Schedule Of Shock Presentation Research Articles

Effects of ethanol on punished and nonpunished responding under conditions of equated reinforcement rates and similar response rates

Lever pressing by pairs of rats was maintained under random-ratio (first subject) and yoked-interval (second subject) schedules of food presentation. The inter-reinforcement intervals generated under the ratio schedule comprised the interval values for the second (yoked) subject. This arrangement yielded nearly equivalent rates of food presentation for each subject pair. For the first rat of each pair a random-ratio schedule of shock presentation was added to the ratio schedule of food presentation. This manipulation resulted in similar rates of punished (first rat) and nonpunished (second rat) responding within subject pairs. Ethanol administration (0.25–1.5 g/kg) generally resulted in dose-related decreases in both punished and nonpunished responding. In general, punishment-specific effects were not obtained. These results suggest that ethanol may not be as effective as chlordiazepoxide or pentobarbital in increasing punished responding even when the effects of baseline response and reinforcement rates are controlled.

Acute administration of diazepam and buspirone in rats trained on conflict schedules having different degrees of predictability

The anti-conflict activities of diazepam and buspirone were examined on three schedules designed to condition the suppression of licking. The schedules differed in the degree to which they predicted (signalled) the presentation of a conflict inducing electric shock. The first study investigated the effects of three doses of diazepam (0.5, 2, and 5 mg/kg IP) on a predictable, a moderately predictable, and an unpredictable schedule of shock presentation. Diazepam induced a significant increase from baseline in licking during the shock component on all three schedules. These anticonflict effects were the most consistent on the predictable schedule, and least consistent on the unpredictable schedule. A second experiment investigated the anticonflict activity of three doses of buspirone (0.125, 0.25, and 0.625 mg/kg SC) on each of these three schedules. The predictable and moderately predictable schedules failed to detect anticonflict activity at any dose of buspirone. However, the lowest dose (0.125 mg/kg) of buspirone increased shocked licking and the highest dose (0.625 mg/kg) decreased shock component licking on the unpredictable schedule. Thus the unpredictable schedule was sensitive to both anticonflict (anxiolytic) and proconflict (anxiogenic) effects of buspirone.

The effects of acute administration of gepirone in rats trained on conflict schedules having different degrees of predictability

The anticonflict activity of gepirone, a putative anxiolytic and antidepressant, was examined on three schedules which conditioned the suppression of licking. The novel schedules differed in the degree to which they predicted (signalled) the presentation of a conflict-inducing electric shock. Three doses of gepirone (1.25, 2.5, and 5 mg/kg SC) were evaluated on a predictable, a moderately predictable, and an unpredictable schedule of shock presentation. Gepirone induced a nondose-dependent increase from baseline in punished licking on the predictable schedule on the last two days of a five-day test period. The lowest dose (1.25 mg/kg) of gepirone induced a significant increase in punished licking on the moderately predictable schedule on the last two days of testing. The highest dose (5 mg/kg) induced initial decreases in overall responding on this schedule. However, responding returned to baseline over the course of the four days of testing. When administered to rats trained on an unpredictable schedule of shock presentation, all doses of gepirone induced an initial decrease from baseline. The lowest dose group returned to baseline control response levels over the next four days, whereas the suppressive effects of the higher doses persisted. The initial decrease in responding observed on all schedules may be due to the effects of gepirone on motor functioning. However, the 2.5-mg/kg dose induced a proconflict or anxiogenic effect on the last test day (decreased punished responding alone) on the unpredictable schedule, while inducing an anticonflict effect on the predictable one. The unpredictable schedule is sensitive to detecting decreases as well as increases in punished responding and as such may be a unique conflict model for evaluating novel anxiolytics.(ABSTRACT TRUNCATED AT 250 WORDS)

Can animal models really predict anxiety?

The anti-conflict activities of diazepam and buspirone were examined on three schedules designed to condition the suppression of licking. The schedules differed in the degree to which they predicted (signalled) the presentation of a conflict inducing electric shock. The first study investigated the effects of three doses of diazepam (0.5, 2, and 5 mg/kg IP) on a predictable, a moderately predictable, and an unpredictable schedule of shock presentation. Diazepam induced a significant increase from baseline in licking during the shock component on all three schedules. These anticonflict effects were the most consistent on the predictable schedule, and least consistent on the unpredictable schedule. A second experiment investigated the anticonflict activity of three doses of buspirone (0.125, 0.25, and 0.625 mg/kg SC) on each of these three schedules. The predictable and moderately predictable schedules failed to detect anticonflict activity at any dose of buspirone. However, the lowest dose (0.125 mg/kg) of buspirone increased shocked licking and the highest dose (0.625 mg/kg) decreased shock component licking on the unpredictable schedule. Thus the unpredictable schedule was sensitive to both anticonflict (anxiolytic) and proconflict (anxiogenic) effects of buspirone.

