforcer which maintained the running response was not available in the first goalbox, submissive rats responded with a greater increase in running speed in the second runway than dominant rats. These findings were discussed as reflecting motivational differences between dominant and submissive rats.     

Interference with avoidance behavior as a function of qualitative properties of inescapable shocks

Temporal form (continuous vs. pulsating) and shock source (alternating current vs. direct current) were factorially combined to produce four shock treatments. The effects of inescapable presentations of these stimuli on subsequent avoidance response acquisition were measured in dogs (Experiment 1) and in rats (Experiment 2) and revealed an interaction of shock variables. Initially, all groups that received ac shock showed impaired performance for the pulsating and continuous shock conditions; groups that received dc continuous shock were also impaired, while those that received dc pulsating shock were not. While this pattern of interference persisted for dogs, it was transient in rats, with only the ac continuous-shock group continuing to be impaired. Mean avoidance performance were positively related to mean activity levels during inescapable shocks for the dc shock groups but not for the ac shock groups.     

Escape acquisition following inescapable shock in the rat

Male rats which had received approximately 21 min of pulsed, inescapable tail shock during a 6-h session in a wheel-turn chamber were markedly deficient in acquisition of an FR 2 crossing escape response in a shuttlebox when first tested 22 or 70 h later (Experiments 1 and 2). Rats which had received identical amounts and patterns of escapable/avoidable shock, however, were not deficient (Experiment 1). Preventing wheel-turn responses during the inescapable shocks prevented the occurrence of the subsequent escape deficit, whereas reducing the feedback provided for the first crossing response of the FR 2 requirement enhanced the deficit (Experiment 3). These data can be best explained by the learned helplessness hypothesis and indicate that the types of responses available and made during the inescapable shocks are more important than previously indicated.     

Influence of conspecific stress odors and shock controllability on conditioned defensive burying

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.     

A potential shock-reducing contingency in the backshock technique: Implications for learned helplessness

Electric shocks were delivered to rats through a subcutaneously implanted back electrode. Experiment 1 evaluated the relationship between number of paws grounded and total power dissipated in the rat. In Experiment 2, the threshold of shock-induced vocalization, a putative index of aversiveness, was found to be positively correlated with the number of paws grounded. These findings suggest that when the backshock technique is used, the aversiveness of shock potentially can be modified by the posture adopted by the experimental animal. Caution should be exercised, therefore, in attributing deficits in escape behavior following inescapable shock administered with back electrodes to learned helplessness.     

The effects of order of shock durations on helplessness in rats

Whereas rats exposed to a series of progressively decreasing shock durations show deficits in shuttle-escape performance 24 h later, the same number and intensity of shocks in the reverse (increasing) order of durations does not produce the “learned helplessness” effect (Balleine & Job, 1991). We conducted two experiments to establish the generality of this shock-duration order effect on other measures of distress and helplessness in rats. In Experiment 1, rats exposed to decreasing durations of inescapable shock showed reduced consumption of quinine-adulterated water (finickiness), whereas increasing durations produced no finickiness. By contrast, increasing shock durations produced greater conditioned fear to the shock context than did decreasing shock durations in Experiment 2. The differential effects of shock-duration order on finickiness and fear are explicated in terms of the specificity of fear conditioning during exposure to increasing versus decreasing series of shock duration orders.     

Influence of duration and number of inescapable shocks on intrashock activity and subsequent interference effects

A three-phase investigation of the effects of duration and number of inescapable shocks with rats was conducted. In the first phase (shock treatment), separate groups were exposed either to 64 or 128 5-sec shocks or to 32, 64, or 128 10-sec shocks. Measures of intrashock activity were found to be lower for the groups exposed to 64 or 128 10-sec shocks than for any other group. In the second phase (Test Day 1), half of each group was tested for interference with FR 1, locomotor escape-avoidance learning at either 24 or 168 h following cessation of shock treatment, using a control procedure that was designed to equate groups for exposure to test shock. The results indicated that, relative to nonshock-treated controls, at each interval only the groups previously given 64 or 128 10-sec shocks were impaired in terms of escape frequency. However, all groups given at least 64 shocks exhibited depressed intertrial responding at the 24-h, but not the 168-h, interval. In the final phase (Test Days 2–4), the control procedure for equalizing test-shock exposure was discontinued and a pattern of interference effects was observed in terms of escape-avoidance response latency that was identical to that reported for the escape frequency in Phase 2. In general, these data were viewed as indicating that duration, but not total amount of shock, was a critical determinant of behavior during inescapable shock and of the subsequent interference effect. Both effects of duration were regarded as the product of a common associative process involving the learning of immobility tendencies to shock that served to compete with later escape-avoidance responding.     

Dominance,the bidirectional hypothesis,and Pavlovian backward conditioning in the US-US paradigm

Based upon considerations raised by Soviet research, the role of relative stimulus intensity, or dominance, in the unconditioned stimulus-unconditioned stimulus (US-US) paradigm was investigated under circumstances presumed favorable to the backward conditioned response (CR). Using the classically conditioned forelimb response of the cat, a brief shock (USD delivered to one forepaw preceded a shock (US2) to the opposite forepaw in paired conditioning fashion; subjects in the control group received explicitly unpaired presentations of the stimuli. Conditioning in both the forward and backward directions was evaluated by the appearance of contralateral CRs on test trials to each of the USs. In Experiment 1, a ratio of the intensities between US1 and US2 of 100:80 was used to create a relative dominance in favor of the backward CR. In addition, to evaluate the suggestion that the appearance of the backward CR is retarded in the Pavlovian paradigm, overtraining was provided to a forward conditioning criterion of 200%. In Experiment 2, the cats were exposed to successive reductions in the intensity of US2 to verify manipulations of dominance reportedly involved in the reactivation of a latent backward CR. Although forward conditioning was readily established to USl, there was no evidence of back-ward conditioning to US2 under any of the conditions.     

