Shock-escape Training Research Articles

Sex differences in the behavioral consequences of inescapable footshocks depend on time since shock

In two experiments, the effects of inescapable shock on subsequent shuttle-box escape performance were studied in male and female rats. Effects of treatment with short-duration shocks (2 s) were studied after 1- and 24-hour intervals (Experiment 1), and effects of long-duration shocks (6 s) were studied after 24- and 72-hour intervals (Experiment 2). Experience with inescapable shock resulted in a serious disruption of escape performance in both males and females. A large increment in escape latencies was found both during fixed ratio 1 and fixed ratio 2 escape training; however, effects of inescapable shock were more pronounced in males than in females. In Experiment 1, sex differences were most obvious after the short 1-hour interval whereas, in Experiment 2, sex differences were only present after 24 hours and not after 72 hours. Shuttle activity during 2-min adaptation prior to shock-escape training was reduced in both males and females treated with IS, and this effect was somewhat stronger in males than in females. The data of these experiments show that male rats are more sensitive to the consequences of exposure to inescapable aversive stimulation than female rats. It is proposed that the time-dependency of the sex differences in behavioral consequences of treatment with inescapable shock may be related to sex differences in transient neurochemical or hormonal changes induced by inescapable shock.

Self-punitive behavior: Strength of fear of startbox and third runway segment stimuli over punished-extinction trials

According to the learning theory interpretation of self-punitive behavior, conditioned fear is critical to the maintenance of self-punitive running. In this study, fear conditioned to startbox and third runway segment cues was measured before and after punished-extinction (PE) trials. After shock-escape training, 120 male rats were given 0, 5, 10, or 20 PE trials. Fear of segment cues then was measured in either the startbox or third runway segment using hurdle-jump performance as the index of fear. The results support the conditioned-fear explanation. As predicted, immediately following shock-escape training, no difference was found between the amount of fear elicited by startbox and third segment cues, but after five or more PE trials more fear was elicited by startbox cues than by third segment cues. Additional PE trials maintained, but did not increase, the level of conditioned fear of startbox cues.

Self-punitive behavior: Fear of different alley segments

According to the Mowrer-Brown hypothesis (Brown, 1969, Punishment and Aversive Behavior), conditioned fear is critical to the maintenance of self-punitive behavior. This study investigated the effects of midsegment shock on fear of different alley segments. Sixty male rats were given shock-escape training followed by 15 trials of regular or punished extinction. Animals were then blocked in one of the alley segments and allowed to escape by jumping over a hurdle into a safebox. Hurdle-jump performance indexed the level of fear of each segment. Fear of preshock segment cues was greater than fear of shock segment and postshock segment cues, and fear of first segment cues was greater for punishedextinction subjects than for regular-extinction subjects. The results support a conditioned-fear interpretation of self-punitive behavior.

Self-punitive behavior: An independent measure of fear of the startbox

The hurdle-jumping response was used as an independent index of conditioned fear to test differences in fear of the startbox predicted by the conditioned-fear interpretation of self-punitive behavior. Following shock-escape training and varying numbers of regular- or punished-extinction trials, subjects were dropped into the startbox with access to the runway blocked and allowed to escape by jumping over a hurdle into a safebox. All subjects learned to jump the hurdle. Subjects given punished extinction showed more fear of the startbox than those given regular extinction. Startbox fear increased with the number of punished-extinctinction trials up to a point and then decreased. The results validate the use of hurdle jumping as an independent index of fear and strongly support the conditioned-fear interpretation of self-punitive behavior.

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.

Cross-stressor immunization against the behavioral deficits introduced by uncontrollable shock.

Exposure to inescapable shock disrupted performance in both shock- and water-escape tasks. These deficits were prevented in mice that were previously trained in the same task. However, an asymmetrical immunization effect was seen in a cross-stressor paradigm. Whereas deficits of water-escape performance engendered by inescapable shock were prevented by prior shock-escape training, the deficits of shock-escape performance were not eliminated by prior water-escape training. Evidently, the immunization effect occurs when initial training and subsequent testing are conducted in the same task, or when the initial training and uncontrollable stress session involve the same aversive stimulus. Norepinephrine determinations revealed that reductions of the amine introduced by inescapable shock were unaffected by prior shock-escape training and were enhanced by prior exposure to the stress of water immersion. Thus, although the performance deficit introduced by inescapable shock may be related to variations of norepinephrine, the immunization effect probably was unrelated to alterations of this transmitter. Rather, the data provisionally suggested that the immunization stems from two independent factors: Namely, initially training animals in an active escape task may (a) disrupt subsequent learning that the inescapable stress actually is uncontrollable and (b) limit the influence of the motor deficits introduced by uncontrollable shock on subsequent escape performance.

