Environmental enrichment accelerates the acquisition of schedule-induced drinking in rats.

Environmental enrichment (EE) provides an improvement in the housing conditions of experimental animals, such as laboratory rats, with greater physical and social stimulation through toys and company in the home cages. Its use is known to influence performance of experimental protocols, but these effects have not been well determined in the schedule-induced drinking (SID) procedure. The main goal of this study was to investigate the effects of EE on the acquisition of SID in 24 12-week-old male Wistar rats, divided into two groups, a group with EE housed with toys and companions, and a group without enrichment in individual housing conditions without toys (social isolation and no environmental enrichment, INEE). A total of 25 sessions, under a fixed time 30 s food reinforcement schedule and with access to water in the experimental chambers were carried out. Sessions lasted 30 min. The results showed that the EE group developed faster the excessive drinking pattern of SID, and drank to higher levels, than the INEE group. The greater development of SID in the EE group contradicts the view of schedule-induced behavior as linked to stress reduction and better suits with the conception of induction related to positive reinforcement.

Activity-based anorexia alters hypothalamic POMC and orexin populations in male rats.

The objective of this study was to investigate the orexin and POMC populations in the hypothalamic nuclei of male Wistar rats after the activity-based anorexia (ABA) procedure. Four groups were established based on food restriction and activity: activity (A), ABA, diet (D) and control (C). The ABA protocol consisted of free access to a running wheel for a period of 22 h and access to food for 1 h. When the animals in the ABA group reached the ABA criterion, were sacrificed, and their brains were collected and serially sectioned. The free-floating sections were processed for orexin and POMC immunostaining. The number of orexin A-ir cells in the perifornical-dorsomedial-hypothalamus continuum (PFD) and lateral hypothalamus (LH) and the number of POMC-ir cells in the arcuate nucleus (Arc) were estimated. Data on food intake, body weight and wheel turns were also analyzed. The ABA procedure caused a significant decrease in body weight along with a significant increase in activity. Moreover, at the end of the ABA procedure, the number of POMC-ir cells decreased in the Arc in the A group, and significantly more in the ABA group, and the number of orexin A-ir positive cells decreased in the LH in D and ABA groups. The differential decrease in POMC in the ABA group emphasizes the importance of the melanocortin system in the maintenance of ABA, but more research is needed to elucidate the involvement of this peptide in the mechanism that promotes and maintains anorexia nervosa and how increased activity may interact with all these processes.

Chronic ∆-9-tetrahydrocannabinol administration delays acquisition of schedule-induced drinking in rats and retains long-lasting effects.

RATIONALE: Schedule-induced drinking (SID) is a behavioural phenomenon characterized by an excessive and repetitive drinking pattern with a distinctive temporal distribution that has been proposed as a robust and replicable animal model of compulsivity. Despite cannabis currently being the most widely consumed illicit drug, with growing interest in its clinical applications, little is known about the effects of ∆-9-tetrahydrocannabinol (THC) on SID. OBJECTIVES: The effects of chronic and acute THC administration on SID acquisition, maintenance and extinction were studied, as were the effects of such administrations on the distinctive temporal distribution pattern of SID. METHODS: THC (5 mg/kg i.p.), or the corresponding vehicle, was administered to adult Wistar rats for 14 days in a row. Subsequently, THC effects on SID acquisition were tested during 21 sessions using a 1-h fixed-time 60-s food delivery schedule. Acute effects of THC were also evaluated after SID development. Finally, two extinction sessions were conducted to assess behavioural persistence. RESULTS: The results showed that previous chronic THC treatment delayed SID acquisition and altered the distinctive behavioural temporal distribution pattern during sessions. Moreover, acute THC administration after SID development decreased SID performance in animals chronically pre-treated with the drug. No great persistence effects were observed during extinction in animals pre-treated with THC. CONCLUSIONS: These results suggest that chronic THC affects SID development, confirming that it can disrupt learning, possibly causing alterations in time estimation, and also leads to animals being sensitized when they are re-exposed to the drug after long periods without drug exposure.

Assessment of the 'timing' function of schedule-induced behavior on fixed-interval performance.

