Postreinforcement Pause Research Articles

CJ89-34. A study of negative pressures in oil films and the load carrying mechanism of oil film between two rough surfaces : By Wu Chengwei and Zheng Linqing (Tsinghua University, Beijing, China). Chinese J. Mech. Engng25, No. 3 (Sept., 1989), pp. 19–23

Characterization of functional outcome in animal stroke models is essential to improve preclinical drug screenings. Operant procedures showed promising results for the identification of long-lasting functional deficits. In particular, a suppression of lever-pressing in high ratio schedules has been consistently found in rodent models of ischemic stroke. In the present work, we attempted to replicate these isolated observations, by submitting C57Bl/6J mice to a progressive fixed-ratio schedule of reinforcement three weeks after MCAO or sham surgery. Results showed a significant lever-pressing impairment in the MCAO group. Motivational factors (longer post-reinforcement pause, lesser appeal for food rewards) seemed accountable for the deficit, while motor abilities appeared preserved. These findings resemble fatigue-like states experienced by stroke survivors and may be used as long-term measures of behavioral outcome following experimental stroke.

CJ89-35. A new method to assess the stability in the dynamic performance of machine-tool : By Xiao Youyi and Peng Zemin (Tianjin University, Tianjin, China). Chinese J. Mech. Engng25, No. 3 (Sept., 1989), pp. 24–30

Characterization of functional outcome in animal stroke models is essential to improve preclinical drug screenings. Operant procedures showed promising results for the identification of long-lasting functional deficits. In particular, a suppression of lever-pressing in high ratio schedules has been consistently found in rodent models of ischemic stroke. In the present work, we attempted to replicate these isolated observations, by submitting C57Bl/6J mice to a progressive fixed-ratio schedule of reinforcement three weeks after MCAO or sham surgery. Results showed a significant lever-pressing impairment in the MCAO group. Motivational factors (longer post-reinforcement pause, lesser appeal for food rewards) seemed accountable for the deficit, while motor abilities appeared preserved. These findings resemble fatigue-like states experienced by stroke survivors and may be used as long-term measures of behavioral outcome following experimental stroke.

Effects of interreinforcement interval and food delay on postreinforcement pause of Japanease monkeys

Effects of interreinforcement interval and food delay on postreinforcement pause of Japanease monkeys

CJ89-32. A study of surface formation in cutting process of fine ceramics : By Jin Dongxie (Harbin University of Science and Technology, Harbin, Heilongjiang, China). Chinese J. Mech. Engng25, No. 3 (Sept., 1989), pp. 8–12

Characterization of functional outcome in animal stroke models is essential to improve preclinical drug screenings. Operant procedures showed promising results for the identification of long-lasting functional deficits. In particular, a suppression of lever-pressing in high ratio schedules has been consistently found in rodent models of ischemic stroke. In the present work, we attempted to replicate these isolated observations, by submitting C57Bl/6J mice to a progressive fixed-ratio schedule of reinforcement three weeks after MCAO or sham surgery. Results showed a significant lever-pressing impairment in the MCAO group. Motivational factors (longer post-reinforcement pause, lesser appeal for food rewards) seemed accountable for the deficit, while motor abilities appeared preserved. These findings resemble fatigue-like states experienced by stroke survivors and may be used as long-term measures of behavioral outcome following experimental stroke.

CJ89-31. A study of the criterion for ceramic tool fracture in intermittent turning steel : By Ai Xing and Xia Chuanbo (Shandong Polytechnic University, Jinan, Shandong, China). Chinese J. Mech. Engng25, No. 3 (Sept., 1989), pp. 1–7

Characterization of functional outcome in animal stroke models is essential to improve preclinical drug screenings. Operant procedures showed promising results for the identification of long-lasting functional deficits. In particular, a suppression of lever-pressing in high ratio schedules has been consistently found in rodent models of ischemic stroke. In the present work, we attempted to replicate these isolated observations, by submitting C57Bl/6J mice to a progressive fixed-ratio schedule of reinforcement three weeks after MCAO or sham surgery. Results showed a significant lever-pressing impairment in the MCAO group. Motivational factors (longer post-reinforcement pause, lesser appeal for food rewards) seemed accountable for the deficit, while motor abilities appeared preserved. These findings resemble fatigue-like states experienced by stroke survivors and may be used as long-term measures of behavioral outcome following experimental stroke.

