Noncontingent Shock Research Articles

Enhancement of conditioned fear during extinction

Eight rats were given five sessions each of noncontingent shock at 2-, 3-, and 4-min intervals, followed by five sessions of extinction. The rats were immobile longer during the first two sessions of extinction than they were during the final two sessions of fear conditioning. The incubation effect was attributed to the prospective function as distinct from the retrospective function of the CS.

The Kamin effect as a function of time of training and associative-nonassociative processes

In Experiment 1, for animals trained in the morning, Kamin effects (U-shaped retention functions) were obtained for groups receiving active avoidance training (AA) or noncontingent shocks in the avoidance apparatus (PNC), but not for animals receiving noncontingent shocks in a separate apparatus (TNC). For animals trained in the afternoon, the retention functions observed were monotonic in all cases (i.e., no Kamin effects were obtained). Experiment 2 compared groups that received avoidance training and retention testing in the same apparatus with groups that were trained and tested in a different apparatus. A Kamin effect was observed for the former groups but not for the latter.

Alleviation of anisomycin-induced amnesia by pre-test treatment with lysine-vasopressin

Amnesia in mice for a passive avoidance response induced by anisomycin injection immediately after training was reversed by 40 micrograms of lysine-vasopressin given one hour before testing. Control groups receiving non-contingent shock instead of training were used to demonstrate that the effects of vasopressin were due to memory of shock received in a particular place, rather than non-specific suppression of locomotion. The effects of vasopressin on retention were not mimicked by either pentylenetetrazol or epinephrine suggesting that the enhanced latencies were probably not the result of increases in fear or arousal. These data support the hypothesis that the retrieval of memory can be facilitated by vasopressin. The possibility of a relationship between the effects of vasopressin and those of catecholamine manipulations on memory is discussed.

Defensive behavior and passive avoidance learning in rats and gerbils

Rats and gerbils were found to differ in defensive behavior in three situations. In Experiment 1, rats tended to crouch motionless in an open-field environment. Gerbils were more active and made more contact with objects. Experiment 2 compared the effect of noncontingent shock on the probability of five behaviors in the two species. Shock increased freezing in rats but had a less pronounced effect on freezing in gerbils. Experiment 3 showed superior passive avoidance performance in rats. The importance of testing the generality of theories of defensive behavior and avoidance learning through comparative research is discussed.

Reversal of anisomycin-induced amnesia by the ergot derivative Hydergine

The ergot alkaloid Hydergine was tested for its ability to reverse an amnesia for approach-avoidance training. Thirsty mice were trained to drink in a test chamber and then punished with brief electric shocks for drinking. Those mice injected with the protein-synthesis inhibitor anisomycin immediately after training were amnesic for the shock when tested 48 h later. Pre-test injection of 10.0 or 1.0 mg/kg of Hydergine effectively reversed the amnesia while 0.1 mg/kg was ineffective. Non-contingent shock control groups ruled out the possibility that the effect was due to non-specific effects of the drug or training stimuli.

Motor debilitation, short- and long-term shuttlebox deficits, and brain monoamine changes following footshock pretreatment in rats

Male hooded rat triplets, each consisting of an unshocked control (C), an animal that could escape from the shock by leverpressing (LE), and a yoked animal that received noncontingent shock (NC), were pretreated with either short-duration, high-intensity (Hi) or long- duration, low-intensity (Lo) footshock. Varying degrees of motor debilitation not offset by the escape contingency were apparent immediately following the Hi pretreatment. Only the rats showing motor debilitation had short-term deficits in FR-1 and FR-2 escape-avoidance performance that were related to lowered diencephalic norepinephrine (NE) levels. The Lo pretreatment, which utilized shocks ⩾5.0 sec in duration, had no significant long-term effects on escape-avoidance behavior under the conditions of this study. Only nondebilitated NC rats from the Hi pretreatment condition showed a reliable deficit in FR-2 shuttlebox performance at 72 h. This occurred in spite of the fact that their pretreatment shocks were shorter than 5.0 sec in duration and that they showed no signs of motor debilitation and essentially normal brain NE levels at 30 min.

