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Rodents can be trained to associate different durations with different stimuli (e.g., light/sound). When the associated stimuli are presented together, maximal responding is observed around the average of individual durations (akin to averaging). The current study investigated whether mice can also average independently trained numerosities. Mice were initially trained to make 10 or 20 lever presses on a single (run) lever to obtain a reward and each fixed-ratio schedule was signaled either with an auditory or visual stimulus. Then, mice were trained to press another lever to obtain the reward after they responded on the run lever for the minimum number of presses [Fixed Consecutive Number (FCN)-10 or -20 trials] signaled by the corresponding discriminative stimulus. Following this training, FCN trials with the compound stimulus were introduced to test the counting behavior of mice when they encountered conflicting information regarding the number of responses required to obtain the reward. Our results showed that the numbers of responses on these compound test trials were around the average of the number of responses in FCN-10 and FCN-20 trials particularly when the auditory stimulus was associated with a fewer number of required responses. The counting strategy explained the behavior of the majority of the mice in the FCN-Compound test trials (as opposed to the timing strategy). The number of responses in FCN-Compound trials was accounted for equally well by the arithmetic, geometric, and Bayesian averages of the number of responses observed in FCN-10 and FCN-20 trials.

Previous studies showed that rats and pigeons can count their responses, and the resultant count-based judgments exhibit the scalar property (also known as Weber's Law), a psychophysical property that also characterizes interval-timing behavior. Animals were found to take a nearly normative account of these well-established endogenous uncertainty characteristics in their time-based decision-making. On the other hand, no study has yet tested the implications of scalar property of numerosity representations for reward-rate maximization in count-based decision-making. The current study tested mice on a task that required them to press one lever for a minimum number of times before pressing the second lever to collect the armed reward (fixed consecutive number schedule, FCN). Fewer than necessary number of responses reset the response count without reinforcement, whereas emitting responses at least for the minimum number of times reset the response counter with reinforcement. Each mouse was tested with three different FCN schedules (FCN10, FCN20, FCN40). The number of responses emitted on the first lever before pressing the second lever constituted the main unit of analysis. Our findings for the first time showed that mice count their responses with scalar property. We then defined the reward-rate maximizing numerical decision strategies in this task based on the subject-based estimates of the endogenous counting uncertainty. Our results showed that mice learn to maximize the reward-rate by incorporating the uncertainty in their numerosity judgments into their count-based decisions. Our findings extend the scope of optimal temporal risk-assessment to the domain of count-based decision-making.

The use of gamma-hydroxybutyrate (GHB), a therapeutic agent and recreational drug, has increased since the late 1990s. Researchers have primarily studied GHB's neurochemical, discriminative, and reinforcing effects, but little is known about the drug's effects on learning, memory, or other complex behavioral processes. This study examined the acute and chronic effects of GHB in rats responding under fixed-consecutive-number (FCN) schedules, which assess working memory. Additionally, we examined stimulus control and response effort as modulators of GHB's effects. GHB dose-dependently reduced operant activity and response rates, but tolerance developed to these effects. GHB had no effect on accuracy or efficiency (i.e., working memory). Stimulus control and response effort did not modulate GHB's effects. These results suggest that GHB produced non-selective behavioral disruption but not working memory impairment.

Number discernment is at the heart of task accuracy for laboratory animals performing Fixed Consecutive Number (FCN) operant tasks. Narrow-limit FCN tasks, in particular, are useful for measuring working memory in rat subjects because performance efficacy, which is set up to concord with food delivery, depends on a fairly precise quantification of cues generated by the rat's ongoing behavior. Reported here is a behavioral pharmacology study that utilized a group of overtrained and FCN-schedule-compliant rats injected in a randomized series of testing sessions with different types of N-methyl-D-aspartate (NMDA) receptor modulating drugs. Modifications made to the narrowlimit FCN schedule permitted a simultaneous measure of druginduced compromises in subjects' sensory integrative or motor coordinating capabilities. This highly sensitive model implicated the intrachannel and the glutamate recognition NMDA receptor binding sites as prime mediators of NMDA antagonist associated memory impairments because drugs acting at the mentioned sites lowered counting efficacy without altering sensorimotor function.

