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.     

Inescapable shock interferes with the acquisition of a low-activity response in an appetitive context

This study investigates the effects of exposure to inescapable shock on the acquisition of a low-activity appetitive response using a trial procedure. Inescapable shock was found to interfere with the acquisition of a nose-poke response to obtain food as compared with animals exposed to either escapable shock or no shock. In addition, general activity levels were measured separately during the trial and the intertrial interval during the appetitive test. Inescapably shocked animals were less active during the trial component than were either the escapably shocked or the nonshocked animals. However, no differential levels of activity were observed during the intertriai interval component of the appetitive test. The relevance of these findings for both the learned helplessness and the learned inactivity hypotheses is discussed.     

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.     

Conditioned fear and neophobia following inescapable shock

Lick-suppression tests were used in seven experiments to assess the transsituational transfer of fear in the learned helplessness paradigm. Two sources of fear combined to suppress test drinking in inescapably shocked rats. A situational odor was strongly associated with shock pretreatments and mediated the transfer of conditioned fear during testing. Fear of the pretreatment odor was greater following inescapable shock than after escapable shock or restraint. This conditioned suppression was retained for at least 72 h after pretreatment. Neophobia was enhanced as a second, nonassociative reaction to inescapable shock. Unconditioned fear was augmented by a novel odor in the test context, but otherwise was weak and dissipated within 72 h. However, neophobia was necessary for differential conditioned suppression in inescapably shocked rats. The pretreatment odor elicited fear only when tested in a novel context. Initial habituation to the test apparatus reduced conditioned fear. These data provide additional evidence for odor-mediated transfer of helplessness. Conditioned fear and neophobia are discussed in relation to recent anxiety interpretations of the phenomenon.     

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.     

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.     

Reinstatement of fear to an extinguished conditioned context

Rats were shocked in the black but not the white compartment of a shuttlebox and then exposed to the black compartment in the absence of the shock unconditioned stimulus (US) to extinguish fear responses (passive avoidance). In five experiments, rats were then shocked in a reinstatement context (distinctively different from the shuttlebox) to determine the conditions that reinstate extinguished fear responding to the black compartment. Rats shocked immediately upon exposure to the reinstatement chamber failed to show either reinstatement of avoidance of the black compartment or fear responses (freezing) when tested in the reinstatement chamber. In contrast, rats shocked 30 sec after exposure to the reinstatement chamber exhibited both reinstatement of avoidance of the black compartment and freezing responses in the reinstatement chamber (Experiment 1). Rats shocked after 30 sec of exposure to the reinstatement chamber but then exposed to that chamber in the absence of shock failed to exhibit reinstatement of the avoidance response and did not freeze when tested in the reinstatement chamber (Experiment 2). Rats exposed to a signaled shock in the reinstatement chamber and then exposed to that chamber in the absence of shock also failed to exhibit reinstatement of the avoidance response (Experiment 5). These rats showed fear responses to the signal but not to the reinstatement chamber. Finally, rats exposed for some time (20 min) to the reinstatement chamber before shock exhibited reinstatement of the avoidance response but failed to freeze when tested in the reinstatement chamber (Experiments 3 and 4). These results are discussed in terms of the contextual conditioning (Bouton, 1994) and the US representation (Rescorla, 1979) accounts of postextinction reinstatement.     

Counterconditioning of shock by a water reinforcer in rabbits

Three experiments studied the counterconditioning of certain properties of eyeshock in rabbits by establishing the shock as an appetitive CS for a jaw-movement response reinforced by intraoral water injections in a Pavlovian conditioning procedure. Although Experiment 1 demonstrated that such appetitive conditioning did not attenuate the unconditioned eyeblink elicited by the shock, it reduced the capacity of the shock to suppress leverpress responses reinforced by direct water injections in a signaled punishment procedure in Experiment 2. By contrast, when instrumentally reinforced licking was punished by eyeshock in Experiment 3, no such reduction in the suppressive capacities of the shock was found. The results were considered in terms of whether counterconditioning alters the response-eliciting or motivational and reinforcing properties of the shock.     

