Actual versus potential shock in making shock situations function as negative reinforcers

The relative importance of potential and actual shocks in making shock situations function as negative reinforcers was studied. Shocks were scheduled to occur at the same rate during two stimuli. During one, squirrel monkeys could avoid the shocks; during the other, they were unavoidable. For the two stimuli the potential rate of shocks was the same, but the actual rate was lower during avoidance because of avoidance responding. Fixed-ratio responding was maintained by the change from unavoidable shock to avoidance, indicating that the change was reinforcing when it resulted in a reduction in actual shock rate with no reduction in potential shock rate. Further increases in the rate of potential shock during avoidance had little effect upon the fixed-ratio responding until the rate was increased to the point that the actual shock rate during avoidance was comparable with that during unavoidable shock. At that point, the fixed-ratio response rate decreased nearly to zero. These findings show that actual shocks are more important than potential shocks in determining whether or not a shock situation will function as a negative reinforcer; this explains why the change from unavoidable shock to avoidable shock is reinforcing.     

Risk factors of suicidal ideations and attempts in talented, at-risk girls

The purpose of the present study was to investigate the relationships among suicidality, substance use, self-esteem, family structure, and eight personality characteristics (harm avoidance, impulsivity, aggression, social recognition, cognitive structure, succorance, abasement, and achievement) with 337 talented, at-risk, adolescent girls. Results indicated that girls with histories of suicidal ideations and/or attempts had significantly higher levels of substance use, impulsivity, aggression, and social recognition, and significantly lower levels of self-esteem and harm avoidance than girls without such histories. Girls without suicide histories were also more likely to come from single mother families. Consideration of these factors, by both researchers and clinicians, in assessing suicide risk is encouraged.     

Avoidance extinction in goldfish

Independent groups of goldfish trained to avoid shock in a shuttlebox situation were presented with several extinction procedures in which the relationships between the conditioned stimulus and shock were altered and/or response contingencies removed. Random shock presentations, equivalent to the number of shocks received during avoidance acquisition, resulted in response decrements similar to those obtained when the conditioned stimulus was presented alone. Pairing the conditioned stimulus with shock on every trial, however, served to maintain response levels. When response-contingent punishment was superimposed upon these Pavlovian pairings, performance was facilitated slightly although punishment alone resulted in somewhat faster response reduction than that produced by exposure only to the conditioned stimulus. Extinction of avoidance responding produced by exposure to the conditioned stimulus alone was dependent on the total duration of exposure and independent of both number of stimulus onsets and response prevention. These experiments demonstrated that, in general, the procedures used to reduce avoidance responding in rats were equally effective for goldfish, with one exception: the introduction of a Pavlovian contingency following avoidance acquisition, making the previously avoidable shock unavoidable, maintained response probabilities near previously established levels.     

Lever attacking and pressing as a function of conditioning and extinguishing a lever-press avoidance response in rats

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.     

Running-wheel activity and avoidance in the mongolian gerbil

In the first of two experiments, running-wheel activity and unsignaled (Sidman) avoidance were studied in gerbils and albino rats. All gerbils ran at higher rates than any of the four rats studied. Under the avoidance procedure, four rats developed effective responding; the other two performed much less successfully. While avoidance developed more slowly in the gerbils, all showed asymptotic performance as effective as the four superior rats. The rats showed a consistent warm-up effect, receiving 60% to 80% of the total shocks in the initial third of the session. The gerbils displayed no warm-up, with shocks being evenly distributed over the session. Warm-up in the rats was not related to either response rate or to how effectively the animal was avoiding. When shock was removed, extinction occurred more rapidly in the rats than the gerbils. In the second experiment, which involved two-way shuttle avoidance, gerbils and albino mice quickly acquired the response. All animals met a criterion of 90% avoidance over 80 trials.     