Self-Punitive Responding as A Function of Spacing of Trials in Acquisition and Extinction

After 48 rats were given massed or spaced shock-escape training in a straight runway, they were given extinction trials under massed or spaced conditions with shock present or absent in the goal box. Self-punitive responding was found under most spaced trial conditions but not under the massed-spaced or massed-massed condition. The results appear incompatible with several interpretations of self-punitive responding and consonant with a gradient of aversiveness hypothesis.

Some effects of a buzzer CS and a novel buzzer on self-punitive running in rats

Self-punitive behavior was demonstrated in prepunishment speeds during extinction following shock escape training in a straight runway under buzzer-CS and under no-CS conditions. The buzzer enhanced punished running (shock in the last half of the runway) and nonpunished running. The buzzer did not significantly enhance self-punitive behavior, defined as the difference between punishment conditions with faster running for punished rats than for nonpunished rats. Introduction of a novel buzzer at the beginning of extinction enhanced both punished and nonpunished running relative to no-CS conditions but had no effect on selfpunitive behavior. Discontinuance of the buzzer CS at the end of acquisition eliminated selfpunitive behavior during extinction. The results were interpreted as supporting explanations of self-punitive behavior in terms of fear conditioning and conflict resolution.

Some effects of methylphenidate on self-punitive running in rats

Self-punitive behavior was demonstrated in prepunishment speeds during extinction following shock-escape training in a straight runway under no-dose, low-dose (1-mg/kg), and high-dose (10-mg/kg) methylphenidate conditions. Increased dosage enhanced punished running (shock in the last half of the runway) and nonpunished running. Self-punitive behavior, defined as the difference between punishment conditions with faster running or increased persistence under punishment conditions, was not significantly affected by the drug variable. The results were interpreted as compatible with conditioned fear interpretations of self-punitive behavior but nonsupportive of cognitive interpretations.

The role of reinforcement contingencies in the maintenance of vicious circle behavior

Following 20 shock-escape training trials, two experimental groups of rats were reinforced either for running quickly (DRH animals could preclude shock in the center section of the runway by decreasing their starting latencies) or for running slowly (DRL animals could preclude shock in the center section of the runway by increasing their starting latencies). Results showed that the DRH animals ran consistently faster than the DRL animals, although no differences between DRH animals and traditionally punished extinction subjects were obtained. The results were discussed in terms of the existing explanations of vicious circle behavior, as well as in terms of the differential effects of manipulating the reinforcement contingencies on the maintenance of self-punitive running.

Some effects of type of auditory CS on self-punitive running in rats

Self-punitive behavior was demonstrated in prepunishment speeds during extinction following shock escape training in a straight runway under buzzer-CS and tone-CS conditions. Relative to the tone, the buzzer enhanced punished running (shock in the last half of the runway) and nonpunished running. These results extend the findings of Myers (1962), who reported better avoidance conditioning with a buzzer than with a tone. Self-punitive behavior, defined as the difference between punishment conditions with faster running under punishment conditions, was not significantly enhanced by the buzzer. These results do not support the suggestion (Delude, 1973) that self-punitive behavior may be uniquely affected by the use of a buzzer CS.

Acquisition and retention of multidirectional escape behavior in preweanling rats

The shock-escape behavior of preweanling rats in a multidirectional escape situation was examined in 3 experiments. In Experiment I, 5-, 7-, 9-, and 11-day-old rats were given shock-escape training on each of 3 days. Rats younger than 7 days of age did not improve escape responding within or over sessions. Animals 7 days of age and older, however, showed both an intrasession improvement and an intersession improvement that could not be attributed solely to maturation. In Experiment II, the escape behavior of 3-, 5-, and 7-day-old was examined in an apparatus modified to take into account the poor locomotor abilities of these animals. They were given escape training on 3 successive days. Again; no within-session improvement was found in rats under 7 days of age. However, an intersession improvement was found in rats whose training began at 5 days of age. This improvement was due to maturation and did not reflect a cumulative effect of training. Experiment III, like Experiment I, demonstrated that the intersession improvement in the older rats was not simply a maturation effect. It also demonstrated that the improvement could not be attributed to the stress of prior handling, shock, or body temperature loss, but was, rather, a retention effect. These results support the contention that the emergence of memory is task specific.

Dose-related effects of ethanol on avoidance-avoidance conflict behavior in the rat.

The effects of ethanol on avoidance-avoidance conflict behavior were examined, utilizing a 3- x -3 factorial design in which rats were trained and tested after drinking sugar-water solutions containing 0, 3, or 6% ethanol. Avoidance tendencies were established by initially training rats to escape from electric shock by running in one direction in a white alley, and in the opposite direction in a black alley. In subsequent shock free conflict tests, the rats were placed into an alley with one black wall and one white wall, an environment in which incompatible tendencies to avoid both ends of the alley were aroused. During training, ethanol decreased the speeds with which rats escaped shock. In the subsequent avoidance-avoidance conflict tests, rats that previously received shock escape training after drinking ethanol ran more slowly, and exhibited lower total movement and oscillation range scores than did animals trained after drinking plain sugar-water. Administration of ethanol just prior to the conflict tests resulted in dose-related increases in running speeds, total movement scores, and oscillation ranges. These results suggest that moderate doses of ethanol increased responding by differentially weakening conflicting avoidance tendencies.

