Fixed-interval Component Research Articles

Behavioral effects of cocaine alone and in combination with selective dopamine antagonists in the squirrel monkey

Effects of cocaine, alone and in combination with the dopaminergic antagonists, SCH 23390 and haloperidol were studied in squirrel monkeys trained to respond under fixed-interval schedules of electric-shock presentation. Cocaine at intermediate doses (0.1 and 0.3 mg/kg) increased rates of responding under the fixed-interval schedule and during 1-min timeout periods that separated each fixed-interval component. Higher doses (1.0 - 3.0 mg/kg) decreased response rates. Cocaine also dose-dependently altered the temporal pattern of responding characteristic of behavior under fixed-interval schedules. Haloperidol (0.003-0.1 mg/kg) and SCH 23390 (0.001-0.03 mg/kg) dose-dependently decreased rates of responding. A low dose (0.001 mg/kg) of the selective D1 antagonist, SCH 23390, did not appreciably alter the effects of cocaine. Higher doses (0.003-0.01 mg/kg), which when given alone decreased rates of responding, attenuated the increases in response rates produced by cocaine. In addition, the decreases in response rates produced by the higher dose of cocaine were attenuated by 0.01 mg/kg SCH 23390. The alterations in temporal patterning of responding under the fixed-interval schedule were not antagonized by any dose of SCH 23390. Haloperidol (0.003 mg/kg) did not appreciably alter the effects of cocaine; higher doses (0.01-0.03 mg/kg), which when given alone decreased rates of responding, attenuated the increases in response rates produced by 0.1 mg/kg cocaine. The decreases in response rates under the fixed-interval schedule that were produced by higher doses, or the changes in temporal patterning of responding at any dose of cocaine, were not antagonized by any dose of haloperidol that was studied.(ABSTRACT TRUNCATED AT 250 WORDS)

CONDITIONED REINFORCEMENT VERSUS TIME TO REINFORCEMENT IN CHAIN SCHEDULES

Pigeons were trained on three-component chain schedules in which the initial component was either a fixed-interval or variable-interval schedule. The middle and terminal components were varied among fixed-interval fixed-interval, variable-interval variable-interval, and an interdependent variable-interval variable-interval schedule in which the sum of the durations of the two variable-interval components was always equal to the sum of the fixed-interval fixed-interval components. At issue was whether the response rate in the initial component was controlled by its time to primary reinforcement or by the temporal parameters of the stimulus correlated with the middle terminal link. The fixed-interval initial-link schedule maintained much lower response rates than the variable-interval initial-link schedule regardless of the schedules in the middle and terminal links. Nevertheless, the intervening schedules played some role: With fixed-interval schedules in the initial links, response rates were consistently highest with independent variable-interval schedules in the middle and terminal links and intermediate with the interdependent variable-interval schedules; these initial-link differences were predicted by the response rates in the middle link of the chain. With variable-interval schedules in the initial links, response rates were lowest with the fixed-interval fixed-interval schedules following the initial link and were not systematically different for the two types of variable-interval variable-interval schedules. The results suggest that time to reinforcement itself accounts for little if any variance in initial-link responding.

Fixed-interval and fixed-ratio reinforcement schedules with human subjects

Operant laboratory studies were conducted as part of the regular activities of a psychiatric research ward. This report includes only some early data obtained from the ward staff, not the patients. A multiple schedule having alternating fixed-ratio and fixed-interval components permitted observations of acquisition and maintenance of behavior at low schedule values, transition to and final performance at greater schedule values, and behavioral changes after a limited-hold contingency was added to the fixed-interval. Prior to the added limited-hold, subjects used watches to time the interval, and usually responded only once before obtaining each fixed-interval reinforcement. Short limited-hold values eliminated clock watching and increased fixed-interval responding. Subjects communicated freely with each other, and it was clear that their performances were controlled both by the contingencies and by instructions. Just as clearly, the instructions themselves were controlled by the contingencies. It was concluded that the kinds of verbal control that were responsible for "nonstandard" fixed-interval performances did not require the postulation of any new behavioral principles.