Immobility as an avoidance response, and its disruption by drugs

Much of the available literature on avoidance behavior is based on responses which require the animal to run, lever-press, or to make some active response to avoid noxious stimulation. The purpose of Experiment I reported in this paper was to determine whether animals can learn to sit or stand motionless in order to escape or avoid electric shock. Five experimental rats were given escape-avoidance training, while five yoked control animals received electric shocks without any response-related contingency. It was shown that an immobility avoidance response, as distinct from the unconditioned “freezing” response to shock, can be trained. The results of Experiment II (30 rats) revealed that this response is more readily acquired at higher shock intensities than at lower ones, provided escape by jumping is prevented at the high shock intensities. The effects of six doses of each of three drugs on the immobility avoidance response were studied in Experiment III (13 rats). Methylphenidate, chlorpromazine, and imipramine all produced a decrement in the immobility response, but the pattern and amount of the effects of the three drugs were quite different, one from the other. The implications of these findings for a general theory of avoidance behavior and for drug screening are discussed.     

Conditional fear,anxiety, and morphine-seeking behavior

TwoCebus albifrons monkeys were given discriminative operant conditioning with visual stimuli, with Sidman avoidance and punishment as the components. The instrumental response was an unelicited increase in skin conductance. Both animals had surgically implanted catheters for automatic injection of morphine into the heart. After autonomic conditioning, the animals were given the opportunity to self-administer the morphine by touching the primate press panel that displayed the visual stimuli. One contingency-free segment per session was used for morphine injection, while the contingencies remained in force during the other segments. One of the monkeys made significantly more skin conductance responses during avoidance than during punishment, and this monkey received ten times as many shocks in punishment. This monkey also made more responses overall and had a much higher heart rate than the other animal. The other monkey did not differentiate significantly autonomically and received equal numbers of shocks in avoidance and punishment. The monkey that showed autonomic differentiation made significantly (and increasingly) more panel-presses during punishment than during avoidance. The other animal showed hardly any tendency at all to panel-press.     

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.     

Persistent behavior maintained by unavoidable shocks

Squirrel monkeys were trained on a multiple schedule in which 10-min periods on a continuous shock avoidance schedule, indicated by a yellow light, alternated with 10-min periods on a 1.5-min variable interval schedule of food reinforcement (VI 1.5). A white light indicated that VI 1.5 was in effect, except for the middle 2 min of the period on VI 1.5, in which a blue light appeared and terminated with the delivery of a 0.5-sec unavoidable shock. Stable response rates developed in the avoidance and VI 1.5 components. However, the highest response rates occurred in the blue, preshock stimulus. A series of experiments showed that responding in the blue stimulus persisted even when responding had been extinguished on both the VI schedule of food reinforcement and the shock avoidance schedule. Responding in the blue stimulus ceased when the blue stimulus terminated without shock or when it terminated with a response-contingent shock. Each time responding ceased, it was restored by terminating the blue stimulus with an unavoidable shock. When the blue stimulus was on throughout each session and unavoidable shocks were delivered at regular 10-min intervals, responding was well maintained. These results show that in monkeys that have been trained on a continuous avoidance schedule, unavoidable shocks can maintain responding even under conditions where responses have no programmed consequences.     

Fighting,nonagonistic social behavior,and exploration in isolation‐reared rats

Sixty hooded Long‐Evans rats were assigned to one of three conditions: isolation‐rearing (from 14–30 days of age), brief isolation (from 28–30 days of age), and normal (no isolation). From day 14 to day 21, the isolation‐reared animals were maintained in an incubator set at 35°C to prevent hypothermia and were separated from each other by Plexiglas. They learned to nourish themselves by lapping milk that continuously flowed down one side of the enclosure. Thereafter, they were housed in standard hanging wire cages. Unlike previous studies of isolation at this age, there were no significant weight differences between the isolation‐reared group and the two control groups. At 30 days of age, the three groups were compared on fighting (serious and play), nonagonistic social behaviors (following and crawling under), and exploratory behavior (open‐field ambulation). The isolation‐reared group was significantly different from the normal group on all measures (isolates were higher on all measures except exploration). The isolation‐reared animals showed significantly more serious fighting (aggression) than the brief isolation animals, whereas these two groups did not differ on other behaviors. This methodology allows for the study of isolation‐rearing without the nutritional confounds found in previous research and shows an effect on aggression that is not accounted for by recent isolation. Aggr. Behav. 25:211–223, 1999. © 1999 Wiley‐Liss, Inc.     