SELECTIVE PUNISHMENT OF INTERRESPONSE TIMES: THE ROLES OF SHOCK INTENSITY AND SCHEDULING

Two experiments investigated the roles of shock intensity and scheduling in selective punishment of interresponse times. In each experiment the punishment contingencies were imposed on a background of rats' responding maintained by a variable-interval schedule of food presentation. In Experiment 1 all interresponse times greater than 8 seconds produced shock. In Experiment 2 all interresponse times greater than 8 seconds but less than 12 seconds produced shock. In each experiment shock intensity was initially 0.3 milliamperes (mA) and then was varied through an ascending sequence ranging from 0.1 mA to 0.4 mA, in 0.1-mA increments. Experiment 1 produced response-rate increases at low intensities (0.1 and 0.2 mA) but eliminated responding at the remaining intensities. Experiment 2 produced response-rate increases only with 0.1-mA shock, although responding was maintained at all shock parameters investigated. Analysis of the interresponse times per opportunity showed differential suppression of the targeted responses in all cases except the high-intensity shock phases of Experiment 1. The current data support and extend previous studies of selective interresponse-time-dependent shock schedules but suggest that response-rate increases are not a necessary outcome of this type of procedure. The view that variable-interval schedules of shock presentation selectively target long interresponse times was also supported.

Interresponse-time punishment: a basis for shock-maintained behavior.

Lever pressing of squirrel monkeys postponed brief electric shock according to a free-operant shock-postponement procedure. Pressing also produced shock with a probability proportional to the duration of the current interresponse time in some conditions, or to the fifth ordinally-preceding interresponse time in others. These conditions provided equal frequencies and temporal distributions of response-produced shocks either contingent on or independent of the current interresponse-time duration, respectively. Shock delivered contingent on the current interresponse-time duration resulted in shorter mean interresponse times and higher overall response rates that shock delivered independent of the current interresponse time. In subsequent conditions, response-produced shocks were sufficient to maintain responding following suspension of the postponement procedure only when those shocks were contingent on the current interresponse time. Presenting shock independent of the current interresponse time, conversely, suppressed response rate and ultimately led to cessation of responding in the absence of a conjoint shock-postponement procedure. These results demonstrate interresponse-time punishment in the absence of any indirect avoidance contingencies based on overall shock-frequency reduction, and strongly support similar interpretation at the more local level of shock-frequency reduction correlated with particular interresponse times. Differential punishment of long interresponse times also provides both an a priori basis for predicting whether a schedule of shock presentation will maintain or suppress responding and a framework for interpreting many of the functional relations between overall response rate and parameters of consequent shock presentation. Finally, these results and others indicate the importance of response-consequence contiguity above and beyong any notion of noncontiguous contingency in the control of behavior.

Evidence against the involvement of serotonergic neurons in the anti-punishment activity of diazepam in the rat.

The effects of manipulating central serotonergic transmission were assessed on the anti-punishment effects of diazepam (2 mg/kg IP) in rats. In a paradigm involving the inhibition of pressing for food induced by the delivery of a signal previously associated with electric foot-shocks, lesioning serotonergic neurons of the dorsal raphé with the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT; 1 microgram in 0.4 microliter) neither affected behavioral inhibition in control rats nor modified the ability of diazepam to release responding. Furthermore, suppression of pressing for food induced by a fixed ratio 7 schedule of shock presentation was reduced by bilateral infusion of 5,7-DHT (2 micrograms in 0.5 microliter) into the substantia nigra, but the ability of diazepam to increase punished responding was preserved. Finally, blockade of benzodiazepine-induced decrease in serotonin release by application of the benzodiazepine receptor antagonist Ro 15-1788 (10(-5)-10(-4)M in 0.2 microliter) into the dorsal raphé did not alter the releasing effect of diazepam on suppression of pressing for food caused by a signal of punishment. At these concentrations. Ro 15-1788 was devoid of any effect on behavioral inhibition in control rats. Taken together, these results indicate that the anti-punishment activity of benzodiazepines can be dissociated from the reduction in tryptaminergic transmission produced by these drugs.

