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PubMed1993

The role of nucleus accumbens dopamine in responding on a continuous reinforcement operant schedule: a neurochemical and behavioral study.

Two experiments were undertaken to investigate the role of nucleus accumbens dopamine (DA) in instrumental lever pressing on a continuous reinforcement (CRF) schedule. Rats trained to press a lever for food reinforcement on a CRF schedule, and food-deprived control rats, were implanted with dialysis probes in the nucleus accumbens. The day after implantation, rats were tested and dialysis samples were assayed for DA and the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC). Performance of the lever-pressing task resulted in significant increases in extracellular levels of DA and DOPAC relative to control rats. The increases in extracellular DA were significantly correlated (r = 0.92) with the number of lever press responses committed. In the second experiment, the neurotoxic agent 6-hydroxydopamine was infused directly into the nucleus accumbens to investigate the effects of DA depletion on lever-pressing performance. DA depletion had only a modest effect on the total number of lever presses, and there was a significant effect on total lever presses only on the first test day (third day postsurgery). Analyses also were performed on responding across the 45-min session by breaking down the session into three 15-min periods. There was a significant group x time interaction, with DA-depleted rats showing a significant reduction in the numbers of responses in the first 15-min period, but no significant effects over the second or third 15 min in the session. This initial slowing of response rate was present across all 5 test days. These results indicate that DA release and metabolism increases in rats performing on a CRF schedule, and that DA depletion produces a slowing of initial response rate.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2000

A within-subject comparison of three different schedules of reinforcement of drug abstinence using cigarette smoking as an exemplar.

In this experiment we compared three different schedules of reinforcement for promoting and sustaining short-term drug abstinence. For pragmatic reasons, cigarette smoking was studied as an exemplar of drug self-administration. The three schedules studied were a fixed magnitude of reinforcement for abstinence, a progressive increase in magnitude of reinforcement for abstinence with a reset contingency for drug use, and a progressive increase in magnitude of reinforcement for abstinence without a reset contingency. Eighteen cigarette smokers experienced the three schedules in a counterbalanced order. Each schedule was in effect for 5 consecutive days (M-F), during which time abstinence was reinforced according to the different schedules of reinforcement. The total amount of reinforcement (money) available was the same during each condition. The progressive magnitude with a reset schedule was more effective than the other two schedules in sustaining an initial period of abstinence. These results systematically replicate and extend those from prior studies demonstrating the efficacy of schedules incorporating a progressively increasing magnitude of reinforcement with a reset contingency for sustaining initial drug abstinence, and demonstrate the importance of the reset contingency to that effect.

Adult↗
PubMed2005

Effects of the competitive N-methyl-D-aspartate receptor antagonist, LY235959 [(-)-6-phosphonomethyl-deca-hydroisoquinoline-3-carboxylic acid], on responding for cocaine under both fixed and progressive ratio schedules of reinforcement.

It is difficult to determine the precise role of the N-methyl-D-aspartate (NMDA) receptor system in the reinforcing effects of cocaine since uncompetitive NMDA receptor antagonists alter cocaine self-administration in different ways, depending on the antagonist examined and the behavior being measured. To increase understanding of the role of the NMDA system in cocaine's reinforcing effects, this study measured the effects of the competitive NMDA receptor antagonist, LY235959 [(-)-6-phosphonomethyl-deca-hydroisoquinoline-3-carboxylic acid], in rats that self-administered cocaine under both fixed ratio (FR) 1 and progressive ratio (PR) schedules of reinforcement. Rats were trained to self-administer cocaine (0.33 mg/infusion) under an FR1 schedule of reinforcement. Thereafter, the effects of pretreatment with LY235959, or the uncompetitive antagonists dextromethorphan and dizocilpine, were examined. The number of infusions earned during the first 10 min of responding under the FR1 schedule was analyzed separately. When rats responded for 0.33 mg/infusion cocaine under an FR1 schedule of reinforcement, 3 mg/kg LY235959 decreased cocaine self-administration only during the first 10 min of the responding. This effect was dose and time dependent and blocked by the competitive NMDA receptor agonist, NMDA. LY235959 (3 mg/kg) decreased total responding for cocaine only when the self-administered dose of cocaine was small (0.02-0.04 mg/infusion) or when responding was reinforced under the PR schedule. In contrast, dizocilpine decreased responding under the FR1 schedule but increased responding under the PR schedule. These data suggest that LY235959 decreased the reinforcing effectiveness of cocaine, a finding reported with systemically administered NMDA receptor antagonists other than dizocilpine.

Animals↗
PubMed1971

Two-key concurrent paced variable-interval paced variable-interval schedules of reinforcement.

