Operant Schedule Research Articles

Operant-Pavlovian interactions: The effect of the number of stimuli with free-food depends on the operant baseline

Four groups of three pigeons were trained to respond under operant schedules which varied with respect to response rate requirements and reinforcement frequency. The number of short duration stimuli preceding free food was manipulated in different experimental conditions. Operant behavior was maintained on one key, while stimuli were presented on another key. Stimulus key response rates, latencies to the first response on the stimulus key and the percentage of stimuli responded to did not vary as a function of the number of stimuli presented, but were dependent upon the reinforcement frequency of the operant baseline.

Discriminative control of hyperdipsic drinking in the baboon

A baboon subject was surgically prepared with an arterial catheter and subsequently trained to elevate diastolic blood pressure with an operant schedule of food procurement and shock avoidance with associated discriminative stimuli. Blood pressure elevations developed in accordance with the requirements of the conditioning procedure. In addition, large-scale increases in water intake occurred on days when the conditioning sessions were in effect. Both blood pressure and water intake elevations were maintained when the conditioning procedure was changed to eliminate food reinforcement. Electrical monitoring of water spout contacts revealed that drinking occurred exclusively during response-produced S Ds associated with food delivery, and did not occur either during response-produced S Ds associated with electric shock, or during intertrial intervals. Because acute elevations in blood pressure preceded licking bouts, the drinking was not producing the pressor episodes. Overall, the data illustrate that drinking can occur in a systematic manner under the control of exteroceptive discriminative stimuli during non-skeletal response contingencies.

A correction to Hull’s law on delay of reinforcement and its extension to fixed-interval operant schedules

Hull’s law on delay of reinforcement was corrected for internal consistency by testing the law against the data from which it was derived. Using these same data, the law was extended to be a function of trials. The resulting equation was extended further by mathematically transforming the latency of responding into the rate of responding, and equating the delay of reinforcement with the fixed interval of an operant schedule. The prediction of the transformed equation was that the logarithm of the rate of responding of an organism is a linear function of the logarithm of the number of trials or reinforcements, with the slope of this linear function being dependent upon the numerical value of the fixed interval.

Demonstration of basic concurrent-schedules effects with dogs: Choice between different amounts of food

Two experiments studied the ways dogs perform on concurrent operant schedules when choosing between different amounts of food. Experiment 1 allowed six dogs to choose between obtaining different amounts of food available for responding on two levers. Across phases of the experiment, the food amounts were available in four different weight-to-weight ratios, 1:1, 2:1, 3:1, and 4:1. The operant schedule was concurrent VI 60 sec VI 60 sec. The results showed that the dogs “undermatch” when the ratio of their responses on the two levers is plotted against the ratios of the amounts of food they produced by responding on those levers. When the response ratios were recomputed to include only those lever-presses that occurred outside the change-over delay (C.O.D.) period, the severity of undermatching was reduced, and the data averaged across all six dogs showed a matching function. Experiment 2 studied the effect of varying the duration of the C.O.D. when the dogs chose between food-amounts in a 3:1 weight-to-weight ratio. The number of times the dogs alternated between responding on the two levers per session was inversely related to the duration of the C.O.D., but the approximation to matching seems little affected.

The effects of lesions of the habenula nucleus on lever press behaviour during a tandem operant schedule with contrasting response requirements

The effect of bilateral lesions of the habenula nuclei in male Lister hooded rats was assessed in performance of a well learned complex tandem operant reinforcement schedule. The schedule requirement involved two successive and contrasting components in which 15 operant lever press responses followed by inhibition of the same response for a period of 15 s provided liquid-food reinforcement. Initially little disruption of performance was seen when each component of the schedule was differentially signalled with an external cue. However, relative to controls, lesioned animals showed an increasing disruption of performance when such cues were omitted. The deficit in performance of lesioned animals was not a simple failure to inhibit responding that could be predicted from an altered input from septal areas. It is suggested that these behavioural data are consistent with the anatomical evidence for the habenula as a functional relay for the integration of information from limbic structures and the striatum and that lesions of the habenula affect the ability of animals to maintain effective response strategies, particularly when these are under intrinsic control.