Ethanol and avoidance-avoidance conflict in the rat

The effects of ethanol on avoidance-avoidance conflict behavior in a straight runway were studied in rats with a 2 by 2 design in which shock-escape training and subsequent shock-free conflict tests were administered after the animals had orally ingested either ethanol or sugar water. Rats trained under ethanol escaped shock more slowly and, during the conflict tests, approached the shock regions less closely, started and ran more slowly, and oscillated less than sugar-water-trained controls. However, rats tested under ethanol approached the shock regions more closely, started and ran more rapidly, oscillated more, and reversed direction more than rats tested when sober. No state-dependent interactions were obtained. Some of the results were consistent with a fear-reduction hypothesis, but others supported the assumption that ethanol affected the two avoidance gradients differentially.

Two-way self-punitive locomotor behavior

The effect of an explicit buzzer CS upon self-punitive locomotor behavior was investigated in an experiment utilizing a fully automated two-way locomotor device. Two groups of rats received shock-escape training and extinction, with or without the CS. During extinction, half of the animals in each group were shocked in the middle segment of the alley while the other half were given no-shock regular extinction trials. Rats trained and extinguished with the CS completed more extinction trials than those trained and extinguished without a CS, while rats punished during extinction completed more trials than rats given regular extinction trials. In addition, the punishment-produced facilitation of extinction performance was greater for rats trained and extinguished with the CS than for those without the CS.

Nonshock confinement duration and shock- and safebox similarity during escape training in rats

Sixty female hooded rats received 70 shock-escape training trials with shock- and safeboxes similar or dissimilar to each other and nonshock (safebox) confinement durations of 5 sec or 20 sec. (Shockbox confinement duration prior to shock onset was 5 sec.) In each confinement condition performance under the similar shock/safe condition was reliably poorer than that under the dissimilar condition. Safebox confinement duration negligibly affected performance under the dissimilar condition, while in the similar condition increasing confinement duration reliably facilitated performance. Comparisons with control data suggest that facilitation of escape was due to the relative shock-safe confinement duration rather than to absolute safebox confinement.

Effects of retraining following response prevention on extinction of escape behavior

Sixty female hooded rats received a sequence of 40 shock-escape training trials, 20 response prevention (or pseudoprevention) trials, either 0, 5, or 20 shock-escape retraining trials and then nonshock extinction procedures. Results of extinction using escape speed and trials-to-criterion indices showed that, in each retraining condition, response prevention reliably facilitated extinction relative to pseudoprevention controls, the degree of facilitation decreasing as amount of retraining increased. In 5-and 20-trial retraining conditions, prevention procedures also reliably impaired shock-escape performance on early retraining trials, this effect dissipating before the start of extinction.

Helplessness in hippocampectomized rats: Response perseveration?

In a test for learned helplessness, hippocampectomized rats, cortical controls, and unoperated controls were given shock-escape training after being subjected to a series of noncontingent shocks. During these preshock treatments, the same amount of gross body activity was elicited in all three groups. Compared to rats that did not receive the preshock treatments, all the preshocked animals performed poorly in shock escape; that is, hippocampals, cortical controls, and normals all exhibited learned helplessness. The fact that hippocampectomy resulted in the most marked learned helplessness is contrary to the response-perseveration interpretation of hippocampal function.

Persistence of response prevention effects following retraining of escape behavior

This study evaluated the effects of response prevention procedures on the extinction of escape behavior following the reinstatement of shock-escape training prior to the start of extinction. Female hooded rats were assigned to four groups ( N = 10) in a factorial design which orthogonally combined response prevention or pseudo-prevention procedures with escape retraining or no retraining procedures. Results showed that prevention reliably impaired shock-escape behavior on early retraining trials; but this effect dissipated completely by the end of retraining. In extinction, prevention reliably facilitated the extinction of escape behavior relative to that of pseudo-prevention controls; but the degree of facilitation was reliably attenuated by retraining procedures. These findings were related to the competing response interpretation of prevention effects.

The effects of social interaction upon persistence of self-punitive behavior

Four groups of rats were trained to escape shock in a straight runway prior to institution of punishment conditions in an attempt to assess the effect of the presence of another S upon the persistance of self-punitive behavior. All rats first received the usual 35 shock escape training trials. Then, during extinction when no shock was present in the goalbox or startbox, Ss were put into one of four groups: punished, nonpunished, punished with a naive S, and punished with another punished S. Results showed that punishment produced self-punitive behavior and that the presence of another S decreased the number of trials a punished S would perform. The presence of a naive S had more effect than the presence of a trained S. The results are discussed in terms of generalization decrement, social interaction, and fear.