Exposure to inescapable shock produces both activity and associative deficits in the rat

Interference with shuttle-box escape learning following exposure to inescapable shock is often difficult to obtain in rats. The first experiment investigated the role of shock intensity during escape training in the apparent fragility of the effect. Experiment 1A demonstrated that the magnitude of the interference effect was systematically related to shock intensity during shuttle-box testing. At .6 mA, a robust effect was obtained, whereas at .8 mA and 1.0, little or no deficit in the escape performance of inescapably shocked rats was observed. Experiment 1B demonstrated that the deficit observed in Experiment 1A depended upon whether or not rats could control shock offset. Experiment 2 suggested that preshock may suppress activity and that higher shock levels may overcome this deficit. Experiment 3 tested this as the sole cause of the escape deficit by requiring an escape response which exceeded the level of activity readily elicited by a 1.0-mA shock in both restrained and preshocked rats. In such a task, preshocked rats performed more poorly than did restrained controls. These results are consistent with the possibility that inescapable shock may, in addition to reducing activity, produce an associative deficit. Experiment 4 more clearly demonstrated that inescapable shock produces deficits in performance which cannot be expleined by activity deficits and which appear to be associative in nature. It was shown that inescapable shock interfered with the acquisition of signaled punishment suppression but not CER suppression. The theoretical implications of these data for explanations of the manner in which prior exposure to inescapable shock interferes with escape learning were discussed.     

Amphetamine, conditioned stimulus, and nondebilitating preshock effects on activity and avoidance: further evidence for interactions between associative and nonassociative changes

A literature survey and preliminary experiments with rats on the consequences of shock preexposure on subsequent activity and escape or avoidance showed the need for further work on the interactions between nondebilitating preshock and various test and treatment factors. The two main experiments used 16 preexposure conditions, namely, presence or absence of unavoidable punishment (36 shocks of 2.5 mA and 5 sec subdivided in three daily sessions), a light CS, a central partition in the shuttle-box, and dl-amphetamine sulfate (1 mg/kg ip 15 min before each session). In both experiments the four factors studied exerted more than additive effects on activity in preexposure sessions, leading to a very high frequency of crossing in the CS-shock-no-partition-drug condition. Upon retesting for activity (Experiment 1) suppression of locomotion by prior shock was less marked in animals preexposed to CS-US pairings in the absence of partition, while proactive amphetamine effects consisted mainly of a progressive increase of activity over successive retest sessions in the groups not preshocked. Upon retesting for light-cued, two-way avoidance acquisition (Experiment 2) the groups preexposed to US only were mostly retarded, while those preexposed to paired CS and US were mostly facilitated. Other changes, including drug pretreatment consequences, were negligible or unsystematic, but in general the data showed that the effects of various preexposure conditions on activity could not account for those on avoidance. Overall, it appears that the interactions between nondebilitating preshock and other test and treatment factors can be further exploited to clarify the respective roles of various associative and nonassociative mechanisms in modulation of activity and adaptive responding in aversive situations.     

Prior exposure to inescapable electric shock in rats affects extinction behavior after the successful acquisition of an escape response

In Expt 1, rats exposed to 64 inescapable electric shocks in a restrainer or merely restrained were later given either 0, 5, 15 or 30 escape/avoidance training trials with a two-way shuttlebox procedure that does not lead to interference with escape acquisition due to prior exposure to inescapable shock. After escape training all rats were given an escape/avoidance extinction procedure in which shock was inescapable. The rats which had received prior exposure to inescapable shock responded less often and with longer latencies in extinction than did the restrained rats. Experiment 2 demonstrated that this effect is caused by the inescapability of the initial shock treatment. These results were explained in terms of (a) associative interference which minimized the effect of shuttlebox escape training for the preshocked subjects, and (b) a stronger tendency to recognize the presence of an inescapable shock situation during extinction for the preshocked subjects. The relationship between these results and previous work demonstrating that exposure to the escape contingency mitigates the effects of inescapable shock exposure was also discussed.     

