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PubMed1999

Withdrawal following repeated exposure to d-amphetamine decreases responding for a sucrose solution as measured by a progressive ratio schedule of reinforcement.

Numerous studies have shown that withdrawal from sustained high doses of psychostimulant drugs such as cocaine or d-amphetamine produces depressive-like symptoms in both rats and humans. The majority of experiments with rodents have assessed the effects of amphetamine withdrawal on reinforcing electrical self-stimulation in different brain regions, but relatively few have examined effects on responding for natural reinforcers. In the present study, two groups of mildly food and water deprived male rats were trained to respond on a lever for a 4% sucrose solution under a progressive ratio schedule of reinforcement. One group was subsequently administered a 4-day regimen of injections of increasing doses of d-amphetamine based on a schedule shown previously to reduce self-stimulation behaviour. Break points were significantly reduced for up to 4 days after the termination of drug administration, suggesting a decreased motivation to obtain the natural reward. A further experiment demonstrated that the identical drug regimen produced no effect upon consumption of the 4% sucrose solution when it was freely available. These results demonstrate that the progressive ratio procedure may be a useful technique for evaluating changes in motivation for natural reinforcing stimuli following withdrawal from psychostimulant drugs.

Animals↗
PubMed2004

Nucleus accumbens neurons in the rat exhibit differential activity to conditioned reinforcers and primary reinforcers within a second-order schedule of saccharin reinforcement.

The nucleus accumbens has been associated with processing information related to primary reinforcement and reward. Most neurophysiological studies report that nucleus accumbens neurons are phasically excited in response to the onsets of salient events during the seeking of reinforcement and to the delivery of primary reinforcers. However, a minority of studies report inhibition during primary reinforcement. We recorded from 65 neurons in the nucleus accumbens whilst thirsty rats performed under a second-order schedule of saccharin reinforcement. This allowed us to analyse neural activity and behaviour during reinforcer-seeking in the presence of conditioned reinforcers (second-order stimuli, also called 'conditioned stimuli'), and during primary reinforcer consumption. Specifically, we sought to examine the valence of potential neural responses to primary reinforcement, to compare these responses to second-order stimulus-evoked responses, and to determine whether responses were differential to second-order stimuli presented at different time points within the schedule. Fifty out of 65 neurons we sampled responded to the second-order stimulus and/or consumption of the primary reinforcer. Most neurons in our sample exhibited excitation following the second-order stimulus and inhibition to the primary reinforcer, a pattern also present over the average response of the neural population. However, there was no systematic variation in neural responses evoked by second-order stimuli presented at different temporal proximities to primary reinforcement. Our results provide evidence that partially overlapping mechanisms within the nucleus accumbens differentially process conditioned reinforcers and primary reinforcers.

Action Potentials↗
PubMed1991

Neurochemical changes correlated with behavior maintained under fixed-interval and fixed-ratio schedules of reinforcement.

Key pecking of 4 pigeons was maintained under a multiple 3-min fixed-interval, 30-response fixed-ratio schedule of food presentation. Only one schedule was in effect during an experimental session, and each was correlated with a different keylight stimulus and location (left vs. right). The different schedule components alternated across days or weeks. Cerebrospinal fluid was collected from chronically implanted intracerebroventricular cannulae following sessions with the different schedules, as well as following sessions in which reinforcement was withheld (extinction), when response-independent food was delivered, and when the experimental chamber was dark and there were no scheduled events. Metabolites of the neurotransmitters serotonin, norepinephrine, and dopamine were assayed in cerebrospinal fluid using high-performance liquid chromatography with electrochemical detection. Compared to the fixed-ratio condition, responding maintained under the fixed-interval schedule resulted in consistently higher levels of the serotonin metabolite 5-hydroxyindoleacetic acid and of the dopamine metabolite homovanillic acid in all pigeons. Levels of 3-methoxy-4-hydroxyphenylethylene glycol, a metabolite of norepinephrine, and dihydroxyphenylacetic acid, another dopamine metabolite, were also higher in 3 of the 4 pigeons following exposure to the fixed-interval schedules when compared to levels of these metabolites after exposure to the fixed-ratio schedule. Extinction of fixed-ratio responding resulted in large increases in 5-hydroxyindoleacetic acid compared to levels of this metabolite under the fixed-ratio schedule, whereas this serotonin metabolite decreased during extinction of responding under the fixed-interval schedule. Control procedures suggested that the neurochemical changes were not related to the rate of responding but were a function of the specific experimental conditions. Distinctive neurochemical changes that accompany schedule-controlled responding show the sensitivity of the neurochemical environment to behavioral contingencies and demonstrate further the profound impact that such contingencies have on biobehavioral processes.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1965

BRAIN STIMULATION AS A REINFORCER: INTERMITTENT SCHEDULES.