Hedonic scaling of sugars using concurrent operant schedules with dogs

An experiment is reported with 5 beagles in which the concurrent operants procedure was used to scale glucose and fructose against a “standard” sugar, sucrose. The sugars were in solution and the dogs were required to lever-press to obtain access to the solutions. In the first part of the experiment, the dogs chose between fructose and sucrose, and between glucose and sucrose, in a series of tests where different volumes of the two sugars were available for pressing the two levers. This arrangement made it possible to construct an empirical function for each pair of sugars showing the relation between relative strength of responding on the levers and the relative volumes of fluids obtained. From these functions it was possible to predict the ratio of fluid-volumes that would render hedonic equivalence. The data supported the prediction, indicating the ability of the concurrent schedules procedure to scale qualitatively different food-items in dogs.

Postsynaptic serotonergic blockade following chronic antidepressive treatment with trazodone in an animal model of depression

Acute pretreatment with clinically equivalent doses of antidepressive drugs has been observed to block D,L-5-hydroxytryptophan (5-HTP) induced behavioral depression in rats working on a food-reinforced operant schedule. Data from studies designed to distinguish presynaptic from postsynaptic events, indicated that the antidepressants were acting in part as blockers of postsynaptic serotonergic receptors. Using the same 5-HTP model of depression, we studied both the chronic and acute effects of a recently introduced antidepressant, trazodone, a triazolopyridine compound. Rats working for milk reinforcement and exhibiting behavioral depression following administration of 50 mg/kg 5-HTP were pretreated (one hr before 5-HTP) with 1, 2, or 4 mg/kg trazodone with resulting blockade of 5-HTP induced depression of 35, 62 and 70% respectively. Chronic administration of trazodone (2 mg/kg trazodone/day) also resulted in a significant blockade of the 5-HTP effect (75%). Neither 2 mg/kg or 4 mg/kg trazodone was found to potentiate the shorter period of depression following 25 mg/kg 5-HTP. Chronic treatment with the antidepressant drugs, amitriptyline or mianserin also blocked 5-HTP depression. Thus, as in our earlier studies, these data suggest an important postsynaptic mechanism associated with chronic administration of trazodone, amitriptyline and mianserin which could be implicated in the therapeutic effectiveness of these drugs. The potency of trazodone in relation to other antidepressant drugs in our behavioral model of depression paralleled their potency in displacing radioligand binding to 5-HT receptors, and gives additional support for the new hypersensitive postsynaptic serotonin receptor theory of depression.

Age-related preferences for paced and unpaced tasks in chained schedules of reinforcement.

Younger and older men were studied on chained operant schedules. A response in the initial link produced a terminal link where a sequence of 10 key presses was reinforced with money. In different conditions, the time available for each key press was varied from .5 sec to an unlimited amount, and the speed with which the men produced the terminal links containing the paced and unpaced sequences was taken as an index of preference for the terminal link conditions. When the men had difficulty adjusting to pacing, initial link speed was directly related to reinforcement rate in the terminal link: the greater the reinforcement, the faster the speed. This effect was stronger among the older men, who had more difficulty adjusting to pacing. With continued exposure to pacing, however, men of both ages adjusted more readily and the speed-reinforcement relationship decreased. These results suggest that the role of monetary reinforcement in determining task preferences is moderated by other factors such as task difficulty.

Attenuation of baroreflexes during operant cardiac conditioning.

ABSTRACTThree monkeys were trained to slow and to speed heart rate on an operant schedule. After the animals were performing highly reliably they received injections of nitroglycerin or phenylephrine to elicit baroreflexes during control periods and during slowing or speeding sessions. The findings were that each animal reliably attenuated its baroreflex sensitivity and thereby avoided shock. Thus, the data showed that under appropriate behavioral conditions homeostatic adjustments of the cardiovascular system are reduced.

Neurotoxic lesions of ventrolateral but not anteromedial neostriatum in rats impair differential reinforcement of low rates (DRL) performance

In two separate experiments, rats received either kainic acid (KA), 6-hydroxydopamine (6-OHDA) or control lesions bilaterally into either the anteromedial or ventrolateral neostriatum. Both ventrolateral neurotoxic lesions disrupted post-operative body weight regulation and the acquisition of a DRL-20 sec operant schedule of reinforcement. The pattern of operant responding suggested that these animals had an impairment in response sequencing or switching. Rats with anteromedial lesions manifested neither body-weight nor DRL impairments.