The time course of extinction-induced aggressive behavior in humans: Evidence for a stage model of extinction

Three experiments examined the effects of extinction on aggressive responding in male college students. In Experiment 1 subjects initially performed on a task where shuttle responding was either continuously or partially reinforced with tokens while either a nonaggressive button-pressing response or an aggressive pad-striking response was concurrently reinforced by escape from a moderately aversive tone. During shuttle acquisition there was clear preference for the escape response of button pressing, but when shuttle responding was extinguished subjects began to respond aggressively by striking the pad to escape. The time course of aggressive escape responses during concurrent shuttle extinction was an inverted U; aggressive responding rose to a peak and then declined. Aggressive responding began earlier in extinction following continuous- as contrasted with partial-reinforcement shuttle training. Experiment 2 showed that similar extinction-induced aggression was precipitated by both moderate and extended continuous-reinforcement shuttle training, with earlier onset after extended reinforcement. Experiment 3 ruled out the possibility that the emergence of the pad-striking response during extinction was simply induced response variation. These data were interpreted within the theoretical framework of P.T.P. Wong's recently advanced stage model of extinction (Animal Learning and Behavior, 1978,6, 82–93).     

Transfer of conditioned appetitive stimuli to conditioned aversive excitatory and inhibitory stimuli

The transfer of Pavlovian appetitive stimuli to Pavlovian aversive stimuli was examined in three experiments. In Experiment 1, rats received appetitive (Ap) conditioning designed to establish a flashing-light stimulus as either a CS+, CSo, or CS? for food, or to maintain it as a novel stimulus for US-alone subjects. Then, the stimulus was employed as a signal for weak shock in conditioned-emotional-response (CER) training. Both acquisition and extinction results showed that the ApCS+ facilitated and the ApCS? retarded aversive excitatory conditioning relative to the ApCSo and US-alone controls. Experiment 2 replicated the findings of Experiment 1 with both a moderate and a severe shock in CER training. In Experiment 3, different groups received the same appetitive conditioning as before, but to a flashing-light stimulus which was then employed as a signal for no shock in CER training. The ApCS? facilitated and the ApCS+ retarded aversive inhibitory conditioning relative to ApCSo and US-alone controls. Collectively, these findings establish that, in Pavlovian conditioning, transfer of an appetitive CS to an aversive excitor or inhibitor is facilitated by maintaining the initial conditioning contingency.     

Apparent Incentive Contrast Effects in Autoshaping with Rats

The effects of shifts in reward quality and quantity on Pavlovian acquisition were studied in rats. In Experiment 1, animals preexposed to unsignaled food pellets, 10% sucrose solution, or home cage controls subsequently received autoshaping training (response-independent lever-pellet or lever-solution pairings, in three groups each). Unsignaled preexposure to sucrose solution facilitated autoshaping for pellets (relative to unshifted controls), whereas unsignaled preexposure to pellets retarded autoshaping for sucrose solution. In Experiment 2, unsignaled preexposure to 30% sucrose solution impaired acquisition reinforced by food pellets, relative to 2% solution. Using a choice procedure, Experiment 3 demonstrated that rats prefer pellets to either 2 or 10% sucrose solutions, but they prefer the 30% solution to the pellets. Experiment 4 demonstrated the facilitatory effect after an upward shift in reward magnitude rather than quality (from 1 to 12 pellets), but provided weaker evidence for retardation following a downward magnitude shift. Experiment 5 was similar to Experiment 4, except that animals received autoshaping training from the outset. No evidence of successive positive contrast was obtained, but there was a significant successive negative contrast effect. Moreover, extinction was faster after acquisition with 12 pellets rather than 1. These results suggest the presence of incentive contrast effects under Pavlovian training conditions.     

Gastric ulceration and adrenocortical activity after inescapable and escapable pre-shock in rats

Two experiments are reported which investigated the effects of pre-shock treatment in rats on adrenocortical activity and susceptibility to later restraint-induced ulceration. In Experiment I, animals were exposed to a single inescapable 3 minute shock on 5 consecutive days. These shocked animals exhibited sensitisation of the adrenocortical response over days, increased adrenocortical reactivity to open field testing one week later and a trend for more severe ulceration after 20 hours of restraint. In Experiment II, animals were given 20 escapable or yoked pre-shock trials on 5 consecutive days. No sensitisation of the adrenocortical response was observed. Escape animals however were found to exhibit less gastric ulceration and a reduced adrenocortical responses after 20 hours of restraint 9 days after the last preshock session.     