Sex,strain, and housing: Variables influencing the effects of prior shock exposure on shock-induced aggression

A series of experiments was conducted to investigate sex, housing conditions, and strain as possible factors influencing the interference effect of prior exposure to shock on shock-induced aggression. In albino subjects, female rats and rats housed in community cages evidenced the greatest suppression in aggression following prior exposure to shock. In addition, ten sessions of prior exposure to shock produced a greater suppression in shock-induced fighting than 20 sessions of prior exposure to shock. The prior shock effect was not obtained with hooded subjects. Responsivity to shock was also investigated to determine whether the prior exposure to shock attenuation of shock-induced fighting was a consequence of reduced activity in response to shock. Responsivity to shock measured with an isometric platform accounted for less than 4% of the variance in shock-induced fighting in the single experiment that obtained a correlation between responsivity and shock-induced aggression.     

The ventromedial hypothalamus and aggressive behaviour in rats

Male rats were given bilateral lesions in either the anterior or posterior ventromedial hypothalamus (VMH). The intermale aggressive behaviour of these animals within their own territory was observed before and after the surgical procedure and compared with the behaviour of sham-operated animals. The effects of anterior VMH lesions include an increased tendency to respond with frontal threatening upon approach of a conspecific male. This behaviour closely resembles the aggressive responses described in “shock-induced aggression” tests. Posterior VMH lesions facilitate territorial aggressive behaviour characterized by approaching the opponent followed by lateral threatening and fighting. It is suggested that 2 distinct neural substrates exist, which serve to inhibit defensive (anterior-VMH) and offensive (posterior-VMH) intermale aggression, respectively.     

Effects of previous housing conditions on shock-induced aggression.

This study investigated shock-induced aggression as a function of housing rats in single or communal cages for varying periods of time before testing. Rates of fighting were unaffected by housing conditions when rats spent seven or 14 days in either of these settings before testing. Placing rats in these settings for 21 or 28 days before testing, however, did affect rates of fighting. Communal caging of subjects for 28 days before testing was particularly deleterious to shock-induced aggression. How rats are housed outside the experimental chamber is a variable affecting shock-induced aggression and should be considered both in designing future studies and as a topic for future investigation.     

Continuous punishment of free-operant avoidance in the rat

Three groups of albino rats were trained under a free-operant avoidance (Sidman) procedure with equal shock-shock and response-shock intervals. After stable performance was achieved, the animals were concurrently exposed to a brief electric shock after each response. The procedures were as follows: Punishment Schedule I: punishment shock was introduced at an intensity approximately one quarter that of avoidance shock; increments of nearly this same size were made as stable performance was achieved at succeeding punishment shock intensities. Punishment Schedule II: punishment shock was introduced at approximately one-half the intensity of avoidance shock; after stable performance, punishment shock was increased to the same intensity as avoidance shock. Punishment Schedule III: punishment shock was introduced and maintained at the same intensity as avoidance shock. Punishment was continued for all groups until one of two suppression criteria was attained. All animals made fewer responses and received more avoidance shocks as a function of increasing punishment shock. Half of the animals under Punishment Schedule I required punishment shock higher than avoidance shock to meet their assigned suppression criterion. A comparison of all procedures showed that suppression was greater when punishment shock was initially at high intensity.     

Effects of age at differential housing and the duration of individual housing/grouping on lntermale fighting behavior and adrenocortical activity in TO strain mice

A study of the effects of the duration of individual and group housing on intermale fighting and adrenocortical activity was conducted in TO strain mice. It was found that fighting and threat increased with progressive isolation up to an asymptote at 56–58 days. ‘Basal’ adrenocortical function differed little under the 2 housing conditions, but after ‘stress,’ mice isolated for short periods, which had not fought when tested for aggression, had lower titers than group-housed counterparts. However, mice that had been isolated for longer periods, and had fought in aggression tests, had higher corticosterone titers than comparable group-housed animals. The effects of a short duration (28–30 days) of differential housing, commencing at different ages, were also studied. The shorter duration adrenocortical changes were largely confirmed. In general, the earlier the age at which the differential housing was imposed, the greater the behavioral differences between animals under each housing condition. It is suggested that this is largely a consequence of a loss of behavioral plasticity in older mice. The data provides little support for the concept of the “isolation stress syndrome,” or for the view that the characteristic fighting exhibited by individually housed mice is a consequence of “social deprivation”.     