RESPONDING MAINTAINED UNDER INTERMITTENT SCHEDULES OF ELECTRIC‐SHOCK PRESENTATION: “SAFETY” OR SCHEDULE EFFCTS?

Four experiments were conducted in which lever pressing by squirrel monkeys was maintained under multiple, mixed, or chained schedules of electric-shock presentation. In the first two experiments, a multiple schedule was employed in which a fixed-interval schedule of shock presentation alternated with a signaled two-minute component. Initially, no events were scheduled during the two-minute component (a safety period). In the first experiment, the safety period was "degraded" by introducing and systematically increasing the frequency of periodic shocks presented during that component. In the second experiment, the proportion of overall safe time to unsafe time was decreased by decreasing the value of the fixed-interval schedule while holding constant shock frequency during the two-minute component. In the third experiment, the overall arrangement was changed from a multiple to a mixed schedule in an attempt to determine whether fixed-interval responding would be maintained when a single exteroceptive stimulus was associated with both components. In the fourth experiment, the overall arrangement was changed from a multiple to a chained schedule in an effort to determine whether fixed-interval responding would be maintained when its consequence was presentation of a signaled "unsafe" period. Fixed-interval responding was well maintained under all experimental conditions; the varied relationships obtained lend more support to conceptualizations of shock-maintained behavior as exemplifying schedule-controlled behavior than to suggestions that such behavior may be readily accounted for by "safety theory."

EFFECTS OF RATIO CONTINGENCIES ON RESPONDING MAINTAINED BY SCHEDULES OF ELECTRIC‐SHOCK PRESENTATION (RESPONSE‐PRODUCED SHOCK)

Squirrel monkeys' lever pressing was established under fixed-interval schedules of electric-shock presentation (response-produced shock). After appropriate temporal patterns of lever pressing were engendered, either fixed-ratio schedules of shock presentation were added to the fixed interval, or yoked variable-ratio schedules were substituted for the fixed-interval schedules. When fixed-ratio schedules were added, there was an initial rise in response rate and schedule-appropriate patterns of responding developed. After many sessions, however, responding ceased abruptly, in some cases with remarkable quickness. When variable-ratio schedules were substituted, responded declined gradually and eventually was poorly maintained. Ratio contingencies may not support responding as well as interval contingencies when electric shock is the maintaining event.

Clozapine effects on responding maintained under shock presentation and shock termination schedules

Clozapine, a novel antipsychotic, was studied in different squirrel monkeys responding under a 3-min fixed-interval schedule of stimulus-shock termination and a multiple 5-min fixed-interval schedule of shock presentation, 5-min fixed-interval schedule of stimulus-shock termination. Some doses (0.1–1.0 mg/kg IM) of clozapine increased responding under each fixed-interval schedule, whereas higher doses (3.0 and 5.6 mg/kg IM) usually decreased responding under each schedule. Lower response rates maintained under the stimulus-shock termination schedule were increased relatively more by clozapine than were higher rates of responding maintained under the fixed-interval schedule of shock-presentation. The present results illustrate that the effects of clozapine on schedule-controlled behaviors of squirrel monkeys differ from those of other antipsychotics.

RESPONDING UNDER SEQUENCE SCHEDULES OF ELECTRIC SHOCK PRESENTATION

Lever pressing by squirrel monkeys was examined under second-order schedules of electric shock presentation in which different discriminative stimuli were associated with consecutive components (sequence schedules). Components were always two-minute fixed-interval schedules, and three different overall schedules were studied. Under an overall eight-minute fixed-interval schedule, the first component completion after at least eight minutes had elapsed produced electric shock. The number of components actually completed ranged from one to four; thus, different discriminative stimuli were occasionally associated with electric shock presentation. Under an overall "yoked" variable-ratio schedule, electric shock was presented after completion of a variable number of components; the required number and the distribution of components were matched to those obtained under the overall eight-minute fixed-interval schedule. Under an overall fixed-ratio schedule, electric shock was presented after completion of four components (chained schedule). Under all three sequence schedules, responding in early components was characterized by a pause followed by a single response after the end of the two-minute interval; responding in later components was characterized by a shorter pause followed by positively accelerated responding. Manipulation of overall schedules of shock presentation in these complex behavioral situations produced changes in responding comparable to those ordinarily obtained after similar manipulation of dependencies under both single and second-order schedules of food presentation. These experiments extend the range of conditions and levels of complexity under which responding can be maintained by presentation of electric shock.