Rats with chronically implanted, bipolar electrodes in the septal and medial forebrain bundle areas, in addition to the region of the mammillary bodies of the posterior hypothalamus, were trained to press a permanently mounted lever in order to produce a second, retractable lever. Rewarding brain stimulation was programmed on the retractable lever; following completion of the programmed number of CRF response-stimulations, that lever was retracted from the box. Responding on the permanent lever could reintroduce the retractable lever. Fixed interval, fixed ratio, DRL, and variable interval schedules were programmed on the permanent lever in the range of schedule parameters often used with conventional reinforcers. Typical effects are described, and it is concluded that there are no striking differences between brain-stimulation reinforcement and the conventional reinforcers.

Brain↗
PubMed1970

Preference for fixed-interval schedules of reinforcement.

Pigeons were trained on a two-link concurrent chain schedule in which responding on either of two keys in the initial link occasionally produced a terminal link, signaled by a change in the color of that key and a darkening of the other. Further responding on the lighted key was reinforced with food according to a fixed-interval schedule. For one of the keys, this fixed interval was always 20 sec, while for the other it was held at values of 5, 14, 30, or 60 sec for several weeks. In the initial link, all pigeons responded relatively more often on the key with the shorter fixed interval than was predicted by the matching hypothesis. Responding in the initial link showed a large negative recency effect: pigeons responded less frequently on the key that provided their last reinforcement than predicted from the overall response rates.

Journal Article↗
PubMed2001

The long-term effect of high- and low-rate responding histories on fixed-interval responding in rats.

Tell rats were given extended lever-press training on a fixed-interval (FI) 30-s food reinforcement schedule from the outset or following exposure to one or two previous reinforcement schedules. For 4 rats the previots schedule was either fixed-ratio 20, which generated high response rates, or differential-reinforcement-of-low-rate 20 s, which produced low response rates. For 4 additional rats the extended training on FI 30 s was preceded by experience with two schedules: fixed-ratio 20 followed by differential-reinforcement-of-low-rate 20 s; or the same two schedules in the reverse order. Fixed-interval response rates were initially affected by the immediately preceding schedule, but after 80 to 100 sessions, all traces of prior schedule history had disappeared. The results also showed no long-term effect of schedule history on the interfood-interval patterns of responding on the FI 30-s schedule. These results support one of the most central tenets of the experimental analysis of behavior: control by the immediate consequences of behavior.

Animals↗
PubMed2000

Preference for unreliable reinforcement in children with mental retardation: the role of conditioned reinforcement.

We examined the effects of conditioned reinforcement on children's choice between reliable (100%) and unreliable (50%) reinforcement under various stimulus conditions in a concurrent-chains procedure. The study was conducted across three experiments. Experiments 1 and 2 were conducted under conditions similar to basic laboratory work and consisted of participants selecting from one of two black boxes (placed on a table) that were correlated with different reinforcement schedules. In Experiment 3, we assessed a participant's preference for unreliable reinforcement during conditions in which the target responses were aggression and mands. Results of the three experiments showed that the participants preferred unreliable reinforcement under certain conditions. Findings are discussed regarding the role of specific stimuli (i.e., items correlated with a reinforcement schedule, adult reactions) as conditioned reinforcers and how they may influence children's preference for a response (e.g., aggression, self-injury) that produces reinforcement on a leaner schedule than a socially desirable response (e.g., mands).

Aggression↗
PubMed1993

Performances on ratio and interval schedules of reinforcement: Data and theory.

TWO DIFFERENCES BETWEEN RATIO AND INTERVAL PERFORMANCE ARE WELL KNOWN: (a) Higher rates occur on ratio schedules, and (b) ratio schedules are unable to maintain responding at low rates of reinforcement (ratio "strain"). A third phenomenon, a downturn in response rate at the highest rates of reinforcement, is well documented for ratio schedules and is predicted for interval schedules. Pigeons were exposed to multiple variable-ratio variable-interval schedules in which the intervals generated in the variable-ratio component were programmed in the variable-interval component, thereby "yoking" or approximately matching reinforcement in the two components. The full range of ratio performances was studied, from strained to continuous reinforcement. In addition to the expected phenomena, a new phenomenon was observed: an upturn in variable-interval response rate in the midrange of rates of reinforcement that brought response rates on the two schedules to equality before the downturn at the highest rates of reinforcement. When the average response rate was corrected by eliminating pausing after reinforcement, the downturn in response rate vanished, leaving a strictly monotonic performance curve. This apparent functional independence of the postreinforcement pause and the qualitative shift in response implied by the upturn in variable-interval response rate suggest that theoretical accounts will require thinking of behavior as partitioned among at least three categories, and probably four: postreinforcement activity, other unprogrammed activity, ratio-typical operant behavior, and interval-typical operant behavior.