Nine pigeons were used in two experiments in which a response was reinforced if a variable-interval schedule had assigned a reinforcement and if the response terminated an interresponse time within a certain interval, or class, of interresponse times. One such class was scheduled on one key, and a second class was scheduled on a second key. The procedure was, therefore, a two-key concurrent paced variable-interval paced variable-interval schedule. In Exp. I, the lengths of the two reinforced interresponse times were varied. The relative frequency of responding on a key approximately equalled the relative reciprocal of the length of the interresponse time reinforced on that key. In Exp. II, the relative frequency and relative magnitude of reinforcement were varied. The relative frequency of responding on the key for which the shorter interresponse time was reinforced was a monotonically increasing, negatively accelerated function of the relative frequency of reinforcement on that key. The relative frequency of responding depended on the relative magnitude of reinforcement in approximately the same way as it depended on the relative frequency of reinforcement. The relative frequency of responding on the key for which the shorter interresponse time was reinforced depended on the lengths of the two reinforced interresponse times and on the relative frequency and relative magnitude of reinforcement in the same way as the relative frequency of the shorter interresponse time depended on these variables in previous one-key concurrent schedules of reinforcement for two interresponse times.

Journal Article↗
PubMed1992

Discriminative-stimulus control by morphine in the pigeon under a fixed-interval schedule of reinforcement.

The stimulus control by morphine under a fixed-interval (FI) 180-s schedule of reinforcement was examined in five pigeons trained to discriminate 5.0mg/kg of i.m. morphine from saline. After training, dose-response relationships were determined for morphine, d-amphetamine, pentobarbital, fentanyl, and MK-801. At low doses of morphine, responding of individual subjects was predominantly on the saline-appropriate key. At intermediate doses responding occurred on both keys throughout the interval. Following doses of 5.6mg/kg and higher, responding on both keys was observed in the early portions of the interval with responding shifting to the morphine-appropriate key as the interval progressed. Thus, a graded dose-effect curve for morphine was obtained under the FI schedule. The fentanyl dose-effect curve was similar to that obtained with morphine, but the other test drugs were not generalized. Five other pigeons were trained to discriminate 5.0mg/kg of morphine from saline under a fixed-ratio (FR) 100 schedule of reinforcement. During testing with morphine, responses were confined to the saline-appropriate key at 0.3 and 1.0mg/kg of morphine, but at higher doses responses were confined to the drug key. In contrast to the results obtained using the FI schedule, a quantal relationship for responding on the two keys was observed when a FR schedule was employed.

Journal Article↗
PubMed1966

Some effects on generalization gradients of tandem schedules.

The relationship between training conditions and stimulus generalization gradients was examined using tandem schedules of reinforcement. Schedules were selected so that frequency of reinforcement and rate of responding were varied somewhat independently of each other. A peak-shift in the generalization gradient was obtained when extinction had been associated with one of the stimuli. No comparable peak shift was obtained when there were equal response rates in the training stimuli even with dissimilar frequencies of reinforcement. The data imply that response rates at the end of training, rather than reinforcement frequency per se, determine the characteristics of the generalization gradient.

Animals↗
PubMed1978

Local response-rate constancy on concurrent variable-interval schedules of reinforcement.

Concurrent variable-interval schedules were arranged with a main key that alternated in color and schedule assignment, along with a changeover key on which a small fixed ratio was required to changeover. Acceptable matching was observed with pigeons in two replications, but there was a tendency toward overmatching. Local response rates were found to differ for unequal schedules of a concurrent pair: local response rate was greater for the variable-interval schedule with the smaller average interreinforcement interval, but qualifications based on an interresponse-time analysis were discussed. In a second experiment, two 3-minute variable-interval schedules were arranged concurrently, and the experimental variable was the changeover procedure: either a changeover delay was incurred by each changeover or a small fixed ratio on a changeover key was required to complete a changeover. Changeover delays of 2 and 5 seconds were compared with a fixed-ratio changeover of five responses. The response output on the main key (associated with the variable-interval schedules) was greater when a changeover delay was arranged than when a fixed ratio was required to changeover. A detailed analysis of stripchart records showed that a 2-second delay generated an increased response rate for 3 seconds after a changeover, while the fixed-ratio requirement generated an increased rate during the first second only, followed by a depressed response rate for 2 seconds.

Journal Article↗
PubMedDate not supplied

What is a "schedule of reinforcement"?