CONDITIONAL ACCELERATION AND EXTERNAL DISINHIBITION OF OPERANT LEVER PRESSING BY PREREWARD, NEUTRAL, AND REINFORCING STIMULI

Rats responding under a differential-reinforcement-of-low-rate schedule increased their rates of lever pressing during a 20-second click/flash stimulus that preceded the delivery of a response-independent food pellet. The increase could not be attributed to suppression of collateral behavior that has been said to mediate temporally-spaced responding. We propose that the prereward stimulus functioned as an external disinhibitor of lever pressing that had been inhibited by the constraints of the operant schedule. Support is derived from the observed disinhibitory effects of a 10-second unpaired click/flash stimulus and of unsignaled, response-independent pellets that were presented while the animals were responding under the same schedule.

Telephone operator scheduling with a fixed number of operators

A solution approach is presented for the following telephone operator scheduling problem: “Given a demand pattern for operators over a 24 hour period and the total number of available operators, determine the assignment of the available operators to work periods in order to provide an optimal service to customers”, An integer linear programming formulation is proposed to solve this problem. Using a general integer linear programming algorithm, computational results indicate that realistic sized scheduling problems can then be solved within a very low computation time. The solution generated by the optimization model can be further improved by manipulating the demand profile of the problem. Necessary information for this manipulation is obtained by solving the integer optimization problem without the integer restrictions.

Effects of chlorpromazine on continuous avoidance behavior in mice

Previous reports have indicated that self-trained appetitive operant schedules of reinforcement can be acquired readily by mice using an apparatus which detects head movement responses. Using a similar apparatus, suitably modified, the utility of this methodology has been extended to an operant schedule of reinforcement in which behavior is maintained by an aversive shock stimulus. As previously demonsrated with various other CNS active drugs in the appetitive mouse procedures, the effects of chlorpromazine in the mouse continuous avoidance procedure described here were similar to those obtained in analogous standard rat procedures. These results increase the opportunities for experimenters to avail themselves of the advantages offered by the use of mice, rather than rats, in operant behavioral pharmacology.

Xanthines alter behavior maintained by intracranial electrical stimulation and an operant schedule.

Caffeine and related alkylxanthines are widely used for recreation and therapeutic effects. In behavioral studies, both response rate-enhancing and attenuating effects have been described, depending upon the dose and behavioral measure used. Intracranial self-stimulation (ICSS) and differential reinforcement of low rates of responding (DRL) were assessed after rats were administered one of a range of doses of caffeine or aminophylline. These measures were chosen because of their demonstrated sensitivity to psychotropic drugs and the potential for comparing the alkylxanthine data to the extensive literature of amphetamine effects on ICSS and DRL behavior. Caffeine and aminophylline elicited dose- and drug-dependent changes in ICSS responding, and increased response rates and decreased reinforcements on the DRL schedule. These behavioral results are discussed with reference to alkylxanthine interactions with adenosine receptors.

Behavioral correlates of focal hippocampal x-irradiation in rats II. Behavior related to adaptive function in a natural setting.

Prior investigations have shown the effects of hippocampal degranulation on behaviors such as two-way avoidance, open-field behavior, and operant schedules of reinforcement. Little, however, has been done with behaviors related to adaptive function in a natural setting; the present study has addressed this issue. Long-Evans hooded rats, subjected to focal neonatal X-irradiation of the hippocampus, were tested in passive avoidance and four dominance situations. The experimental animals, which had approximately a 70% reduction in the granule cells of the hippocampal dentate gyrus, showed response perseveration in the passive avoidance task and were generally non-competitive in the dominance situations when compared to non-irradiated control animals. The single exception to this was noted in the test where an experimental rat and control animal were competing for a receptive female rat. Here the degranulated animals were strikingly superior to the control subjects with many more successful mounts. Some support for the response suppression model of hippocampal functioning was noted.

Concurrent Classical Conditioning

Concurrent classical conditioning, anticipated in the early writings of Pavlov, involves the simultaneous presentation of two previously established classical conditioning schedules. Pitting one set of delay conditioned responses against another results in a reciprocal or complementary inhibition between the stimulus orienting and consummatory responses separately elicited by each component. Concurrent classical conditioning also elicits complex response sequences which are qualitatively and quantitatively different from the unconditioned responses elicited by the appetitive reinforcers. The complementary inhibition and sequentially dependent elicitation of conditioned responses are similar to the response interdependencies obtained in concurrent operant schedules and concurrent classical-operant conditioning.