The behavioural trait of impulsivity may be made up of different components, including rapid decision making, intolerance to the delay of reward and a tendency to terminate chains of responses prematurely. It has been proposed to measure the last of these in rats using fixed consecutive number (FCN) schedules. The present study uses a modified version of the FCN procedure in which responding was paced by retracting the response lever for short periods between presses. In this way, the experimenter could control the maximum rate of responding. The procedure was made up of two components based on an FCN 8 schedule of food reinforcement. In the Fast component, lever presses were spaced by a minimum of 2 s and in the Slow component by a minimum of 5 s. The average chain length was significantly shorter, and the rats were less efficient in the Slow component. Five drugs were tested on this baseline, imipramine (1.0-10.0 mg/kg), ethanol (300-3000 mg/kg administered PO), haloperidol (0.01-0.1 mg/kg), chlordiazepoxide ( 1.0-10.0 mg/kg) and d-amphetamine (0.2-0.8 mg/kg). All the drugs reduced responding at the highest dose, but imipramine was different from the others in that it increased the average number of responses in the chain and produced a shift in the chain length distribution to the right, possibly reflecting a reduction in impulsivity. The other four drugs reduced chain length at the highest dose, although in the case of ethanol this effect was very small and, unlike the other three drugs, did not result in a shift in the distribution to the left. The paced FCN procedure can differentiate the effects of different drugs on one aspect of impulsivity, and is likely to be a useful procedure for further study of this aspect of behaviour.

The experiment examined how pigeons differentiate response patterns along the dimension of number. Seven pigeons received food after pecking the left key at least N times and then switching to the right key (Mechner’s Fixed Consecutive Number schedule). Parameter N was set according to a percentile schedule, which is a form of automatic shaping. Our aim was twofold: on the empirical side to determine how run length on the left key would evolve under this shaping procedure and how it would change during a subsequent extinction phase; and on the theoretical side to compare the data with the predictions of a theoretical model of response differentiation. Results showed that during shaping, run length on the left key increased and then, for some pigeons, it stabilized, whereas for others pigeons it remained variable. Some pigeons ceased to respond when average run length reached a highvalue. There were substantial within-session trends in run length. In extinction, before the pigeons ceased to respond altogether, they emitted the same distribution of run lengths as during the last sessions of shaping with the exception, in some birds, of a large number of runs of length zero. These results are interpreted at the light of the theoretical model of numerosity differentiation.Keywords: Mathematical Model, Response Numerosity, Percentile Schedule, Shaping, Pigeon, O presente estudo analisa a diferenciação numérica de padrões de resposta. Em uma caixa de Skinner com duas teclas, sete pombos receberam comida após bicarem pelo menos N vezes na tecla esquerda e depois uma vez na tecla direita (programa “Fixed Consecutive Number” de Mechner). Em cada ensaio, o parâmetro N era ajustado por um programa de reforço percentil (uma forma de shaping automático). O estudo teve dois objetivos. Primeiro, determinar como é que varia o tamanho das corridas na tecla da esquerda durante o procedimento de modelagem (shaping) e durante uma fase de extinção que se seguiu. Segundo, comparar os dados obtidos com as previsões de um modelo teórico de diferenciação da resposta. Os resultados mostraram que, durante a modelagem, o tamanho das corridas na tecla esquerda aumentou e depois, para alguns pombos, estabilizou, enquanto para outros pombos permaneceu variável. Alguns pombos pararam de responder quando o tamanho médio da corrida atingiu valores elevados. Observaram-se ainda variações sistemáticas nos tamanhos das corridas no interior de cada sessão como, por exemplo, o aumento do tamanho da corrida ao longo da sessão. Durante a fase de extinção os pombos produziram distribuições de tamanhos de corrida semelhantes às distribuições produzidas durante as últimas sessões de modelagem com exceção, em alguns sujeitos, do elevado número de corridas de tamanho zero. Estes resultados são interpretados à luz do modelo teórico de diferenciação numérica das respostas. Palavras-chave: Modelo matemático, numerosidade, esquema percentil, modelagem, pombo