Several ambiguities in the present terminology of behavior theory obscure some important theoretical assumptions and experimental details in current research. Left unclarified, such ambiguities impede the accurate analysis of laboratory procedures, and prevent reliable communication among researchers. This paper focuses on the term "schedule of reinforcement". It points out that two distinguishable operational rules are implicated in the term: in the case where reinforcement is of the so-called response contingent type, the "schedule" is really a rule to identify the response to be reinforced; in the case of non-contingent reinforcement, the "schedule" is truly a rule for delivery of reinforcement. Other terminological ambiguities that are encountered in a discussion of this term include "reinforcement" and "intermittency." A resolution of these problems will necessarily involve the procedures of non-contingent reinforcement, and the parameter of reinforcement probability.

Conditioning, Classical↗
PubMed1970

Interresponse time duration in fixed-interval schedules of reinforcement: control by ordinal position and time since reinforcement.

The times between each of the first thirteen responses after reinforcement (the first twelve interresponse times) were determined for two pigeons whose pecking was reinforced on fixed-interval schedules of food reinforcement ranging from 0.5 min to 5 min. These interresponse times were classified with respect to their ordinal position in the sequence of responses and with respect to the time since the preceding reinforcement at which the initiating response occurred. The median interresponse time durations were essentially constant after the sixth response after reinforcement regardless of the time at which the interresponse time was initiated. The durations of the first few interresponse times after reinforcement decreased as the number of preceding responses increased and as the time since the preceding reinforcement increased.

Journal Article↗
PubMed1979

Dorsal bundle extinction effect: motivation or attention?

Male albino Wistar rats were injected bilaterally with 4 micrograms of 6-hydroxydopamine into the dorsal noradrenergic bundle to deplete forebrain noradrenaline to less than 5% of control values. Acquisition learning of a fixed interval schedule or a continuously reinforced schedule was not altered but resistance to extinction was seen after food reinforced training on either schedule but not after water reinforced training. A possible increase in food motivation was tested by the use of preloading with free food prior to a fixed interval session but both control and lesioned rats reacted similarly to this manipulation thus appearing to exclude an increase in food motivation. An attentional explanation is proposed and tested by the demonstration that resistance to extinction does not occur after a partially (variable ratio 4), as opposed to a continuously, reinforced schedule. Further evidence in favour of an attentional mechanism comes from the finding that on both a fixed interval and a continuously reinforced schedule the lesion has to be present during the acquisition phase to result in subsequent resistance to extinction. Intact animals trained on either schedule and subsequently subjected to the lesion failed to show an increased resistance to extinction.

Animals↗
PubMed1990

Performance of children under a multiple random-ratio random-interval schedule of reinforcement.

Three children, aged 1.5, 2.5, and 4.5 years, pressed telegraph keys under a two-component multiple random-ratio random-interval schedule of reinforcement. In the first condition, responses on the left key were reinforced under a random-interval schedule and responses on the right key were reinforced under a random-ratio schedule. In the second condition, the schedule components were reversed. In the third condition, the original arrangement was reinstated. For all subjects, rates of responding were higher in the random-ratio component despite higher rates of reinforcement in the random-interval component. The average interreinforcement interval of the random-interval component was increased in the fourth condition, resulting in more similar rates of reinforcement for both schedule components, and then returned to its original value in the fifth condition. In both conditions, all subjects continued to exhibit higher rates of responding in the ratio component than in the interval component. Although these observations are consistent with results from studies with pigeons, it is argued that the response-rate differences between the interval and ratio schedule components are sufficient to demonstrate schedule sensitivity.

Journal Article↗
PubMed1983

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.

Adolescent↗
PubMed2000

Heroin self-administration under a second-order schedule of reinforcement: acquisition and maintenance of heroin-seeking behaviour in rats.

RATIONALE: Second-order schedules of heroin self-administration provide a method of measuring heroin-seeking behaviour independently of the effects of the drug on motor behaviour and of investigating the role of heroin-associated stimuli in such heroin-seeking behaviour. OBJECTIVES: These experiments aimed to establish a second-order schedule of heroin self-administration in rats, similar to that already established in this laboratory for cocaine self-administration and to investigate the role of discrete heroin-associated stimuli in the maintenance of heroin-seeking behaviour under a second-order schedule of reinforcement. METHODS: Heroin i.v. self-administration (0.04 mg/infusion) was initially contingent upon a lever press, and each infusion was paired with presentation of a 20-s light-conditioned stimulus (CS). Following acquisition of heroin self-administration, the response requirement was progressively increased so that, ultimately, responding was maintained under a fixed interval (FI) 15 min [fixed ratio (FR)5:S] second-order schedule. The effects of varying the dose of heroin (0.01 mg and 0.08 mg/infusion) and pre-treatment with the mu-opiate receptor antagonist, naloxone, on responding under a FI15(FR5:S) schedule were investigated. In addition, the role of the heroin-associated CS on responding was assessed by measuring the effects of omitting the CS during heroin-seeking behaviour and during extinction of responding, as well as the effect of CS presentation on the reinstatement of heroin-seeking behaviour following extinction. RESULTS: A second-order schedule of heroin self-administration was established. There were no clear effects on heroin-seeking behaviour of increasing or decreasing the dose of heroin. Although no effect of naloxone pre-treatment was seen on heroin-seeking behaviour during the first, drug-free interval of responding, an extinction-like pattern of responding was seen in that interval during subsequent sessions. Omission of the light CS resulted in a reduction in levels of responding for i.v. heroin, indicating its role in maintaining heroin-seeking behaviour. However, under extinction conditions, response-contingent CS presentations did not affect the rate of extinction, nor did non-contingent presentations of the CS following extinction reinstate heroin-seeking behaviour. CONCLUSIONS: These experiments have established a method of measuring heroin-seeking behaviour in rats by adopting a second-order schedule of i.v. heroin self-administration. The results indicate a relatively weak impact of discrete, heroin-associated cues on heroin-seeking behaviour relative to cocaine-seeking behaviour studied under similar conditions.