Central 5-hydroxytryptamine and the effects of hallucinogens and phenobarbital on operant responding in rats

The present study was designed to examine the role of 5-hydroxytryptamine (5-HT) neurons in the behavioral effects of d-lysergic acid diethylamide (LSD), an indolealkylamine hallucinogen, 2,5-dimethoxy-4-methylamphetamine (DOM) and mescaline, phenethylamine hallucinogens, and phenobarbital, a non-hallucinogen. Male rats, maintained at 70–80% of their free-feeding weights, were trained to press a lever for food pellet reinforcement on a fixed ratio-40 operant schedule. When trained, these rats responded at a constant, rapid rate (approximately 100 responses/min) during daily 40 min test sessions. Administrations of hallucinogens caused an abrupt cessation of responding (a “pause”), for some portion of the session. The duration of this pause was dose-dependent for LSD (12.5–100 μg/kg), DOM (0.125–1.0 mg/kg) and mescaline (7.1–14.2 mg/kg). On the other hand, phenobarbital (12.5–50 mg/kg) did not cause pausing, but resulted in slowed, erratic intrasession response rates. When the same tests were repeated in rats that had previously received an intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT) the dose-response curves for the pausing induced by all three hallucinogens were shifted to the left, while the behavioral disruption produced by phenobarbital was unaltered. In these animals the 5-HT but not the norepinephrine concentrations were markedly reduced in all brain regions examined. These results suggest that 5-HT neurons are involved with the behavioral effects of hallucinogens but not of phenobarbital.

Another psychophysical procedure: Within-trial stimulus thresholds

Discrete trial psychophysical procedures may be combined with tracking techniques and response pattern analysis to yield stimulus thresholds within each trial. In the present study, five pigeons were trained on a concurrent signalled reinforcement procedure, but with a variable rather than fixed intensity monochromatic blue light (470 nm) within each trial. Threshold was defined as stimulus intensity at the time of a response on the signal key. Trials with known response sequences of center key—signal key responses yielded more consistent thresholds relative to trials with unknown response sequences, with typical interquartile ranges of approximately 0.1–0.2 vs 0.3–0.4 log units, respectively. The threshold distribution was shifted as a direct function of prior exposure to blue-black fluorescent illumination of 15, 60, or 240 min, with the time to recover baseline thresholds a direct function of exposure duration. Discriminative stimuli in basic operant schedules might then be modified to yield stimulus-controlled response sequences which define within-trial thresholds amenable to psychophysical manipulation.

Naloxone potentiates the disruptive effects of mescaline on operant responding in the rat

Food-deprived male rats were trained to press a lever on a fixed ratio-40 (FR-40) operant schedule for food reinforcement. Administration of mescaline (4.0–10.0 mg/kg) immediately before the start of the operant session resulted in a cessation of responding for some portion of the 40-min period (“hallucinatory pause”). The duration of this pause was found to be dose-dependent. Although administration of naloxone alone (1.0–8.0 mg/kg, five minutes prior to start of the session) had no effect on FR-40 responding per se, pretreatment with this agent significantly potentiated the disruptive effects of mescaline. This potentiation by naloxone was further shown to be dose-dependent. These data suggest that the effects of the phenethylamine hallucinogen mescaline are potentiated by pretreatment with the narcotic antagonist naloxone.

Pre- and postsynaptic serotonergic manipulations in an animal model of depression

Rats working on a food-reinforced operant schedule and exhibiting behavioral depression following administration of D,L-5-hydroxytryptophan (5-HTP) were pretreated with one of three drugs: methysergide, fluoxetine, or amitriptyline. The former two drugs were used to establish a basis for distinguishing between pre- and postsynaptic events. We found that methysergide, a known postsynaptic blocker of serotonin, almost completely abolished the depressive effect of 5-HTP, whereas fluoxetine, a known specific uptake blocker of serotonin, potentiated the depressive effect of the 5-hydroxytryptamine (5-HT) precursor. Amitriptyline, one of the commonly prescribed antidepressive drugs, reduced the behavioral depression following 5-HTP by approximately 50%. These data indicate that amitriptyline can act as an antagonist of 5-HT at the postsynaptic receptor. The results of this study, as well as those recently reported from CNS membrane binding studies, suggest that the therapeutic effects of some antidepressive drugs may be explained by their postsynaptic rather than presynaptic properties at central serotonergic receptors. Thus, these studies support the hypothesis that some types of human depression may be primarily due to an excess of free 5-HT acting at postsynaptic receptors.