CJ89-33. A new approach to the mechanism of wear particle formation and growth : By Jia Chunde (Shenyang Institute of Technology, Shenyang, Liaonin, China) and J. S. Sheasby (The University of Western Ontario, Canada). Chinese J. Mech. Engng25, No. 3 (Sept., 1989), pp. 13–18

Characterization of functional outcome in animal stroke models is essential to improve preclinical drug screenings. Operant procedures showed promising results for the identification of long-lasting functional deficits. In particular, a suppression of lever-pressing in high ratio schedules has been consistently found in rodent models of ischemic stroke. In the present work, we attempted to replicate these isolated observations, by submitting C57Bl/6J mice to a progressive fixed-ratio schedule of reinforcement three weeks after MCAO or sham surgery. Results showed a significant lever-pressing impairment in the MCAO group. Motivational factors (longer post-reinforcement pause, lesser appeal for food rewards) seemed accountable for the deficit, while motor abilities appeared preserved. These findings resemble fatigue-like states experienced by stroke survivors and may be used as long-term measures of behavioral outcome following experimental stroke.

Performance of Decorticated Rats on Fixed Interval and Fixed Time Schedules.

Rats with neocortex totally removed (decorticates), rats with hippocampal lesions (hippocampals), and their surgical controls, were trained on a fixed interval (FI) 40 s schedule, where the first bar-press response made more than 40 s after a previous reinforcement was rewarded. The decorticates and hippocampals adopted similar patterns of behaviour to the control groups through there were between-group differences in the details of performance. Compared to controls the hippocampals showed shorter post-reinforcement pauses and faster overall rates of responding, whilst the reverse was true of the decorticates. Some of this performance difference in the decorticates was attributed to difficulty in retrieving and consuming solid food reinforcement. The performance of the decorticates and hippocampals, as reflected by the post-reinforcement pause, response distribution and running rate as a function of post-reinforcement pause duration, suggests that timing remains operational in both groups. The differences in response profiles between the two experimental groups, however, indicate that hippocampus and neocortex probably make independent contributions to performance in this situation. The decorticates and their control group were later transferred from the FI to a response-independent fixed time (FT) 40 s schedule. Both groups then returned to the former FI 40 s schedule. The decorticates adjusted their behaviour to the different schedules in the same way as the control animals. The results overall are consistent with previous findings that decortication does not abolish normal patterns of operant learning and extends them to include temporal schedules.

Instructed Human Fixed-Interval Performance: The Effects of the Experimental Setting

Four experimentally naive human subjects were exposed to three fixed-interval (FI) schedules of reinforcement: FI 600 s, FI 300 s, and FI 60 s. The subjects were given instructions specifying the fixed interval based nature of the schedules and the behavior required to obtain points, later exchangeable for money. The experimental setting comprised of three rooms: Room A contained reading material, food snacks, and a variety of nonalcoholic beverages; Room B contained a computer keyboard; and Room C contained a monitor connected to the keyboard in Room B. The subjects were instructed to type “FEED” on the keyboard in Room B and then immediately check the monitor in Room C for the delivery of points. During exposure to the FI 600-s schedule all subjects produced pause-respond local response rates. These patterns persisted when subjects were transferred to the FI 300-s schedule. For a number of sessions during exposure to the FI 300-s schedule Room A was locked. The introduction of these “two-room” sessions decreased response rates and increased the postreinforcement pauses (PRPs) for three subjects. The FI 60-s schedule produced low response rates and extended PRPs for all four subjects. With a return to the FI 600 s, all subjects reverted to the pause-respond pattern. These results emphasize the importance of the experimental setting in human operant studies.

Interpolation of a Single Fixed-Ratio Component in a Baseline of Fixed-Ratio Schedules

A study was conducted in which two birds (pigeons) were trained to respond on a fixed-ratio (FR) 100 baseline, and three birds were trained to respond on a FR 20 baseline. After stable baseline performance, a single FR 10 was interpolated into the FR 100 baselines while a single FR 200 (FR 250 for one bird) was interpolated into the FR 20 baselines. This was called the uncued condition. The same interpolations were replicated in another condition except that a different stimulus was experimentally associated with the interpolated ratio (cued condition). The results showed that the pause following the uncued interpolated ratio was generally the shortest in the session compared to the postreinforcement pauses for the remaining ratios. This effect occurred regardless of the relative size of the interpolated ratio, although it was absent when the interpolated ratio was cued. Moreover, pauses in those ratio components following the uncued interpolated ratio were slightly reduced, suggesting that the interpolation procedure also produced field effects. The results are discussed in terms of their theoretical relevance to variable-ratio schedule performance.

Assessment of the neural substrate for intracranial self-stimulation by the postreinforcement pause technique.