Acquisition of a free-operant-appetitive response in pigeons as a function of prior experience with response-independent food

Deficits in learning to escape from electric shock following exposure to response-independent preshocks have frequently been reported and have been referred to as learned helplessness. Experiments were conducted in order to determine whether a phenomenon similar to learned helplessness could be induced in appetitive free-operant procedures with pigeons. Subjects received preliminary training under one of the following conditions; protracted exposure to response-dependent grain presentations (key pecking), protracted exposure to response-independent grain deliveries, or short-term hopper training. Subjects were then tested for acquisition of a treadle-pressing response which was the only means of access to grain in the experimental chamber. The acquisition of the treadle-pressing response was retarded following protracted exposure to response-independent grain deliveries and the degree of this retardation was related to the complexity of the response-reinforcer contingency.     

Glucose effects on memory: behavioral and pharmacological characteristics

Recent findings indicate that post-training glucose injections can modulate memory storage for inhibitory (passive) avoidance training. Experiment I extended these findings to determine whether glucose, like other memory modulating treatments, enhances memory storage when administered after training with low footshock and impairs memory storage after high footshock training. In Experiment I, male Sprague-Dawley rats were trained in a one-trial inhibitory avoidance task using either a brief footshock (0.5 mA, 0.7 s) or slightly more intense footshock kept on until escape (0.7 mA, mean escape latency = 3.4 s). Immediately after training, each rat received a subcutaneous injection of glucose (100 mg/kg). When tested for retention performance 24 h later, the glucose-injected animals exhibited enhanced retention performance for low footshock training and impaired retention for high footshock training. Experiment II determined whether pretreatment with adrenergic antagonists blocked the effects of glucose on memory. Pretreatment with the alpha- or beta-adrenergic receptor antagonists, phenoxybenzamine, or propranolol, respectively, had no effect on acquisition or retention in animals trained with the brief footshock and did not affect glucose facilitation of that memory. In animals trained to escape footshock, phenoxybenzamine did not attenuate the amnesia produced by glucose. Propranolol-pretreated animals had impaired retention whether or not they received post-training amnestic injections of glucose; glucose had no effect on retention in these amnestic animals. These findings add further support to the view that glucose release after training and treatment may represent a physiological response subsequent to epinephrine release in modulating memory storage processing.     

Presentation- and test-trial effects on acquisition and retention of distance and location

Acquisition and retention effects of presentation and test trials on movement distance (Experiment 1) and location (Experiment 2) were examined under three multitrial training methods. Three groups of 15 government employees performed three training trial cycles consisting of six trials each. Training methods emphasized either presentation-trial repetition, test-trial repetition, or presentation- and test-trial alternation within cycles. After training, both short- (3 min.) and long-term (24 hr.) retention scores were recorded. Absolute error revealed that (a) presentation-trial repetition promoted acquisition of both distance and location but resulted in extensive short- and long-term forgetting; (b) test-trial repetition produced error increases within cycles, potentiated presentation-trial effectiveness during acquisition, and enhanced long-term retention of both distance and location; (c) presentation- and test-trial alternation promoted distance and location acquisition and produced distance retention intermediate to that of the other two methods. Experiment 3 provided data to support the interpretation that test-trial retention benefits are a function of movement execution mode.     

Shock preexposure and the reduced effectiveness of shock

In three experiments experience with shock was shown to reduce the effectiveness of shock as a reinforcer or motivator. In Experiment 1 rats were given signaled shock in a box separate from the runway where they were subsequently punished. These rats were less suppressed by shock punishment than rats that had no previous shock experience. In Experiment 2 preshocked rats were less suppressed by punishment and were slower to learn an escape-avoidance response than nonpreshocked rats, whether the preshock was signaled or unsignaled. In Experiment 3 as number of CS-shock pairings increased, fear of the CS decreased as did fear of the context. These results suggest that some central adaptation process produced by experience with shock reduces the effectiveness of shock as a reinforcer whenever shock is used repeatedly. This is independent of other effects, such as context blocking, that can affect responding after shock preexposure.     

Retardation of autoshaping following pretraining with unpredictable food: Effects of changing the context between pretraining and testing

In Experiment 1, pigeons exposed to US ONLY pretraining were observed to be retarded in the acquisition of autoshaping relative to naive controls; however, gross changes in contextual stimuli between pretraining and testing alleviated the retardation effect. In Experiment 2, groups of pigeons exposed to CS ONLY, US ONLY, or random CS-US presentations (TRC) were tested for the acquisition of autoshaping. The US ONLY and TRC groups were retarded relative to naive controls. The context change manipulation eliminated the US ONLY retardation effect and attenuated, but did not eliminate, the TRC retardation effect. Context blocking accounts for the US ONLY effect and contributes to the TRC effect; however, context-independent retardation following TRC pretraining suggests the operation of the learned irrelevance cognition.     