The present experiment was designed to investigate whether or not response rate differences between male and female Wistar rats observed in many different experimental procedures could be attributed to sex differences in behavioral perseverance, as has been suggested by the results of previous experiments. Male and female Wistar rats were thus exposed to different fixed-consecutive-number schedules of reinforcement. Fixed-consecutive-number schedules require subjects to emit a specified number of responses on one (work) lever, before a response on another (food) lever results in the presentation of reinforcement. The response requirement on the work lever was manipulated in different experimental conditions. Subjects had to emit between 3 and 7, 8 and 12 or 13 and 17 responses on the work lever before a response on the food lever produced reinforcement. When subjects emitted fewer or more than the required number of responses on the work lever, a 5-s time-out period was presented. Males responded at higher rates than females during all experimental conditions; response rates of males and females increased as the response requirement on the work lever was increased. Sex differences in response efficiency were not observed, but males seemed to reach final response efficiency faster than females. Response efficiency decreased as the response requirement on the work lever was increased. Error analysis showed that both males and females made more errors by not producing enough responses on the work lever than by producing too many. However, males were more likely than females to emit more responses than the requirement on the work lever, while females were more likely than males not to produce enough responses on the work lever.

Background Attention-deficit/hyperactivity disorder (ADHD) is characterized by a pattern of inattention, hyperactivity, and impulsivity that is cross-situational, persistent, and produces social and academic impairment. Research has shown that reinforcement processes are altered in ADHD. The dynamic developmental theory has suggested that a steepened delay-of-reinforcement gradient and deficient extinction of behavior produce behavioral symptoms of ADHD and increased behavioral variability. Method The present study investigated behavioral variability and elimination of non-target responses during acquisition in an animal model of ADHD, the spontaneously hypertensive rat (SHR), using Wistar Kyoto (WKY) rats as controls. The study also aimed at providing a novel approach to measuring delay-of-reinforcement gradients in the SHR and the WKY strains. The animals were tested in a modified operant chamber presenting 20 response alternatives. Nose pokes in a target hole produced water according to fixed interval (FI) schedules of reinforcement, while nose pokes in the remaining 19 holes either had no consequences or produced a sound or a short flickering of the houselight. The stimulus-producing holes were included to test whether light and sound act as sensory reinforcers in SHR. Data from the first six sessions testing FI 1 s were used for calculation of the initial distribution of responses. Additionally, Euclidean distance (measured from the center of each hole to the center of the target hole) and entropy (a measure of variability) were also calculated. Delay-of-reinforcement gradients were calculated across sessions by dividing the fixed interval into epochs and determining how much reinforcement of responses in one epoch contributed to responding in the next interval. Results Over the initial six sessions, behavior became clustered around the target hole. There was greater initial variability in SHR behavior, and slower elimination of inefficient responses compared to the WKY. There was little or no differential use of the stimulus-producing holes by either strain. For SHR, the reach of reinforcement (the delay-of-reinforcement gradient) was restricted to the preceding one second, whereas for WKY it extended about four times as far. Conclusion The present findings support previous studies showing increased behavioral variability in SHR relative to WKY controls. A possibly related phenomenon may be the slowed elimination of non-operant nose pokes in SHR observed in the present study. The findings provide support for a steepened delay-of-reinforcement gradient in SHR as suggested in the dynamic developmental theory of ADHD. Altered reinforcement processes characterized by a steeper and shorter delay-of-reinforcement gradient may define an ADHD endophenotype.