The poststimulation excitability of neurons mediating intracranial self-stimulation (ICSS) was evaluated by the paired-pulse method. Stimulus effectiveness was assessed by the postreinforcement pause (PRP) and by frequency threshold (FT) determinations in 7 rats performing ICSS in the medial forebrain bundle (MFB) and in the ventral tegmental area (VTA). Stimulus effectiveness values were minimal at conditioning-test (C-T) pulse intervals of 0.6 and 0.8 ms for MFB and VTA animals, respectively, because of neuronal refractoriness. Local potential summation could account for the increase in effectiveness at very short C-T intervals, and an additional peak of enhanced effectiveness at a C-T interval of 2.0 ms, perhaps reflecting synaptic events, was observed only in VTA animals with the PRP method. Important advantages of the PRP method were that the C-T interval was the only stimulus parameter that was varied, and the behavioral output of the animal remained relatively constant.

Assessment of the neural substrate for intracranial self-stimulation by the postreinforcement pause technique.

Assessment of the neural substrate for intracranial self-stimulation by the postreinforcement pause technique.

Rapid demand curves for behavioral economics

A method for determining the relationship between food consumption and the price of food (demand function) in behavioral economic experiments is described. Although previous methods have generally required as long as 40 days, the present method can generate a complete demand function within 7 days, and therefore may be more suitable for use in the evaluation of drugs, toxins, and physiological/anatomical interventions. Moreover, measures of circadian rhythmicity, post-reinforcement pause durations, and interresponse times can also be generated. Three experiments tested the stability of the method in a variety of procedural manipulations: repeated exposure to the procedure, increasing versus random daily food price, and size of daily changes in food price. The procedure generated demand functions that were similar to those that require more extended testing, and the demand functions were not generally affected by procedural manipulations. Body weight, which can also affect consumption, generally decreases with increases in the price of food; so this variable should be recorded and used as a covariate in analyzing demand functions. With the exception of circadian rhythmicity, the other measures were stable across procedural variations and showed expected changes as a function of food price: postreinforcement pause durations increased as price increased, but interresponse times did not.

Effects of sublethal doses of ionizing radiation on schedule-controlled performance in rats

Male rats responded under a fixed-ratio (FR) 50 or a fixed-interval (FI) 120 sec schedule of milk delivery. Separate groups were acutely exposed to 0.5, 1.5, 4.5 or 0 (FI only) Gray (Gy) of cobalt-60 gamma radiation 3 times at 43-day intervals. All rats received an acute dose of 6.5 Gy 64 days after the last of these exposures. One-half and 1.5 Gy did not alter FR or FI performance significantly. After 4.5 Gy, no observable changes in performance occurred within 1 hr of exposure. Maximal reductions in FR response rates occurred 24 hr after exposure and recovery followed over the subsequent 72 hr. Postreinforcement pause was increased and running response rate was decreased by 4.5 Gy. Similar effects were found after each 4.5 Gy exposure. In contrast, FI performance (overall response rate, postreinforcement pause, running response rate, index of curvature) was not altered reliably by 4.5 Gy. Both FR and FI response rates were reduced by 6.5 Gy beginning 24 hr after exposure; FR rates tended to be reduced more than FI rates 24–72 hr after exposure. Response rates under both schedules recovered gradually over 7 weeks. The behavioral effects of 6.5 Gy did not vary as a function of irradiation history. In contrast, irradiation history affected survival in that 4 9 rats previously exposed to 4.5 Gy died during weeks 4–5 after 6.5 Gy, whereas there were no deaths in the rats previously exposed to lower doses. Radiogenic disruption of operant performance was dose-related, reversible, noncumulative and dependent on the schedule of reinforcement.

DETERMINANTS OF PAUSING UNDER VARIABLE‐RATIO SCHEDULES: REINFORCER MAGNITUDE, RATIO SIZE, AND SCHEDULE CONFIGURATION

Pigeons pecked a key under two-component multiple variable-ratio schedules that offered 8-s or 2-s access to grain. Phase 1 assessed the effects of differences in reinforcer magnitude on postreinforcement pausing, as a function of ratio size. In Phase 2, postreinforcement pausing and the first five interresponse times in each ratio were measured as a function of differences in reinforcer magnitude under equal variable-ratio schedules consisting of different configurations of individual ratios. Rates were also calculated exclusive of postreinforcement pause times in both phases. The results from Phase 1 showed that as ratio size increased, the differences in pausing educed by unequal reinforcer magnitudes also increased. The results of Phase 2 showed that the effects of reinforcer magnitude on pausing and IRT durations were a function of schedule configuration. Under one configuration, in which the smallest ratio was a fixed-ratio 1, pauses were unaffected by magnitude but the first five interresponse times were affected. Under the other configuration, in which the smallest ratio was a fixed-ratio 7, pauses were affected by reinforcer magnitude but the first five interresponse times were not. The effect of each configuration seemed to be determined by the value of the smallest individual ratio. Rates calculated exclusive of postreinforcement pause times were, in general, directly related to reinforcer magnitude, and the relation was shown to be a function of schedule configuration.