Responding under a Constant-Probability Schedule of Electric Shock Presentation

In squirrel monkeys responding under a continuous avoidance schedule, addition of a 3-min. constant-probability variable-interval schedule of response-produced shock (concurrent avoidance 3-min. VI) increased responding. When the avoidance schedule was eliminated, so that the only consequence of responding was the presentation of response-dependent shock under the VI schedule, characteristic VI patterns of responding were maintained. In other monkeys already responding under a 3-min. VI schedule without the constant-probability feature, characteristic patterns of responding were also maintained under the constant-probability schedule. Schedule-appropriate performances are maintained under VI schedules of shock presentation in which there is little relation between probability that a given response will be shocked and the time that has passed since the last shock, i.e., a constant-probability schedule. Substantial shock-free periods just after shock are not necessary for responding to be engendered and maintained under schedules of shock presentation.

Methamphetamine effects on responding under a multiple schedule of shock presentation

Squirrel monkeys responded under a multiple 3-min variable-interval (VI) 10-response fixed-ratio (FR) schedule of response-dependent electric shock presentation. Methamphetamine (0.01-0.17 mg/kg) produced dose-dependent increases in relatively low rates of responding whether these occurred during the FR or the VI component of the schedule. In the one monkey with a relatively high control rate of responding during the VI component, methamphetamine only produced decreases in responding. Responding during the FR component was increased by methamphetamine, even in the monkey whose responding appeared to be suppressed during this component. Previous experiments have shown only further decreases after amphetamines in responding suppressed by response-dependent shock. The present experiments indicate that, in addition to the frequency and intensity of the electric shock and to the schedule maintaining the reference behavior, the nature of the event maintaining the reference behavior can be important in determining the effects of amphetamines. The effects of methamphetamine depend not only on the intensive and temporal characteristics of the ongoing schedule-controlled behavior itself, but also on the past and present context in which the behavior occurs.

MAINTENANCE AND SUPPRESSION OF RESPONDING UNDER SCHEDULES OF ELECTRIC SHOCK PRESENTATION1

In squirrel monkeys previously trained under a continuous avoidance schedule, characteristic patterns of responding were maintained under a 3-min variable-interval schedule of shock presentation (response-produced shock). Responding in the presence of a periodically presented stimulus, the termination of which coincided with the delivery of a response-independent electric shock (Estes-Skinner procedure), was not reliably affected. When shocks followed every response during certain signalled portions of the session, and were presented under the variable-interval schedule during the rest of the session (multiple 1-response fixed-ratio, 3-min variable-interval schedule of shock presentation), responding was suppressed during the fixed-ratio component and maintained during the variable-interval component. Environmental consequences do not have immutable properties, and may either support or suppress behavior, depending on the schedule of presentation.

Varied shock and simple escape.

5 groups of rats were trained on an operant escape task under high, intermediate, or low shock conditions. Each of 3 groups received one of these intensities on all days and trials. The fourth group alternated between high and low shock intensities on consecutive days and the fifth group between high and low shock intensities randomly on consecutive trials within a day. High-intensity shock elicited faster escape responding than did low-intensity shock. Responding at a given shock level was similar regardless of the schedule of shock presentation (i.e., constant, alternated, or random). It was concluded that drive level on a given trial was the major determinant of performance.

RESPONDING UNDER FIXED‐RATIO AND MULTIPLE FIXED‐INTERVAL FIXED‐RATIO SCHEDULES OF ELECTRIC SHOCK PRESENTATION1

Squirrel monkeys, initially trained under a schedule of electric shock postponement and then under fixed-interval schedules of electric shock presentation, were studied under multiple fixed-interval fixed-ratio and under fixed-ratio schedules of shock presentation. Under the fixed-interval (10-min) component of the multiple schedule, a pause was followed by a gradual increase in responding to a rate maintained until shock presentation; under the fixed-ratio (3-, 10-, or 30-response) component of the multiple schedule, a brief pause was typically followed by a relatively high and uniform rate of responding until shock was presented. When the 60-sec timeout periods, which usually followed shock presentation, were eliminated from the multiple schedule for one monkey, responding was only transiently affected. In the one monkey studied, responding was maintained under a fixed-ratio schedule alone (with timeout periods), but rates of responding were lower than under the fixed-ratio component of the multiple schedule. Characteristic patterns of responding, similar to those engendered under schedules of food presentation or shock termination, can be maintained under fixed-ratio schedules of shock presentation; further, patterns of responding can be controlled by discriminative stimuli in multiple schedules.