Memory for patterning under a fixed-interval schedule of reinforcement

The present study was an attempt to evaluate rats’ long-term memory for patterning under a fixed-interval schedule of reinforcement. Rats were trained to respond for food under a multiple random-interval fixed-interval schedule of reinforcement. In the presence of one stimulus rats responded under a random-interval 40-sec schedule. In the presence of a second stimulus they responded under a fixed-interval 120-sec schedule, a schedule that engendered a postreinforce-ment pause followed by positively accelerated responding. During retention intervals of 3,9, and 27 days, the rats continued responding under the random-interval schedule but not under the fixed-interval schedule. After the retention interval they were again exposed to the multiple schedule and responding in the fixed-interval component was evaluated for any loss of patterning. No loss of response patterning on the fixed-interval schedule was evident after a 27-day retention interval. The second part of the experiment was an attempt to interfere with the patterning by exposing rats to a random-interval 20-sec schedule in the presence of the stimulus previously associated with the fixed-interval schedule and then later testing for response patterning in the fixed-interval component. A loss of patterning was not evident after 1 to 8 interfering components, but patterning was degraded after 16 and 32 interfering components. The study suggests that rats have good long-term memory for schedule-controlled performance.

Effects of trialkyltins on the schedule-controlled behavior of the pigeon

Male White Carneaux pigeons trained to respond for food under a multiple fixed-ratio fixed-interval schedule of reinforcement were given single injections of trimethyltin (TMT), or triethyltin (TET). A dose of 0.3 mg/kg TMT produced no effect on behavior, while a 1.0 mg/kg dose was a threshold dose and 1.75 mg/kg produced behavioral changes that persisted for months in some birds. TMT produced effects on responding under the multiple schedule at approximately the same doses that produce neuronal damage in the hippocampus and the brain stem of the pigeon. Higher doses given to untrained birds produced signs of extensive neurological damage. A dose of 1.0 mg/kg of TET decreased rates of responding under both schedule components three hours after administration, but behavior usually had recovered by the next day. Doses of 3.0 and 5.6 mg/kg had similar effects, but responding did not recover for several days. Some birds showed significant rate increases, especially under the fixed-interval component several days to several weeks after TET administration. Doses greater than 10 mg/kg TET were lethal. Dose-effect curves for the effects of d-amphetamine, chlorpromazine and morphine on responding under the multiple schedule were determined for some birds before and one month after 1.0 and 1.5 mg/kg of TMT. TMT shifted the dose-effect curve for d-amphetamine to the right, but it did not produce systematic changes in the dose-effect curves for morphine and chlorpromazine.

Behavioral effects of CGS 8216 alone, and in combination with diazepam and pentobarbital in dogs

Beagle dogs (N=3) responded under a multiple fixed-interval (FI) 300 sec, fixed-ratio (FR) 30 schedule of food presentation. The pyrazoloquinoline derivative CGS 8216, given either intravenously (0.01–3.0 mg/kg) or orally (0.1–30.0 mg/kg) had little effect on either the rate or temporal pattern of responding during either component. Both diazepam (0.3 to 17.5 mg/kg, PO) and pentobarbital (0.1–17.5 mg/kg, PO) produced qualitatively similar effects on behavior. Rates of responding during the FI components first increased, then decreased with increasing doses; both drugs produced only dose-related decreases in the rate of responding during the FR components. CGS 8216 antagonized some of the behavioral effects of diazepam; FI and FR response rates returned to baseline, however the effects of diazepam on quarter-life values were not appreciably altered by CGS 8216. The effects of pentobarbital on schedule-controlled responding were not antagonized by CGS 8216. These results indicate CGS 8216 is a selective benzodiazepine antagonist that does not produce benzodiazepine-like behavioral effects.

Effects of chlorpromazine on fixed-ratio responding: modification by fixed-interval discriminative stimuli.