The effects of administering and withdrawing cocaine (0.3, 1, 3, and 10 mg/kg) were evaluated in pigeons responding under a fixed-consecutive-number schedule of food presentation with (FCN-S(D)) and without (FCN) an external discriminative stimulus. Under both schedules, acute administrations of 10 mg/kg reduced accuracy (per cent reinforced runs) and lower doses had no systematic effect. Both 3 and 10 mg/kg doses reduced response rates under the FCN schedule, but only the 10 mg/kg dose did so under the FCN-S(D) schedule. With chronic exposure to increasing doses (0.3, 1, 3, and 10 mg/kg), tolerance developed to the rate- and accuracy-decreasing effects of 10 mg/kg under both schedules. Abrupt withdrawal from chronic cocaine (10.0 mg/kg) did not disrupt performance under either schedule. This indicates that behavioral dependence did not occur in the present study.

Male and female Wistar rats were trained on a fixed-consecutive-number schedule in which a response on a food lever was followed by the presentation of reinforcement when at least three, but not more than seven responses had been completed on a work lever. Subjects were treated with different doses of the centrally acting cholinergic antagonist scopolamine hydrobromide or the more peripherally active cholinergic antagonist scopolamine methylbromide (0.08, 0.16 or 0.32 mg/ml/kg) once behavior had stabilized. Scopolamine hydrobromide and scopolamine methylbromide dose-dependently decreased response rates in males and females. Scopolamine methylbromide decreased response rates more than equivalent doses of scopolamine hydrobromide and the rate-suppressant effects of both drugs were more marked in males than in females. Scopolamine hydrobromide dose-dependently decreased response accuracy, but differences between males and females were not observed. Response accuracy also decreased after scopolamine methylbromide, but did not vary as a function of the dose of the drug. The decrease in response accuracy induced by both drugs was attributable to an increase in the percentage of trials with a premature switch from the work lever to the food lever. Both scopolamine hydrobromide and scopolamine methylbromide dose-dependently increased the number of premature switches. Differences between males and females were not observed. Administration of scopolamine hydrobromide and scopolamine methylbromide also decreased the number of obtained reinforcers in a dose-dependent manner. Females obtained significantly fewer reinforcers than males, while scopolamine methylbromide affected the number of obtained reinforcers to a larger extent than scopolamine hydrobromide.

Two procedures were used in an investigation of the effects of deprivation upon counting and timing. Under the first procedure, fixed minimum interval (FMI), the rat received liquid reinforcement every time it pressed bar B after having waited a minimum of 5 sec following a press on bar A. Under the second procedure, fixed consecutive number (FCN), reinforcement was delivered every time the rat pressed bar B following a run of at least four consecutive responses on bar A. Water deprivation was varied over a set of values ranging from 4 to 56 hr. Deprivation had almost no effect on the waiting time in the FMI procedure, or on the number of responses per run in the FCN procedure. With both procedures, increasing deprivation shortened the pause between reinforcement and the next response. In the FCN procedure, the speed with which the runs were executed increased with increasing deprivation, although the number of responses in these runs was relatively unaffected.

The effects of the neuroleptic pimozide, a specific dopamine receptor blocker, on behavior maintained under different degrees of stimulus control was examined by using a fixed consecutive number (FCN) schedule of reinforcement with pigeons. This schedule requires that at least eight consecutive responses be made on one key (work key) before a response on a second key (reinforcement key) will be reinforced. For half the birds no change in external stimuli accompanied the eighth response (FCN-8) while for the other half the color of the work key changed from white to red after the eighth peck (FCN-SD). Both schedules resulted in equal rates of baseline responding. Four doses of pimozide (vehicle, 0.1, 0.3, 0.5 mg/kg) were administered in a Latin Square sequence after baseline responding was stable. Similar pimozide-induced decreases in responding were observed in both conditions. However, pimozide selectively altered response patterns under the FCN-8 condition. The failure of the FCN-SD procedure to display a similar effect demonstrated that the use of salient exteroceptive stimuli can modulate behavioral deficits induced by pimozide. This conclusion has important implications for theories hypothesizing that dopamine subserves reward processes.