Journal Article↗
PubMed1980

Persistence: the role of partial reinforcement in psychotherapy.

Persistence, which refers to the ability of a learned behavior to survive protracted nonreinforcement (extinction), has been an overlooked dimension of clinical intervention. While persistence of newly acquired coping behavior is desired (and possibly assumed) by all psychotherapeutic procedures, few treatment programs possess features that operate to sustain responding in the face of a nonsupportive, nonreinforcing environment. The present article presents a treatment strategy designed to foster persistence based on the laboratory findings that partial reinforcement schedules produce greater resistance to extinction than continuous reinforcement schedules--a phenomenon referred to as the partial reinforcement extinction effect. The two major theories of persistence (Amsel's general theory of persistence and Capaldi's sequential theory) are discussed, and the basic principles of these models are extended to a number of therapeutic modalities including depression therapies, systemic desensitization, assertiveness training, and aversion therapy. In addition, procedural considerations including generalized and discriminated persistence are discussed.

Adaptation, Psychological↗
PubMed1977

Effects of schedules of reinforcement on brain catecholamine metabolism in the rat.

Rats were trained on a fixed ratio 5 (FR 5) for 0.01 ml water reinforcer, a fixed ratio 20 (FR' 20) for 0.01 ml water reinforcer, a fixed ratio 20 (FR 20) for 0.04 ml water reinforcer, a variable time 15 sec (VT 15 sec) for 0.01 ml water reinforcer, a variable time 30 sec (VT 30 sec) for 0.01 ml water, variable time 60 sec (VT 60 sec) for 0.01 ml water, or a variable time 60 sec (VT 60 sec) for 0.10 ml water. In all these schedules, the rate of NE metabolism varied with the number of water presentations but not with the number of responses or the volume of water. The rate of metabolism of DA was increased over control values in rats on the VT schedules but no significant differences could be found in DA metabolism among the rats performing on the various VT schedules or receiving various volumes.

Animals↗
PubMed2000

Intravenous self-administration of methamphetamine-heroin (speedball) combinations under a progressive-ratio schedule of reinforcement in rats.

The i.v. self-administration by rats of a polydrug combination of methamphetamine and heroin was explored. The rewarding efficacy of a range of methamphetamine doses (0.0625-2.0 mg/kg/injection) alone or in combination with heroin (12.5 microg/kg/injection) was compared using a progressive-ratio (PR) schedule of reinforcement. Breaking points (BP) for one group of rats were determined at each dose of methamphetamine-alone and for another group at each of the same methamphetamine doses plus the heroin dose. The methamphetamine-heroin combination was associated with higher BPs than methamphetamine alone at all doses of methamphetamine. These data demonstrate that methamphetamine-heroin combinations (speedballs) produce a greater rewarding effect than the identical doses of methamphetamine alone and suggest that enhanced reward may underlie the popularity of speedball abuse.

Animals↗
PubMed1978

d-amphetamine and fixed-interval performance: effects of operant history.

Sixteen rats were initially exposed for 50 sessions to either a fixed-ratio 40 or an interresponse-time-greater-than-11-second food reinforcement schedule, then shifted to a fixed-interval 15-second food reinforcement schedule. Animals with fixed-ratio 40 histories lever pressed at much higher rates under the fixed-interval schedule than did animals with inter-response-time-greater-than-11-second histories. This difference persisted across 93 sessions of fixed-interval exposure. The effects of d=amphetamine were assessed after 15 and 59 sessions of fixed-interval exposure. On both occasions, the low-rate responding of animals with interresponse-time-greater-than-11-second histories was typically increased by all doses of the drug, while the high-rate responding of animals with fixed-ratio 40 histories was typically decreased by all doses of the drug. These results suggest that control response rate under the fixed-interval schedule, which may be affected by a history of responding under another schedule, is the primary determinant of the relative effects of d-amphetamine.

Animals↗
PubMed1963

PREDICTION OF DISCRIMINATION FROM GENERALIZATION AFTER VARIATIONS IN SCHEDULE OF REINFORCEMENT.