Ethanol-induced analgesia in rats selectivity bred for ethanol sensitivity

Two rat lines selectively bred for ethanol-induced depression of locomotor activity were studied for ethanol-induced analgesia. The effects of ethanol on startle amplitude, extent of overt movements and incidence of audible vocalizations in response to intermittent, noncontingent foot shock. All three responses were dose-dependently depressed by ethanol (0.66 to 2.0 g/kg, IP), and to greater extent in the "most affected" line (MA) than in "least affected" (LA) rats. Ethanol-induced response decrements were reinstated at higher shock intensities, indicating a sensory (i.e., analgesic) rather than a motoric or analgesic basis for these effects. Genes which influence ethanol's motoric effects might, in part, influence sensitivity to its sensory effects.

The effects of scopolamine on three different types of suppressed behavior of rats

Twelve albino rats were trained to lever press on a variable-interval one min schedule for sweetened condensed milk reinforcement. While responding on this schedule a two minute tone was presented. For one group it signalled a response contingent shock (Punishment), for another group it signalled the delivery of an unavoidable non-contingent shock at its termination (CER) and for a third group, reinforcement was witheld during the tone (Extinction). In the first experiment scopolamine in doses of 0.8 to 12.8 mg/kg did not alter response rates during the tone for any group. In a second experiment 16 hooded rats were tested with 6.4 mg/kg of scopolamine using a similar procedure, but with different shock levels, apparatus, reinforcement and session duration. For all three groups the drug depressed responding during the tone. It was concluded that when all other aspects of the situation are equated scopolamine will produce the same effect on behavior suppressed by punishment, CER and extinction.

Age-dependent effects of preconditioning aversive experiences on the retention of conditioned fear in weanling rats

Two experiments investigated the effect of prior noncontingent shock experience upon the retention of fear in young rats. Rats given Pavlovian fear conditioning at 20 days of age and tested 2 or 4 weeks later showed less forgetting if they had received preconditioning shocks in infancy. The magnitude of this protection effect was inversely related to the age at which the prior experience had occurred. As preshock treatments did not appear to affect acquisition, the improved retention does not seem to be based upon changes in original learning. Early experience may enhance memory processes by increasing cue utilization.

PARTIAL AVOIDANCE CONTINGENCIES: ABSOLUTE OMISSION AND PUNISHMENT PROBABILITIES1

Avoidance contingencies were defined by the absolute probability of the conjunction of responding or not responding with shock or no shock. The "omission" probability (rho(00)) is the probability of no response and no shock. The "punishment" probability (rho(11)) is the probability of both a response and a shock. The traditional avoidance contingency never omits shock on nonresponse trials (rho(00)=0) and never presents shock on response trials (rho(11)=0). Rats were trained on a discrete-trial paradigm with no intertrial interval. The first lever response changed an auditory stimulus for the remainder of the trial. Shocks were delivered only at the end of each trial cycle. After initial training under the traditional avoidance contingency, one group of rats experienced changes in omission probability (rho(00)>0), holding punishment probability at zero. The second group of rats were studied under different punishment probability values (rho(11)>0), holding omission probability at zero. Data from subjects in the omission group looked similar, showing graded decrements in responding with increasing probability of omission. These subjects approximately "matched" their nonresponse frequencies to the programmed probability of shock omission on nonresponse trials, producing a very low and approximately constant conditional probability of shock given no response. Subjects in the punishment group showed different sensitivity to increasing absolute punishment probability. Some subjects decreased responding to low values as punishment probability increased, while others continued to respond at substantial levels even when shock was inevitable on all trials (noncontingent shock schedule). These results confirm an asymmetry between two dimensions of partial avoidance contingencies. When the consequences of not responding included occasional omission of shock, all subjects showed graded sensitivity to changes in omission frequency. When the consequences of responding included occasional shock delivery, some subjects showed graded sensitivity to punishment frequency while others showed control by overall shock frequency as well.

Central cholinergic involvement in behavioral hyper-reactivity

The present experiments were designed to test the hypothesis that behavioral reactivity to changes of environmental stimulation varies concomitantly with changes induced acutely by pharmacological and chronically by morphological manipulations of acetylcholine in the central cholinergic system. Acute reduction of acetylcholine levels was achieved by cerebroventricular injections of hemicholinium-3 at five dosages and chronic reduction by electrolytic lesions in the septum. Significant and quantitatively equivalent hyper-reactivity occurred when animals were exposed to a variety of stimulus changes at peak effect times for the two experimental treatments. Such concordance of behavioral effects was not observed during non-contingent shock stimulation, when septal animals were significantly hyper-reactive and hemicholinium-3 animals were not. These findings may be interpreted in terms of results of recent multivariate analyses showing that several independent behavioral factors constitute the septal “syndrome”: a particular factor, e.g., reactivity, may be related to a neurochemical substrate which is not shared by other factors. The present experiments revealed a highly precise relation between acute changes in acetylcholine levels and dose effect trends in hyper-reactivity, i.e., hyper-reactivity followed hemicholinium-3 injections (IVt) which reduced acetylcholine and returned to control levels when acetylcholine recovered. Under conditions of chronic acetylcholine reduction (septal lesion) initial hyper-reactivity disappeared with time, an observation consistent with the “imbalance” hypothesis about interactions between transmitter systems which assumes that changes in one system may be followed by compensatory changes in a related system.