The nature of the initial coping response and the learned helplessness effect

The availability of an effective coping response has been shown to attenuate the deleterious behavioral and physiological consequences of inescapable electric shock. In the current study, two groups of rats could escape tailshock by turning a wheel. When short-latency responses that appeared to be elicited by shock onset were permitted to terminate shock, rats subsequently failed to learn to escape in a shuttlebox and did not differ from rats which received an equivalent amount of inescapable shock. However, when a relatively long-latency response was required and short-latency responses were not allowed to affect shock, rats subsequently readily learned to escape in the shuttlebox. The implications of these results for explanations of the manner in which prior exposure to shock influences subsequent escape learning were discussed.     

Effects of stress controllability,immunization, and therapy on the subsequent defeat of colony intruders

Three experiments investigated the influence that various stress-controllability manipulations had on the defensive behaviors of rats when they were subsequently tested as intruders in previously established, aggressive colonies of conspecifics. In Experiment 1, naive subjects that had received a session of 80 shocks in a tube showed an enhanced series of defensive responses and received more bites than did a group of restrained nonshocked rats as colony intruders 24 h later. These two measures were also found to be positively correlated within each group. In Experiment 2, a group that was given 80 yoked inescapable shocks, in contrast to a group that had wheel-turn escape training and a restrained nonshocked control group, displayed more defeat and was bitten more frequently when tested as intruders on the following day. In Experiment 3, 60 trials of wheel-turn escape training were given 4 h prior to (i.e., immunization) or after (i.e., therapy) a session of 60 inescapable tube shocks. During resident-intruder testing 24 h later, both of these groups showed less defeat and received fewer bites than did an inescapably preshocked group but did not differ from a restrained nonshocked control group. These findings clearly indicate that stress controllability alters species-typical defensive responses, and their implications concerning other learned helplessness effects and interpretations are discussed.     

The nature of the activity deficit produced by inescapable shock

Two experiments investigated the nature and etiology of the reduced activity in the presence of shock produced by prior exposure to inescapable shock. Previous experiments have demonstrated this deficit in the presence of gridshock. However, gridshock hurts less if movement across the grids is reduced. It is thus unclear whether the inescapable-shock-produced deficit represents a facilitation of learning to reduce movement across the grids in order to alleviate pain or is an “unconditioned” reduction in movement in response to shock. The first experiment tested these possibilities by examining the effects of inescapable shock on subsequent movement during shock delivered via fixed tail electrodes to freely moving subjects. Inescapably shocked subjects still moved less in response to shock than did escapably shocked and restrained control subjects. Experiment 2 examined the possibility that this deficit occurs because unconditioned movement in response to shock during pretreatment diminishes after a few seconds, the reduction then being adventitiously reinforced by shortly ensuing shock termination. Activity during inescapable shock was closely monitored by ultrasonic motion detection. Although activity did decrease across trial blocks, the required within-trial patterns did not occur. Shock-elicited activity did not diminish after a few seconds of shock, but remained unchanged across the 5-sec shock presentations.     

Influence of conspecific and predatory Stressors and their associated odors on defensive burying and freezing responses

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.     

The learned function of food-deprivation cues: A role for conditioned modulation

Rats trained in one context to use stimuli arising from food deprivation as discriminative signals for shock were tested in other contexts to assess the basis of conditioned responding (i.e., freezing or behavioral immobility). In Experiment 1, discriminative control by 24-h food-deprivation cues failed to promote transfer responding in a test context that had no association with shock. This indicated that food deprivation cues had little direct excitatory power. However, transfer of behavioral control by 24-h food-deprivation cues was obtained in a context paired with shock only when the rats were 19 h water deprived. This finding agrees with the idea that food-deprivation cues become conditioned modulators of the capacity of external stimuli to activate their association with an unconditioned stimulus. In Experiment 2, rats trained to use 24-h food-deprivation cues as signals for shock exhibited significantly greater transfer performance when the transfer context had undergone partial extinction relative to when the transfer context had undergone only simple excitatory training. This finding with deprivation cues and transfer contexts (1) paralleled earlier results obtained with discrete (auditory and visual) conditioned modulators and transfer targets, and (2) posed difficulties for associative summation and generalization interpretations of transfer performance.     

Influence of postpartum shock controllability on subsequent maternal behavior in rats

Responses of mother rats were observed 24 h before and 24 and 72 h after exposure to one of three 8-day postpartum treatments: shock escape training, yoked inescapable shock, or restrained with no shock. In contrast to those in the other two groups, the dams given inescapable shock showed slower speed to approach the nest, shorter durations of being on the nest, and lower frequency and shorter total duration of oral contact with their pups. These dams also retrieved their pups less frequently, but this measure, as well as the frequency of leaving the nest, did not result in significant differences between groups. Since the traditional interpretations of the learned-helplessness effect were not entirely able to account for these findings, the observed uncontrollable-stress-produced changes in maternal behavior were examined from an ethological perspective.     

The role of spatial and temporal contiguity in defensive burying in rats

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).