Effects of chlorpromazine (1 to 100 mg/kg) were assessed on two pigeons' responding under various modifications of a multiple schedule of food delivery. During a fixed-interval component, the first response after 5 min produced food; during the subsequent, fixed-ratio component, the 30th response produced food. Modifications of the schedule entailed changes in stimulus conditions imposed during the fixed-ratio component that did not systematically alter characteristics of performance under non-drug conditions. In the first phase of the experiment, distinctive visual stimuli were correlated with each schedule component (conventional multiple schedule); chlorpromazine produced small decreases in fixed-ratio responding (20% at 30 mg/kg). When each response during the fixed-ratio component produced the stimulus correlated with the fixed-interval schedule (fixed-interval discriminative stimulus) for 1.2 s, effects of chlorpromazine were not different from those under the conventional multiple schedule. Chlorpromazine produced greater decreases in fixed-ratio responding (55% at 30 mg/kg) when either the first response of each fixed ratio changed the stimulus correlated with the fixed-ratio schedule to the fixed-interval discriminative stimulus for the remainder of the fixed-ratio component, or when the fixed-interval discriminative stimulus was presented independently of responding according to a matched temporal sequence. When the fixed-interval discriminative stimulus was present continuously during the fixed-ratio component (mixed schedule), chlorpromazine produced even more substantial decreases in fixed-ratio responding (greater than 80% at 30 mg/kg). Effects of chlorpromazine on fixed-interval responding were also modified by the schedules of fixed-interval discriminative stimulus presentation. The effects of chlorpromazine were a joint function of the stimuli prevailing during the multiple schedule and the degree to which responding influenced these stimuli.

BEHAVIORAL CONTRAST IN FIXED‐INTERVAL COMPONENTS: EFFECTS OF EXTINCTION‐COMPONENT DURATION

Seven albino rats were exposed to a multiple schedule of reinforcement in which the two components (fixed interval and extinction) alternated such that a presentation of the extinction component followed each fixed-interval reinforcement. In baseline sessions, the duration of the extinction component was constant and always one-third of the fixed-interval value. Probe sessions contained a probe segment in which the duration of the extinction component was increased; the response rate in fixed-interval components during the probe segment was compared with the response rate in the segments preceding and following the probe. The effect of increasing the duration of the extinction component was studied under three values of fixed interval: 30 s, 120 s, and 18 s, in three successive conditions. Response rate within fixed intervals was a direct function of duration of the extinction component. Pausing at the beginning of the fixed interval decreased as extinction duration increased. These effects were larger and more consistent for the shorter fixed-interval values (18 s and 30 s). These results indicate a functional relation between relative component duration and responding. For the component providing more frequent reinforcement, this could be stated as an inverse relationship between relative component duration and response rate. This relation is similar to findings regarding the ratio of trial and intertrial duration in Pavlovian conditioning procedures, and suggests that behavioral contrast may be related to Pavlovian contingencies underlying the multiple schedule.

Effects of MK-212 (6-chloro-2[1-piperazinyl]pyrazine) on schedule-controlled behavior and their reversal by 5-HT antagonists in the pigeon

The effects of MK-212 (6-chloro-2[l-piperazinyl]pyrazine), a centrally-active 5-hydroxytryptamine (5-HT; serotonin) agonist, were studied alone and in combination with the 5-HT antagonists, methysergide (0.01–0.1 mg/kg), metergoline (0.01–1.0 mg/kg) and ketanserin (0.01–3.0 mg/kg). Pigeons were maintained under a procedure where key pecks were reinforced under a multiple fixed-interval (FI) fixed-ratio (FR) schedule of food presentation. In the fixed-interval component, the first response after 3 min had elapsed, produced food, while in the fixed-ratio component, the thirtieth response was reinforced. The drug MK-212 (0.1–3.0 mg/kg) produced dose-related decreases in response rates under both components of the schedule. In smaller doses of MK-212 (0.3 and 1.0 mg/kg), the decrease in the response rate was greater in the fixed-interval component than in the fixed-ratio component. Small doses of methysergide (0.03 mg/kg) and metergoline (0.1 mg/kg), which had little effect when given alone, partially blocked the effects of MK-212 (1.7 and 3.0 mg/kg) in decreasing rate. Larger doses of these compounds, which sometimes increased the response rate when given alone, resulted in a more complete restoration of response rates when administered with MK-212. Ketanserin, a selective 5-HT 2 antagonist, reversed the effects of MK-212 in some cases, but the patterning of responses remained disturbed. These results demonstrate that MK-212 was able to disrupt a complex behavioral task in the pigeon at doses which caused no other noticeable signs, and that these effects were reversed in a systematic way by serotonin antagonists, known to exert a similar antagonism of the effects of MK-212 on other behavioral responses.