Effect of response-contingent vs. noncontingent shock on ducklings’ preference for novel imprinting stimuli

Individual ducklings received electrical shock in the presence of an imprinting stimulus whenever they pecked at food. Other ducklings received an identical series of shocks in the presence of an imprinting stimulus, but for them shock delivery was independent of their pecking behavior. In a subsequent session, the use of shock was discontinued and all birds were afforded the opportunity to approach either the imprinting stimulus (i.e., the stimulus previously present during shock) or a novel imprinting stimulus that was simultaneously presented. Ducklings that were shocked when they pecked at food either exhibited no preference or they preferred the original imprinting stimulus. In contrast, birds for whom shock was independent of their feeding behavior preferred the novel stimulus. These findings imply that the delivery of shock in the presence of an imprinting stimulus can endow the stimulus with conditioned aversive properties. They also imply that the stimulus will acquire little or no aversiveness if shock delivery is contingent upon a specific response such as pecking.

LEVER ATTACKING AND PRESSING AS A FUNCTION OF CONDITIONING AND EXTINGUISHING A LEVER‐PRESS AVOIDANCE RESPONSE IN RATS1

Six experimental rats were conditioned to press one of two available levers to avoid shock. The levers registered bites as well as presses. For four of these rats, shock was contingent on lever bites when a specified time period had elapsed after the previous shock. An extinction period, in which only periodic noncontingent shocks were presented, followed avoidance training. Six yoked-control rats received the same sequence of shocks as did the corresponding experimental rats in both the conditioning and extinction phases. All six experimental rats repeatedly bit the avoidance lever. Four bit it more than the nonavoidance lever during conditioning, and five bit it more during extinction. Five of the six experimental rats consistently bit the levers many more times during each session than did their respective control rats, suggesting that avoidance conditioning facilitated lever biting. Rates of lever biting and pressing by all of the experimental rats and by some of the control rats were highest immediately following shock throughout both phases. During later portions of the intervals following shock, characteristic effects of conditioning and extinction were observed. This finding suggests that extinction of avoidance behavior by unavoidable shock presentations can be demonstrated more readily when shock-elicited responding is extricated from the data.

Long-Term Effects of Prior Experience in Attenuating Amnesia

In Experiment I, prior experience with passive-avoidance training followed by latent extinction was given 1, 3, 5, or 15 days before criterion (re) training and an amnesic treatment. It produced nearly complete protection from retrograde amnesia at the three shorter intervals; at the longest interval, amnesia was present but less severe than in a control group without the familiarization. In Experiment II, prior experience was given 1, 5, or 15 days before a noncontingent shock and an amnesic treatment. Evidence of a reactivation of memory was obtained only at the longest interval. Thus, familiarization and reactivation seem to represent different processes. The results are interpreted as consistent with explanations stressing the disruption of retrieval in retrograde amnesia.

Time-dependent changes in activity, reactivity, and responsivity during shock: Effects of cholinergic and catecholaminergic manipulations

A review of problems inherent in the evaluation of the nonassociative effect of shock is presented. This is followed by a series of experiments intended to evaluate time-dependent changes in activity, reactivity (i.e., activity after reintroduction of the stressor) during intershock periods, and activity during shock itself, under conditions where associative influences are minimal. Regardless of whether initial training involved response-contingent or noncontingent shock, or whether shock was signaled or unsignaled, a U-shaped reactivity function was observed during the test, with lowest levels of activity occurring 1–4 hr after initial training. The U-shaped function was considerably less pronounced if shock was not delivered during the test. The form of the function varied somewhat depending on the presence or absence of a warning stimulus, as well as on whether shock was response dependent or independent. Moreover, the period of lowest reactivity varied as a function of the number of shocks administered during pretraining. Unlike the function seen during intershock periods, activity measured during shock was found to decline monotonically as the test-retest interval increased. Treatment with scopolamine or physostigmine eliminated both time-dependent changes, suggesting involvement of cholinergic mechanisms. Although chlorpromazine eliminated both functions, treatment with d-amphetamine produced several paradoxical effects, precluding definitive conclusions regarding catecholaminergic involvement in the time-dependent changes observed.