Effect of schedule and magnitude of reinforcement on instrumental learning in the toad, Bufo arenarum

Extinction after training with continuous (CR) or 50% partial (PR) reinforcement, and with different magnitudes of reward, was studied in the amphibian Bufo arenarum, in a runway situation. In Experiment 1, a group of toads received massed-trial, CR training with access to water as the reward. Performance improved during acquisition, including an improvement on the first trial of each session. Extinction was rapid and there was evidence for spontaneous recovery of the running response. In Experiment 2, groups of toads received PR or CR training at a rate of one trial per day. PR impaired acquisition and resulted in poor responding during extinction, compared to CR. Experiment 3 factorially studied the effects of schedule (PR vs CR) and distribution of practice (15 s vs 300 s intertrial interval). Acquisition was impaired by PR training but had little effect on extinction performance. Different magnitudes of water reinforcement were used in Experiment 4 in a one-trial-per-day situation. Terminal acquisition performance was a monotonic function of reward magnitude, but there were no differences in extinction performance across groups. The results are discussed in relation to comparative and developmental data on the paradoxical effects of reward.     

Interaction of Pavlovian conditioning with a zero operant contingency: chronic exposure to signaled inescapable shock maintains learned helplessness effects

In four experiments we used triads, consisting of escapable-shock (ES), yoked inescapable-shock (IS), and no-shock (NS) rats, to investigate the effect of the interaction between Pavlovian contingencies and a zero operant contingency (i.e., uncontrollability) upon subsequent shock-escape acquisition in the shuttle box. After exposure to 50 signals and shocks per session for nine sessions, interference with shuttle box escape acquisition for IS rats was a monotonically increasing function of the percentage of signal-shock pairings during training (Experiment 1), with 50% pairings producing little or no impairment. Without regard to signaling, ES rats performed as well as NS rats. Experiment 2 demonstrated that our training and test conditions led to substantial and equal impairment in IS rats preexposed for one session to 100% or 50% signal-shock pairings or to unsignaled shocks. In Experiment 3, chronic exposure to 100% signaled inescapable shocks resulted in impairment only if the signal (light) was present during the shuttle box test. The continuous presence of the signal during the test contrasted with its discrete (5-s) presentation during training and suggested that an antagonistic physiological reaction rather than a specific competing motor response had been conditioned. Experiment 4 provided evidence for possible conditioned opioid mediation by demonstrating contemporaneous stress-induced analgesia and shock-escape impairment in IS rats chronically exposed to 100%, but not to 50%, signal-shock pairings, and the elimination of both analgesia and escape interference by the opiate antagonist naltrexone. Thus, chronic exposure to uncontrollable shocks appears to maintain the impairment produced by acute exposure only if the shocks are adequately signaled.     

MOVEMENT SUPPRESSION TIME-OUT FOR UNDESIRABLE BEHAVIOR IN PSYCHOTIC AND SEVERELY DEVELOP MENTALLY DELAYED CHILDREN

The effects of a movement suppression time-out, which involved punishing any movement or verbalization while a client is in the time-out area, were evaluated in four experiments. The first experiment examined the effects of a DRO procedure and movement suppression plus DRO in suppressing self-injurious behavior in a psychotic child in three different situations. In Experiment 2, the results of the previous experiment were replicated with two dangerous behaviors in a second psychotic child. In a third experiment, movement suppression plus DRO was compared with contingent restraint in reducing inappropriate poking behavior in two settings. The movement suppression procedure eliminated poking whereas contingent restraint had little effect. In the final experiment, movement suppression time-out alone was compared with exclusionary time-out alone and simple corner time-out alone. Self-stimulation occurred at high levels during the exclusionary and simple corner time-out procedures. Self-stimulation was either suppressed or reduced during movement suppression time-out. The movement suppression time-out procedure produced a larger reduction in the target behavior in all three children. The effectiveness of the movement suppression procedure was explained in terms of the suppression of self-stimulation while the time-out procedure was being applied.     