SCHEDULES USING NOXIOUS STIMULI. VI: AN INTERLOCKING SHOCK‐POSTPONEMENT SCHEDULE IN THE SQUIRREL MONKEY1

Responding was studied under various schedules of electric shock postponement and presentatation in the squirrel monkey. Under an interlocking shock-postponement schedule, successive responses decreased the time by which a response postponed the next scheduled shock until a shock immediately followed the nth response. Some parameters of this schedule, which can be formally related to fixed-interval schedules, engendered a pattern of positively accelerated responding between shocks. This pattern did not occur under comparable parameter values of an alternative fixed-ratio, avoidance schedule under which each response postponed shock by a fixed duration and every nth response produced shock. Subsequently, performances were studied under schedules of shock presentation. Responding was never maintained under fixed-ratio schedules of shock presentation, but was maintained with a pattern of positive acceleration under an alternative fixed-ratio, fixed-interval schedule and under a fixed-interval schedule.

SCHEDULES USING NOXIOUS STIMULI. III. RESPONDING MAINTAINED WITH RESPONSE‐PRODUCED ELECTRIC SHOCKS1

Responding was maintained in two squirrel monkeys under several variations of a 10-min fixed-interval schedule of electric shock presentation. The monkeys were first trained under a 2-min variable-interval schedule of food presentation, and then under a concurrent schedule of food presentation and shock presentation. In one monkey, when shocks (12.6 ma) followed each response during the last minute of an 11-min cycle ending with a timeout period, responding was increased during the first 10 min and suppressed during the last minute of each cycle. When the shock schedule was eliminated, both the enhancement and suppression disappeared, and a steady rate of responding was maintained under the variable-interval schedule. When the food schedule was eliminated, the shock schedule maintained a characteristic fixed-interval pattern of responding during the first 10 min, but suppressed responding during the last minute of each cycle. The fixed-interval pattern of responding was maintained when the timeout period was eliminated and when only one shock could occur at the end of the cycle. In the second monkey, responding under the concurrent food and shock schedule was suppressed when responses produced shocks after 3-min. Under an 11-min cycle, responding continued to be maintained at increasing shock intensities. When the food schedule was eliminated, a fixed-interval pattern of responding was maintained under a 10-min schedule of shock presentation (12.6 ma). Whether response-produced electric shocks suppressed responding or maintained responding depended on the schedule of shock presentation.

Maintenance of responding under a fixed-interval schedule of electric shock-presentation.

Squirrel monkeys trained to respond under a schedule in which each response postponed the delivery of electric shock developed a steady rate of responding. When a schedule in which an electric shock was presented following the first response occurring after 10 minutes (10-minute fixed-interval schedule) was programed concurrently, there was little effect on the pattern of responding. When the shock-postponement schedule was eliminated, the fixed-interval schedule of shock-presentation maintained a pattern of positively accelerated responding that is characteristic of fixed-interval schedules of reinforcement.

SCHEDULES USING NOXIOUS STIMULI. L MULTIPLE FIXED‐RATIO AND FIXED‐INTERVAL TERMINATION OF SCHEDULE COMPLEXES1

The termination of a schedule complex, comprising a stimulus in the presence of which brief presentations of electric shocks are scheduled, is a reinforcer. Conditions were studied under which schedule-controlled patterns of responding characteristic of fixed-interval, fixed-ratio, and multiple fixed-interval fixed-ratio schedules can be maintained in the squirrel monkey by terminating a schedule complex. The schedule of shock presentation was a critical determinant of the patterns of responding, especially under fixed-interval schedules of termination. The rates and patterns of responding under various schedules of termination of schedule complexes were generally akin to those maintained under comparable schedules of food presentation. The findings suggest a general similarity in the dynamic aspects of performances under schedules of schedule-complex termination and comparable schedules of food presentation. The schedule of reinforcement is more important than the nature of the reinforcer in the control of behavior.