Immediate shock,passive avoidance,and potentiated startle: Implications for the unconditioned response to shock

Three experiments were performed to study the immediate-shock freezing deficit, a deficit in freezing in rats that results when electric shock is delivered immediately upon exposure to a novel context. This deficit was accompanied by failures to detect evidence of passive avoidance (Experiment 1) or potentiation of the auditory startle response (Experiment 2). The deficit in freezing was attenuated by preexposure to the shocked context (Experiment 3). The results support the view that fear-related behaviors are activated by signals for shock rather than by shock itself. They also suggest that the immediate-shock freezing deficit is due to a failure to process the to-be-conditioned contextual cues (Fanselow, 1986a, 1990).     

Inescapable shock and food-competition dominance in rats

Inescapable electric shock disrupts escape-avoidance learning in another apparatus. This study demonstrates a deficit in a nonlearning task in which no aversive stimulus occurs. In Experiment 1, inescapable shock lowered rats’ dominance in a food-competition situation relative to restrained controls. In Experiment 2, inescapable shock lowered rats dominance in the same food-competition situation relative to a group that received the equivalent amount of escapable shock, demonstrating that the inescapability of the shock caused at least part of the decrement observed in Experiment 1. Experiment 3 does not find that inescapable shock caused a significant difference in food consumed or running time when the rats were tested alone, showing it unlikely that the dominance effects were caused by decreased hunger or reduced running following inescapable shock.     

Generality of the failure-to-escape (helplessness) phenomenon in rats

A series of four experiments investigated a number of parameters reported to produce “helplessness” in rats. Consistent differences in escape behavior were not found between inescapably shocked and restrained rats when a FR 1 shuttling response was used. Escape latencies also did not differ between groups when a reduced shock intensity was employed during escape training in FR 2 procedure or when an increased FR 3 response was employed during escape training. Findings are discussed in terms of the robustness of the failure-to-escape phenomenon from which “helplessness” in the rat is inferred.     

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.     

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.     

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.     

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.     

Comparison of various flooding procedures in reducing fear and in extinguishing jump-up avoidance responding

Two experiments examined the effectiveness of three variations in flooding techniques on hastening extinction of a jump-up avoidance response (Experiment 1) and on reducing fear (Experiment 2) as assessed by the multivariate fear-assessment techniques of Corriveau and Smith (1978). Traditional flooding involved blocking the subject’s response by making the safety ledge unavailable; barrier flooding involved inserting a Plexiglas barrier in front of the safety ledge to make it inaccessible and moving the wall periodically during treatment; no-barrier flooding involved allowing subjects to jump onto the ledge periodically but, if they did so, immediately dumping them back onto the grids. In both experiments, all three flooding treatments were found to be more effective than a home cage treatment, although the no-barrier procedure was significantly more effective than the other two. In addition, activity measures revealed interesting and significant group differences in the patterns of activity shown during treatment.     

Role of shock intensity in the learned helplessness paradigm

Although there have been many studies of the interference effect produced by exposure to inescapable shock, little is known about the role of shock intensity. This experiment factorially manipulated four levels of shock intensity during exposure to inescapable shock and three levels of intensity during the test for interference. Interference occurred at each training shock intensity when training and test shocks were similar. Interference was not obtained when training intensity was high but testing intensity low or medium or when training intensity was low or medium and test intensity was high. These findings pose problems for learned helplessness, learned inactivity, competing motor response, and catecholamine depletion hypotheses of the interference effect in the rat.     

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.     

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).     

Spontaneous recovery in cross-motivational transfer (counterconditioning)

In two experiments with rat subjects, we examined the effects of a retention interval on performance in two conditioning paradigms in which a conditioned stimulus (CS) was associated with different unconditioned stimuli (USs) in successive phases of the experiment- Experiment 1 was designed to examine aversive-appetitive transfer, in which the CS is associated with shock and then food; Experiment 2 was designed to examine appetitive-aversive transfer, in which the CS is associated with food and then shock. Aversive and appetitive conditioned responses (freezing and head-jerk responding, respectively) were scored from videotape. In both experiments, a 28-day retention interval following the end of Phase 2 caused a recovery of the Phase 1 response and a resuppression of the Phase 2 response. The results suggest that the original association is not destroyed when the CS is associated with a new US in Phase 2. They also suggest that both retroactive and proactive interference effects may result-from interference with performance output rather than a disruption or loss of what is learned during or stored from the target phase.