Pavlovian processes and response competition as determinants of avoidance response-prevention effects

Two experiments investigated the facilitation of avoidance extinction by exposure to lengthy (5-sec) shock during avoidance response prevention. In Experiment 1, animals exposed to light only or to light-shock pairings during response prevention showed equal facilitation of extinction relative to shock-only animals or to animals receiving no response prevention. Preshock rearing, directly antagonistic to the avoidance response, developed for shocked animals during response prevention and persisted during extinction for light-shock animals. Immediately before extinction, half of each group was permitted a single escape from a light-shock compound by means of the response previously required for avoidance. The only effect was upon the extinction performance of light-shock animals. Rearing was eliminated and extinction responding increased to a level far above that for any of the other animals. Experiment 2 demonstrated that the shock-only treatment affected the extinction performance and rearing of nonescape and escape animals in a manner entirely equivalent to the effects of the light-shock treatment of Experiment 1, provided stimulus conditions (light absent) were the same for all experimental phases. Thus, lengthy shock during avoidance response prevention simultaneously leads to the acquisition of competing behavior and enhances control by a warning signal or contextual stimuli over the avoidance response. Implications for the CS-only response-prevention treatment and the transfer of aversive control are discussed.     

Reduction of ontogenetic retention decrements in rats by pretraining stressful experiences.

Pretraining stressful experiences, either similar to or qualitatively different from the conditioning unconditioned stimulus, reduced ontogenetic retention decrements without directly influencing response acquisition. Rats that received pretreatment with footshock, hypthermia, or restraint on Days 16, 17, and 18 of age showed substantially improved long-term retention of conditioned fear learned at 20 days of age. It was also found that preshock enhanced retention of both an appetitive approach response and punishment of the approach response. Several experiments involving extinction and undertraining manipulations indicated that the facilitation of retention was not directly attributable to acquisition strength.     

Loss of associability by a compound stimulus comprising excitatory and inhibitory elements

In each of two experiments rats learned a discrimination between a stimulus (A) that signaled shock and a compound stimulus (AB) that signaled no shock. In Experiment 1 it was found that the AB compound acquired excitatory strength only slowly when, in a second phase of training, it was made to signal the occurrence of shock. In Experiment 2 the acquisition of inhibitory strength by the compound was similarly found to be retarded. This second experiment also replicated the results of Experiment 1. The relevance of these results to current theories of latent inhibition and attention is discussed.     

Partial reinforcement effects in instrumental escape conditioning

In Experiment I acquisition and extinction of instrumental escape conditioning with rats (N = 64) were studied as a function of reinforcement magnitude under conditions of partial and continuous reinforcement. In Experiment II the effects of partial and continuous reinforcement were studied in rats (N = 96) during acquisition followed by small, medium, and large reductions in reinforcement magnitude. A water-tank escape apparatus was used with temperature as the relevant variable. It was found that (1) with large reinforcement magnitude a continuously reinforced group was superior in acquisition to one that was partially reinforced; there were no differences with small reinforcement; (2) disruptive effects of a nonreinforced trial (a) appear early in learning, (b) are quite strong after each nonreinforced trial, and (c) persist through several succeeding reinforced trials; (3) major competing behaviors persist throughout acquisition for small reinforcement magnitude regardless of schedule, decline with large reinforcement (more so with continuous than with partial), and return to a high level in extinction for all conditions; (4) the partial reinforcement extinction effect occurs after large reinforcement but not after small, and it appears only with large reductions in reinforcement magnitude which approach extinction conditions. Only the first part of the last finding appears to be consistent with the appetitive conditioning literature.     

Effects of glucose on scopolamine-induced learning deficits in rats performing the Morris water maze task

In order to assess the effects of glucose on drug-induced spatial learning deficits, three experiments were conducted using the Morris water maze. Scopolamine and glucose were injected ip at various stages of training. Rats of Wistar strain served as subjects. In Experiment 1, scopolamine (0.4 mg/kg) and 10, 100, or 500 mg/kg of glucose were administered every day from the start of training, and the effect on acquisition was evaluated. In Experiment 2, scopolamine and 100 or 500 mg/kg of glucose were administered after 6 days of training, and the effect on performance was assessed. In Experiment 3, scopolamine and 500 mg/kg of glucose were injected after 2 days of training, and the effect on the following trial was tested. In all experiments, scopolamine impaired acquisition/performance of the task. Glucose at 500 mg/kg showed a significant enhancing effect on acquisition regardless of scopolamine injection only when injected daily from the start of training (Experiment 1). Glucose injected after the performance has reached asymptote (Experiment 2) did not affect performance, and glucose in the middle of training showed a slight but insignificant enhancing effect (Experiment 3). These results may suggest that the effect of glucose changes as a function of the degree of learning of the spatial learning task. The possibility of task specificity of the glucose effect was also discussed in relation to the cholinergic systems and local cerebral glucose utilization.