Retention of aversively motivated behavior: Effects of time of training and associative versus nonassociative processes

Three experiments were performed to investigate time-based retention performance in aversively motivated behavior. In Exp. 1 separate groups of rats received one-way active avoidance or yoked noncontingent footshock training at 4 pm either 0.25, 6, 12, 18, 24, or 30 hr prior to one-way active avoidance testing. The data revealed neither of the two most commonly observed retention functions (i.e., U-shaped “Kamin effect” or a multiphasic pattern). In Exp 2 the same procedure was employed except all subjects were trained at 9 am. A multiphasic pattern of retention performance for both active avoidance and noncontingent shock groups was observed. Experiment 3 employed a “truly noncontingent” control procedure. Results indicated that the retention functions observed in Exp 2 were primarily due to associative rather than nonassociative processes.

Facilitation of discriminated lever-press avoidance by noncontingent shocks

Two experiments investigated the effect of presenting a brief noncontingent, unsignaled shock prior to warning-signal onset on discriminated lever-press avoidance behavior in rats. The main finding was that noncontingent shock delivered 2 sec but not 16 sec prior to warning-signal onset facilitated avoidance performance and learning. These results were predicted on the basis of shock-elicited response bursting which was expected to increase the operant level of the lever-press response at short shock-warning signal intervals. It was suggested that species-specific limitations on rats' lever-press avoidance are not unconditional, but rather can be overcome with environmental manipulations.

Stress-Induced Alcohol Consumption: A New Paradigm<xref ref-type="fn" rid="fn1">††</xref>

32 female albino rats were fluid-deprived and were given 15-minute non-contingent shock sessions on alternate days of the experiment. Half of the animals had either alcohol or sucrose solution to drink on days when they were shocked, and on other days they had plain water to drink. For the other half, water was paired with shock, and either alcohol or sucrose solution was available on alternate days. Within each of these conditions, the fluid was available for 15-minutes immediately before the shock sessions for half of the animals and for 15-minutes immediately following the shock sessions for the other half. In addition, 8 animals were run which were never exposed to shock. During test days when both alcohol and sucrose solution were available, the animals which had had liquid available before their shock sessions consumed more alcohol than those animals which had had liquid available after the shock sessions (p>0.05). These results suggest that alcohol is drunk in order to alleviate anxiety, which antedates a stressful situation, rather than as a ‘healing’ agent after stress has already been experienced.

The effects of Pavlovian CSs on two food-reinforced baselines— with and without noncontingent shock

Two experiments explored the effects of Pavlovian (tone-shock) CS+, CS−, and truly random control (TRC) contingencies on two different food-reinforced instrumental baselines. One food-reinforced baseline contained noncontingent shock, while the other did not. In the first experiment, a TRC contingency was shown to produce suppression of food-reinforced responding, while a CS− contingency did not. When noncontingent shock was added to the baseline, however, the TRC stimuli failed to produce suppression, and the CS− contingency increased response rates over baseline level. In a second experiment, the effects of TRC and CS+ contingencies were compared on these same two baselines. While the CS+ produced suppression on both shock and no-shock baselines, the TRC contingency again produced suppression on only the no-shock baseline.

Effects of prior aversive experience upon retrograde amnesia induced by hypothermia

Two experiments examined the extent to which retrograde amnesia (RA) is attenuated by prior learning experiences. In Experiment 1, rats initially received either passive avoidance training in a step-through apparatus, exposure to the apparatus, or noncontingent footshock. When training on a second but different passive avoidance task was followed by hypothermia treatment, RA was obtained only in the latter two groups. In Experiment 2, one-way active avoidance training, yoked noncontingent shocks, or apparatus exposure constituted the initial experience. Subsequent step-down passive avoidance training and amnestic treatment resulted in memory loss for the prior apparatus exposure group, but not for either of the preshocked conditions. These experiments demonstrate that certain types of prior aversive experience can substantially modify the magnitude of RA, and, in conjenction with other familiarization studies, emphasize a paradox for interpretations of RA based solely upon CNS disruption. The possibility that hypothermia treatment serves as an important contextual or encoding cue necessary for memory retrieval was considered. It was suggested that prior experience may block RA by enabling rats to differentiate training and treatment conditions.