Effects of valproic acid and ethosuximide on the responding of pigeons maintained under a multiple fixed-ratio fixed-interval schedule of food delivery

The effects of valproic acid and ethosuximide were examined in pigeons responding under a multiple Fixed-Ratio 50 Fixed-Inverval 90-sec schedule of food delivery. When given acutely 30 min prior to behavioral testing, both valproic acid (40, 60, 80, 100, and 120 mg/kg) and ethosuximide (40, 60, 80, 100, and 120 mg/kg) produced generally dose-dependent decreases in responding under both the Fixed-Ratio and Fixed-Interval components. Detailed analysis of drug effects on the temporal distribution of responding under the Fixed-Interval failed to reveal rate-dependent effects for either drug. Varying the presession injection interval from 15 to 120 min indicated that both valproic acid and ethosuximide reduced responding to the greatest extent when given 30 or 60 min before behavioral testing. These results indicate that the anticonvulsants valproic acid and ethosuximide similarly affect schedule-controlled responding, although previous studies have revealed the drugs to have different effects under other procedures.

Effects of thyrotropin-releasing hormone (TRH) and MK-771 on behavior of squirrel monkeys controlled by noxious stimuli

The effects of TRH (0.1–30 mg/kg) and an enzyme-resistant analogue, MK-771 (0.1–10 mg/kg), were characterized in squirrel monkeys on responding maintained in the presence of different visual stimuli by a multiple 3-min fixed-interval (FI), 30-response fixed-ratio (FR) schedule of stimulus-shock termination or by a multiple 5-min FI schedule of food or shock presentation. Under the termination schedule, the first response at the end of 3 min in the FI component or the completion of the 30-response requirement in the FR component terminated the visual stimulus in the presence of which shocks occurred (escape schedule). Under the schedule of food or shock presentation, the first response at the end of the 5-min FI produced food in the presence of red stimulus lights or shock in the presence of white lights. TRH and MK-771 produced large, dose-related increases in responding maintained under the FR stimulus-shock termination schedule whereas these peptides produced smaller increases or did not affect responding under the FI schedule. TRH and MK-771 also produced marked increases in responding maintained by shock presentation at doses that did not alter or decreased food-maintained responding in the same subject. Thus, performances maintained by noxious stimuli are uniquely sensitive to the rate-increasing effects of TRH and MK-771. These findings suggest that the behavioral effects of the neuropeptides, TRH and MK-771, can depend on the specific consequences of behavior and, as such, the effects of these substances are determined by many of the same variables that determine the effects of other behaviorally-active drugs.

Modification of drug effects by l-α-acetylmethadol

The effects of drugs on rate of responding by rats under a multiple fixed-ratio fixed-interval schedule of food presentation were studied before and during chronic administration of l-α-acetylmethadol (LAAM). Small doses of methadone, phencyclidine, chlordiazepoxide and pentobarbital increased rates of responding under the fixed-interval component of the schedule. At higher doses, these drugs, as well as LAAM, morphine and haloperidol, decreased rates of responding under both schedule components. Chronic LAAM administration shifted the dose-effect curves for LAAM, morphine, methadone, and to some extent, perhaps pentobarbital, to the right, but did not shift the dose-effect curves to the right for chlordiazepoxide, phencyclidine and haloperidol. The rate-increasing effects of small doses of methadone, phenccylidine, pentobarbital and chlordiazepoxide were attenuated during chronic LAAM administration.