The effects of the antiepilepsy drugs methsuximide and mephenytoin were examined in pigeons responding under a fixed-consecutive-number (FCN) schedule with and without an added external discriminative stimulus. On this schedule, food was delivered whenever subjects responded between 8 and 12 times on one response key (work key), and then responded once on a second response key (reinforcement key). Under one variant of the FCN schedule (FCN 8-SD), an external discriminative stimulus signalled completion of the response requirement on the work key; no such stimulus change occurred under the other (FCN 8) schedule. The two FCN schedules (with an without stimulus change) alternated at 5-min intervals within each session for all subjects. Methsuximide (25–200 mg/kg) and mephenytoin (40–160 mg/kg) produced generally dose-dependent decreases in percentage of reinforced response runs and rate of responding. The magnitudes of these effects were comparable under both variants of the FCN schedule.

The effects of the anticonvulsant drugs clonazepam and ethosuximide were examined in pigeons performing under a fixed-consecutive-number schedule with and without an added external discriminative stimulus. Under these schedules, food was delivered whenever subjects responded between and 8 and 12 times on one response key (work key), and then responded once on a second response key (reinforcement key). For one group, an external discriminative stimulus signalled completion of the response requirement on the work key, while no stimulus change was programmed for the other group. Clonazepam (0.06–0.75 mg/kg) produced dose-dependent decreases in percentage of reinforced runs and rate of responding for both groups. The magnitude of the accuracy-decreasing effect was generally greater in the group without the external discriminative stimulus. For this group, the higher doses of clonazepam produced pronounced increases in switching to the reinforcement key before completing the minimum requirement of eight consecutive responses on the work key. No consistent patterns of errors were evident for the subjects with the added external discriminative stimulus. Although ethosuximide (20–160 mg/kg) produced dose-dependent decreases in rate of responding, it had little effect on the percentage of reinforced runs or the run length distributions. These findings are consistent with previous reports indicating that clonazepam, but not ethosuximide, substantially disrupts performance under operant tasks requiring conditional discriminations. These data also suggest that the addition of an external discrimination stimulus attenuates the disruptive behavioral effects of clonazepam.

Behavior that is strongly controlled by environmental stimuli is less susceptible to disruption by certain chemicals than is such behavior not under strong external control. To determine whether toluene's effects can also be minimized by environmental stimuli, two varieties of a fixed consecutive number schedule were studied. With one, a lever press response was reinforced with milk only if preceded by a minimum of eight consecutive responses on a second lever, no cues indicating that the minimum number had been reached. With the other, a combination of lights and a tone served as a discriminative stimulus signaling the completion of the minimum response number. In an experiment studying these schedules separately, rats were exposed to toluene concentrations up to 3000 ppm for 4-hr periods immediately before their performance was tested. Toluene reduced the accuracy of both types of behavior in a concentration-related fashion. Clear differential effects occurred, with the signaled behavior, i.e., that under stronger stimulus control, showing less disruption by toluene. Similar results were produced after 2-hr exposures with a multiple schedule in which the signaled and unsignaled performances alternated within a single session. Response rate changes were observed at 560 ppm, but changes in rate were independent of effects on the accuracy of performance. The EC50 for significant behavior disruption was 1081 ppm for the unsignaled component of the multiple schedule; the EC10 was 480 ppm. No performance disruption was observed in the signaled component below 1780 ppm. The finding of differential sensitivity could be useful in guiding the development of more sensitive tests of performance impairment.

Four rats were trained under a fixed-consecutive-number (FCN) schedule to make sequences of 20 or more consecutive responses on one lever followed by a single response on a second lever. When performance was stable, they were exposed to 200, 400, and 600 parts-per-million (PPM) carbon monoxide (CO) for either 30 or 60 min before and during a 45-min session. Decreases in response rate at CO levels as low as 200 ppm were due to both decreased local response rate and extended pauses. A lowered percentage of reinforcement, due to decreases in response sequence length, was also found at CO levels as low as 200 ppm. This decreased sequence length may reflect effects of CO on response rate, or a disruption of discriminative aspects of FCN schedule performance.