EFFECTS OF MAGNITUDE OF FOOD REINFORCEMENT ON FREE‐OPERANT RESPONSE RATES

In Experiment 1 rats were trained to press a lever on a variable-ratio schedule of food presentation and were then exposed to progressively increasing magnitudes of food reinforcement. Response running rates (rates exclusive of the postreinforcement pause) were found to increase as a function of increasing reinforcement magnitudes. The effect of reinforcement magnitude on response rates inclusive of the postreinforcement pause, however, was less pronounced. Increases in the magnitude of reinforcement were also found to increase the length of the postreinforcement pause. Rats in Experiment 2 were trained to respond on a chained differential-reinforcement-of-low-rate variable-ratio schedule, and were exposed to increasing magnitudes of reinforcement as in Experiment 1. Response running rates increased in the variable-ratio component but decreased in the other component of the schedule. The results are discussed with reference to incentive accounts of reinforcement and the action of reinforcement on the response units generated by the operative contingencies.

A COMPARISON OF RESPONSE PATTERNS ON FIXED‐, VARIABLE‐, AND RANDOM‐RATIO SCHEDULES

The behavior of individual pigeons on fixed-ratio, variable-ratio, and random-ratio schedules was examined. Within each type of ratio schedule the size of the ratio was varied in an irregular sequence. At various ratio sizes (5, 10, 40, 80) no differences were found among overall response rates (postreinforcement pause plus running response rate) as a function of ratio type. This similarity in overall response rates held despite noticeable differences in the microstructure of performance both within and across subjects; the primary performance difference on the three types of ratio schedules was the relatively longer postreinforcement pause duration on the fixed-ratio schedule. We concluded that the gross temporal characteristics of performance determined by the relative weightings of the postreinforcement pause and running response rate were primarily controlled by the type of ratio schedule (fixed, variable, or random), whereas the overall rate of responding was controlled by the size of the ratio.

Measurement of intracranial self-stimulation thresholds using the post-reinforcement pause

A method for measuring the current threshold for intracranial self-stimulation (ICSS) using the post-reinforcement pause (PRP) is described. Rats trained to lever press on a fixed ratio schedule for ICSS in prefrontal cortex, medial forebrain bundle, ventral tegmental area or periaqueductal gray received stimuli of opposite polarity in an alternating fashion. Stimuli of one polarity were sufficient to maintain ICSS responding by themselves (maintaining stimuli). Stimuli of the other polarity were systematically varied in 5–10 μA steps (experimental stimuli). PRPs following both maintaining (Pm) and experimental (Pe) stimuli were measured, and the ratio Pm/Pe was calculated. The PRP threshold was defined as the lowest experimental stimulus current producing PRP ratios significantly less than the ratios produced by all lower current steps. After the PRP threshold for one polarity was determined in 5 daily sessions, the experimental and maintaining stimuli were reversed, and the PRP threshold was measured for the alternate polarity. Rates of ICSS on a continuous reinforcement schedule were subsequently measured at currents around the PRP threshold. Rates increased sharply at PRP threshold, suggesting a correlation between PRP threshold and reinforcement threshold. Similar results were obtained from all four ICSS sites indicating the broad applicability of the PRP threshold method.

INTERMITTENT REINFORCEMENT OF A CONTINUOUS RESPONSE

Six rats were trained with food deliveries contingent upon their pressing a lever and holding it down for either fixed or variable cumulative durations. Fixed-hold requirements ranged from 15 s to 90 s over experimental conditions; variable-hold requirements ranged from 15 s to 120 s. At most long and intermediate values, variable-hold requirements maintained more lever holding than fixed requirements. At the longest hold requirements studied, more lever holding was maintained by variable requirements than by fixed requirements of equivalent mean length for each rat. Postreinforcement-pause duration increased with lever-holding time for both fixed- and variable-hold requirements. At comparable lever-holding times per reinforcer, longer pauses typically were produced by fixed requirements than by variable requirements. Data from this study on the maintenance of responding, temporal response patterns, and postreinforcement pausing are comparable to those obtained with intermittent reinforcement of discrete responses. These findings suggest that the response-reinforcer relation specified by a reinforcement schedule is a fundamental determinant of responding, whether responding consists of discrete units or of continuous activity.

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.

Operant conditioning in the newly hatched quail : Fixed interval performance

Newly hatched quails and adult controls of the species Coturnix coturnix japonica were trained to emit a treadle-pressing response reinforced with food on a Fixed Interval 60 seconds schedule, at a pace of 4 or 5 sessions a day. The young subjects were successfully shaped at the fourth day of life. Although response rates were equivalent in young and adults, Curvature Index values and post-reinforcement pause durations were higher for the adult subjects over a 10-day conditioning period. These differences in the temporal regulation of behavior are discussed in relationship with factors involved in developmental studies.