Responding on a multiple schedule of reinforcement as a function of different septal lesions in the rat

The response rates of rats with either control operations or lateral, medial, or complete septal lesions were compared on a multiple fixed-interval (FI)/random-interval (RI) 40-sec schedule of reinforcement in which the rat was required to respond on a different lever for each alternating schedule component. Rats with lateral septal lesions responded at higher rates during the first 8-sec period of the FI component and had poorer response patterning than rats with control operations on the FI 40-sec reinforcement schedule. On the other hand, rats with medial septal lesions responded at higher rates than controls during the RI 40-sec component. Rats with complete septal lesions switched levers more than did controls before the ongoing schedule was completed. The results suggest that the lateral and medial septum have different functional roles mediating responding for food on interval schedules of reinforcement.

Opioid agonist and antagonist behavioural effects of buprenorphine.

1 The agonist and antagonist effects of a range of buprenorphine doses (0.08-20 mg/kg) were studied on the responding of pigeons under a multiple fixed-ratio, fixed-interval schedule of grain presentation. Various doses (0.02-10 mg/kg) of buprenorphine were also tested in pigeons trained to discriminate between injections of 0.05 mg/kg of fentanyl and injections of distilled water. 2 Buprenorphine, over a broad dose range (0.08-5 mg/kg), increased the rates of responding in the fixed-interval component of the multiple schedule and disrupted patterning of responding within the fixed-interval, without affecting fixed-ratio responding even at a dose of 40 mg/kg. The effects of some of the high doses on fixed-interval responding were still evident one and two days after buprenorphine injection. 3 Doses of buprenorphine which produced increases in fixed-interval responding were also effective as antagonists of the behavioural depression produced by 40 mg/kg of morphine, and were discriminated as fentanyl-like by pigeons trained to discriminate between injections of fentanyl and injections of water. 4 These results show that buprenorphine produces marked agonist and antagonist effects over an extremely broad dose range without producing behavioural depressant effects.

Attack induced by second-order schedules of reinforcement

Food-deprived pigeons were exposed to tandem, chain, and brief-stimulus second-order schedules in which the completion of three 80-sec fixed-interval components was followed by food delivery. Two birds attacked a nearby stuffed pigeon shortly after the presentation of either food-paired or food-nonpaired visual stimuli, as well as following food. The third subject exhibited predominantly postfood attack. These results suggest that the locus of schedule-induced attack can be controlled by a stimulus event, whether food delivery or key-color change, that reliably precedes a relatively long period of food unavailability.

Effects of piribedil on schedule-controlled responding of the pigeon

The effects of piribedil were studied in pigeons responding under a multiple fixed-ratio 30-response, fixed-interval 5-minute schedule of food presentation. Piribedil (0.03–10 mg/kg) increased responding under the fixed-interval component to a much greater extent than d-amphetamine (0.3–3 mg/kg) did. The rate-increasing effects of piribedil on fixed-interval responding were attenuated by haloperidol (0.003 and 0.03 mg/kg), α-methyl- p-tyrosine (50, 100 and 200 mg/kg), and tetrabenazine (10 and 30 mg/kg). These drug interactions suggest that piribedil acts as an indirect-acting, dopaminergic agonist to produce its rate-increasing effects on schedule-controlled responding in the pigeon.