Animals↗
PubMed1995

Effects of remoxipride, an atypical antipsychotic, on cocaine self-administration in the rat using fixed- and progressive-ratio schedules of reinforcement.

Remoxipride, a selective D2-dopamine receptor antagonist with preferential activity for mesolimbic-mediated behaviors, was assessed for its potential to block cocaine self-administration. The effects of remoxipride (RMX) were evaluated using fixed-ratio-1 (FR-1) and progressive-ratio (PR) schedules of reinforcement. On FR-1, RMX pretreatment increased the rate of cocaine injections, while on a PR, breaking points were reduced. Daily RMX treatment also resulted in breaking point reductions, but the decreases in cocaine's reinforcing potency did not result in extinction of cocaine intake and were not sustained upon cessation of RMX. Thus, RMX can reduce the rewarding effects of cocaine, and if safely tolerated over sustained periods of treatment it, or drugs with a similar pharmacological profile, could provide a therapeutic adjunct in the treatment of cocaine addiction.

Animals↗
PubMed1996

Effect of pimozide on self-stimulation threshold under a continuous and fixed-interval schedule of reinforcement.

Rats implanted with a monopolar electrode in the medial mesencephalon and trained to press a lever to self-administer trains of stimulating pulses were tested under a continuous (CRF) and a fixed interval (FI-1s) schedule of reinforcement before and after systemic pimozide injection (0.35 mg/kg). As previously shown, this dose of pimozide caused reductions in maximal response rates and in the rewarding effectiveness of the stimulation. The magnitude of the attenuation in rewarding effectiveness was significantly greater under CRF than under FI conditions, an effect that can be attributed to the decrease in the number of earned rewards concomitant to a decrease in response rates. The present results show that the tighter control over reward density provided by the use of a FI schedule of reinforcement reduces the probability of artifactually measuring increases in reward thresholds following treatments that suppress response rates.

Animals↗
PubMed1973

Synthetic variable-interval schedules of reinforcement.

Three pigeons pecked for food on a synthetic variable-interval schedule of reinforcement that had two independent parts: a variable-interval schedule that arranged a distribution of interreinforcement intervals, and a device that randomly assigned each reinforcement to one of 10 classes of interresponse times. The frequencies of reinforcement for the 10 classes of interresponse times were systematically varied, while the overall frequency of reinforcement was held within a comparatively narrow range. The 10 classes extended either from 0.1 to 0.6 sec in 0.05-sec intervals, or from 1.0 to 6.0 sec in 0.5-sec intervals. In the former case, some control by reinforcement was obtained, but it was weak and no simple relationships were discernible. In the latter case, the relative frequency of an interresponse time was a generally increasing function of its relative frequency of reinforcement, and two simple controlling relationships were found. First, the function relating interresponse times per opportunity to reinforcements per opportunity was, over a restricted range, approximately linear with a slope of unity. Second, when all 10 classes of interresponse times were reinforced equally often, the relative frequency of an interresponse time approximately equalled the relative reciprocal of its length.

Journal Article↗
PubMed1983

Action of antidepressants, stimulants and depressants in the transition from a fixed ratio to a fixed interval schedule of reinforcement.

1. The modifications of rat behaviour caused by imipramine, amitriptyline, doxepin, amphetamine, chlorpromazine, caffeine and diazepam were studied. 2. The schedule of reinforcement was changed from a fixed ratio to a fixed interval schedule. 3. All the studied drugs caused a depression of the rat behaviour but only tricyclic antidepressants and caffeine caused virtually no damage to the ability of the animal to adapt its behaviour to the new experimental situation.

Amitriptyline↗