Behavioral studies in spontaneously hypertensive rats

In the present study we examined some behavioral patterns in spontaneously hypertensive (SHR) male rats as compared with Wistar (W) rats. The following methods were employed: open field test, two-way active avoidance, passive avoidance, shock-induced fighting, shock-induced suppression of drinking (conflict test), and dominant-subordinate behavior in rats competing for water. Spontaneously hypertensive rats showed higher level of locomotor activity, lower emotionality, lower anxiety level, increased acquisition of avoidance tasks, and enhanced dominance behavior. In addition, hypertensive rats were less aggressive in shock-induced fighting test. It is concluded, that spontaneously hypertensive rats seem to be hyperactive in terms of locomotor activity while their emotionality appears to be paradoxically reduced.     

MODIFICATION OF SHUTTLE BOX TO IMPROVE RATE OF AVOIDANCE LEARNING IN RATS

W allgren , H. & S avolainen , S. Modification of shuttle-box to improve rate of avoidance learning in rats. Scand. J. Psychol ., 1962, 3 , 78–80.—Acquisition by rats of a conditioned avoidance response seems to be retarded in an ordinary shuttle-box by the necessity to re-enter the compartment where shocks have previously been received. To avoid this, a four-compartment box was introduced in which the animals can proceed in one direction. Rats were given either continuous trials until nine avoidance responses were made during 10 consecutive trials, or 30 trials per day until 27 correct responses were made during one session. With both methods of training, the rate of learning was approximately 40 per cent more rapid in the four-compartment box than in the ordinary shuttle-box.     

Some effects of response-independent shocks after unsignaled avoidance conditioning in rats

After extended unsignaled avoidance training, the majority of rats continued frequent responding during long periods when only response-independent shocks were presented. Most responses were shock elicited, i.e., followed immediately after shock. Response rates were directly related to both the frequency and the intensity of response-independent shocks. Responding continued to approximately the same extent, whether shocks were presented at fixed or variable intervals. Few responses were directed toward a second lever in the test chamber, even when the lever previously associated with avoidance was removed. When avoidance was scheduled on the second lever, the rats learned to avoid by operating it. Meanwhile, responding on the first lever became infrequent. Subsequently, when only response-independent shocks were presented, almost all responses occurred upon the lever initially associated with avoidance. Responding that was elicited by response-independent shocks was suppressed by response-dependent (punishment)_shocks of the same intensity. When punishment was withdrawn, recovery of responding occurred. An explanation of the results based upon shock-elicited behaviors is preferred to one stressing unextinguished avoidance responding.     

Reduction of shock duration as negative reinforcement in free-operant avoidance

Rats were trained on a free-operant procedure in which shock duration was controlled by responses within a limited range of interresponse times. Shocks of 1.6-mA intensity occurred randomly with average density of 10 shocks per minute. As long as interresponse times were 15 seconds or less, any shocks received were at the briefer of two durations (.3 second). Whenever interresponse times exceeded 15 seconds, any shocks received were at the longer duration (1.0 second). For six of eight animals, avoidance responding developed quickly and reached levels of better than 90%. Four yoked animals stopped responding within the first few sessions. Shock duration reduction without change in shock probability or intensity was sufficient for the acquisition and maintenance of avoidance responding.     

Avoidance based on shock intensity reduction with no change in shock probability

Rats were trained on a free-operant avoidance procedure in which shock intensity was controlled by interresponse time. Shocks were random at a density of about 10 shocks per minute. Shock probability was response independent. As long as interresponse times remained less than the limit in effect, any shocks received were at the lower of two intensities (0.75 mA). Whenever interresponse times exceeded the limit, any shocks received were at the higher intensity (1.6 mA). The initial limit of 15 seconds was decreased in 3-second steps to either 6 or 3 seconds. All animals lever pressed to avoid higher intensity shock. As the interresponse time limit was reduced, the response rate during the lower intensity shock and the proportion of brief interresponse times increased. Substantial warmup effects were evident, particularly at the shorter interresponse-time limits. Shock intensity reduction without change in shock probability was effective in the acquisition and maintenance of avoidance responding, as well as in differentiation of interresponse times. This research suggests limitations on the generality of a safety signal interpretation of avoidance conditioning.