The relationship between generalization and discrimination is explored in the present study by utilizing the results of systematic changes in the generalization gradient to predict changes in discrimination behavior. In the first of two experiments, differing groups of pigeons were trained to respond to a wavelength of 550 mmicro under conditions of varying schedules of reinforcement. Generalization gradients were then obtained and the ratios of the responses to selected discriminative stimuli calculated. These were used to predict discrimination behavior in a second experiment using the same stimuli. Both the number of trials to a discrimination criterion and the ratio of response indicate the plausibilty of an inverse hypothesis, and the applicability of the generalization model to related behavior such as discrimination.

Animals↗
PubMed1980

Contingency and stimulus change in chained schedules of reinforcement.

Higher rates of pecking were maintained by pigeons in the middle component of three-component chained fixed-interval schedules than in that component of corresponding multiple schedules (two extinction components followed by a fixed-interval component). This rate difference did not occur in equivalent tandem and mixed schedules, in which a single stimulus was correlated with the three components. The higher rates in components of chained schedules demonstrate a reinforcing effect of the stimulus correlated with the next component; the acquired functions of this stimulus make the vocabulary of conditioned reinforcement appropriate. Problems in defining conditioned reinforcement arise not from difficulties in demonstrating reinforcing effects but from disagreements about which experimental operations allow such reinforcing effects to be called conditioned.

Journal Article↗
PubMed1974

Absence of shock-elicited aggression in pigeons.

Two pigeons that attacked a taxidermically prepared target pigeon during a schedule of positive reinforcement for key pecking, and two that did not, were shocked through implanted electrodes in the presence of the target. Shock intensities of 2 and 4 mA, durations of 0.1 and 1.3 sec, and frequencies of 2, 6, 20, and 35 per minute were delivered across 16 sessions with 180 shocks per session. No pigeon attacked the target; one pecked the shockplug on its back. The two pigeons that had not attacked during the positive reinforcement schedules were conditioned to peck the target for food reinforcement before another 16 sessions of shock. No attack was observed in these shock sessions. During subsequent positive reinforcement of key pecking, the target was attacked by the two pigeons that had originally attacked and by one that had not. Absence of shock-elicited attack in these pigeons may be related to the parameters of the experiment or may be yet another instance of the absence of shock-elicited attack in the class Aves. At least under the present conditions, it was not possible to predict the level of attack during electric shock from the level of attack during schedules of positive reinforcement for key pecking.

Aggression↗
PubMed1994

Butorphanol increases food-reinforced operant responding in satiated rats.

In the present series of studies we examined the effect of butorphanol tartrate on food-reinforced operant responding in satiated rats. In the first experiment, 8.0 mg/kg butorphanol was administered subcutaneously, once per day for 4 days, to satiated rats responding under an fixed ratio 10 (FR 10) reinforcement schedule. In the second experiment, butorphanol (0, 0.3, 1.0, 3.0, 10.0 mg/kg) was administered to satiated rats responding under an FR 80 (first pellet) FR 3 (subsequent pellets) reinforcement schedule for 4 consecutive days. Repeated butorphanol administration increased total amount of food consumed over sessions in both experiments. Under the FR 80 schedule component, butorphanol initially increased latency to acquire the first pellet, an effect attenuated by repeated administration. Whereas vehicle administration was associated with consumption of relatively large quantities of food within the first 10 min of receiving the first pellet, butorphanol was associated with continued feeding as the session progressed. These data suggest that butorphanol-induced food intake is associated with maintenance rather than initiation of feeding.

Animals↗
PubMed1978

The effect of foreperiod duration on reaction time and its relation to interval schedules of reinforcement.

Two groups of pigeons were exposed to a simple reaction-time procedure in which mean foreperiod duration was 5, 10, or 20 seconds. For one group, the foreperiods had an arithmetic, or rectangular, distribution; for the second group, they had a constant-probability, or Bernoulli, distribution. Under both distributions, mean response latency was an increasing, negatively accelerated function of mean foreperiod duration. On a given trial, response latency was a function of its associated foreperiod duration: latency was a decreasing function of foreperiod duration in the arithmetic distribution, and an increasing function of foreperiod duration in the constant-probability distribution. Examination of the distribution of latencies revealed a harmonic structure reminiscent of distributions of interresponse times under variable-interval schedules of reinforcement. Taken together, the results confirm and extend previous findings with human subjects, and also suggest numerous similarities to behavior maintained by variable-interval schedules.

Journal Article↗