Sensitivity of Responding to Simple vs. Complex Contingencies of Reinforcement

Five rats were trained under second-order schedules in which the completion of 10 short fixed intervals (2, 4, or 8 sec) produced food reinforcement, and then to yoked variable-ratio schedules, in which the individual ratios corresponded to the ratios of responses to reinforcement obtained under the second-order schedules. Changes from second-order to yoked variable-ratio schedules resulted in increases both in overall response rate and running rate for all rats. Response rates decreased whenever the second-order schedules were reinstated for all but one rat. Response rates under the second-order schedules were inversely related to the value of the fixed-interval component. Positively accelerated responding was evident within some interrein forcement intervals under the second-order schedules at all three fixed-interval values studied, but this pattern of responding was more pronounced at the higher fixed-interval values. The yoked variable-ratio schedules, by contrast, generated short postreinforcement pauses followed by uniformly high response rates, and no evidence of positively accelerated responding. To the extent that different rates of responding were maintained by the second-order and yoked variable-ratio schedules, responding can be considered sensitive to the temporal contingency imposed by the fixed-interval component of the second-order schedules.

Interaction of methadone and pentobarbital on chained fixed-interval performance in pigeons.

Abstract The effects of methadone, pentobarbital, and their combination were examined in pigeons key pecking under a chained FR 3 (FI 30 sec) schedule of food presentation. The delivery of grain followed the completion of three 30-second fixed-interval components associated with different colored key lights. Intramuscular injections of methadone alone produced small response rate increases at low doses (0.25 and 0.50 mg/kg) and a dose-dependent decrease in key pecking rates at high doses (1.0 and 2.0 mg/kg). Pentobarbital (2, 4, and 8 mg/kg) produced a dose-dependent increase in response rates; 16 mg/kg pentobarbital markedly reduced or abolished responding. Combinations of these doses of methadone and pentobarbital produced increases in key pecking rates greater than the rate increases produced by methadone alone, and in four of the seven subjects, greater than the rate-increasing effects of pentobarbital alone. Changes in overall response rates were a function of changes in pause time (minutes from food delivery to the first key peck) and running response rates (total key pecks divided by session length minus pause time). Responding in the individual FI 30 sec components varied with the dose of methadone; doses greater than 0.25 mg/kg produced a dose-related decrease in key pecking rates in the initial component and small increases in the middle and terminal components. Pentobarbital (2, 4, and 8 mg/kg) produced large dose-related increases in key pecking rates in the initial and middle components. The largest increase in response rate was observed in the middle component after the combination of drugs was administered. Pentobarbital's rate-increasing effect under the chained schedule attenuated the rate-reducing effect of methadone when administered in combination.

THE DELAY‐REDUCTION HYPOTHESIS OF CONDITIONED REINFORCEMENT AND PUNISHMENT: OBSERVING BEHAVIOR

Pigeons responded in an observing-response procedure in which three fixed-interval components alternated. Pecking one response key produced food reinforcement according to a mixed schedule. Pecking the second (observing) key occasionally replaced the mixed-schedule stimulus with the stimulus correlated with the fixed-interval component then in effect. In Experiment 1, observing was best maintained by stimuli correlated with a reduction in mean time to reinforcement. That finding was consistent with the conditioned-reinforcement hypothesis of observing behavior. However, low rates of observing were also maintained by stimuli not representing delay reduction. Experiment 2 assessed the role of sensory reinforcement. It showed that response rate was higher when maintained by stimuli uncorrelated with reinforcement delay than when the stimuli were correlated with a delay increase. This latter result supports a symmetrical version of the conditioned-reinforcement hypothesis that requires suppression by stimuli correlated with an increase in time to reinforcement. The results were inconsistent with hypotheses stressing the reinforcing potency of uncertainty reduction.

Observing Behavior and Information

Pigeons were allowed to peck either of two side keys to produce (observe) a positive or a negative stimulus on a third, middle key. When pecks to one side key resulted in only the positive stimulus signaling fixed-interval 30 sec, and pecks to the other side key likewise resulted only in the negative stimulus signaling extinction 30 sec, the pigeons pecked the positive stimulus key almost exclusively. Two of three pigeons stopped observing when the positive stimulus never occurred. In a second experiment manipulation of the probability of fixed-interval components had a slight effect on observing responses but a larger effect on fixed-interval rate. These results support the inadequacy of an information account of observing behavior.