It has been suggested that schedule-induced behaviors allow organisms to adapt better to temporal regularities of the environment. The main goal of the present study was to observe the effect of schedule-induced drinking (SID) on the performance in fixed-interval (FI) schedules. Rats were exposed to a FI 15-, 30-, or 60-s food reinforcement schedule, and only half of them had access to water in the experimental chamber. Rats with access to water developed SID, which occurred in the first part of the interval, regardless of the FI value, and was followed by an increase in lever pressing rate. There were no substantial differences in the quantitative measures of timing between groups that had or did not have access to water, except for the rats in the FI 15-s group with access to water, who showed longer postreinforcement pauses, possibly attributable to competition between SID and lever pressing. SID did not manifest the scalar property, contrary to lever pressing, but it is proposed that behaviors are displayed serially until the last behavior before the target operant response becomes a discriminative stimulus for that behavior. It is not assumed that the purpose of schedule-induced behaviors is to aid timing, but the development of behavioral patterns might determine the performance of organisms on temporal tasks. Additionally, in some cases competition between responses might exert more control on when the operant behavior occurs than timing. Timing seems to consist in the temporal organization of available behaviors that leads to a specific behavior occurring at a specified time, a single characteristic that typically had come to indicate accurate timing. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

The role of contingency discriminability in suboptimal choice.

Suboptimal choice consists of a preference for an alternative with a lower probability of reinforcement (suboptimal alternative) over another with a higher probability of reinforcement (optimal alternative) when the former has discriminative stimuli that signal in which trials a reinforcer will be delivered and in which trials it will not. Discriminating the contingencies of reinforcement associated with the stimuli of the suboptimal alternative is necessary to produce suboptimal choice, but the impact of different degrees of discriminability has not been systematically studied. The discriminability of the contingencies of reinforcement depends on the difference in the probability of reinforcement of the two stimuli; higher differences yield higher discriminability. Pigeons were exposed to a procedure that presented a choice between two alternatives, each associated with two stimuli. The contingency discriminability of the suboptimal alternative was manipulated across conditions, while the contingency discriminability of the optimal alternative was absent in all conditions. The overall probability of reinforcement of each alternative remained the same throughout the experiment (p = .2 and p = .5 for the suboptimal and optimal alternatives, respectively). The preference for the suboptimal alternative increased as its discriminability increased. There was a positive correlation between discrimination index and preference for the suboptimal alternative. These results highlight the importance of contingency discriminability to generate suboptimal choice.

The irrelevancy of the inter-trial interval in delay-discounting experiments on an animal model of ADHD.

Delay discounting involves choosing between a small, immediate reward, and a larger but delayed one. As the delay between choice and large reward gets longer, people with ADHD tend to become impulsive faster than controls, indicated by a switch in preference from the large to the smaller reward. Choosing the smaller reward when the larger is considered reward maximizing is labeled impulsive behaviour. It is well documented that increased delays between choice and reward affects choice preference in both humans and other animals. Other variables such as the inter-trial interval or trial length are observed to have an effect on human discounting, but their effect on discounting in other animals is largely assumed rather than tested. In the current experiment, we tested this assumption. One group of rats was exposed to increasing delays between choosing the large reward and receiving it, while another group experienced longer inter-trial intervals that were equal in length to the delays in the other group. This ensured that trial length was controlled for in delay discounting, but that the delay function and inter-trial intervals could be manipulated and measured separately. Results showed that while the delay between choice and reward caused impulsive behaviour in rats, the length of the inter-trial interval (and by extension trial length) had no impact on choice behaviour. A follow-up experiment found this to be the case even if the length of the inter-trial interval was signaled with audio cues. These results suggest that rats, and possibly animals in general, are insensitive to time between trials, and therefore cannot easily represent human counterparts on the task.

Static internal representation of dynamic situations reveals time compaction in human cognition.

INTRODUCTION: The human brain has evolved under the constraint of survival in complex dynamic situations. It makes fast and reliable decisions based on internal representations of the environment. Whereas neural mechanisms involved in the internal representation of space are becoming known, entire spatiotemporal cognition remains a challenge. Growing experimental evidence suggests that brain mechanisms devoted to spatial cognition may also participate in spatiotemporal information processing. OBJECTIVES: The time compaction hypothesis postulates that the brain represents both static and dynamic situations as purely static maps. Such an internal reduction of the external complexity allows humans to process time-changing situations in real-time efficiently. According to time compaction, there may be a deep inner similarity between the representation of conventional static and dynamic visual stimuli. Here, we test the hypothesis and report the first experimental evidence of time compaction in humans. METHODS: We engaged human subjects in a discrimination-learning task consisting in the classification of static and dynamic visual stimuli. When there was a hidden correspondence between static and dynamic stimuli due to time compaction, the learning performance was expected to be modulated. We studied such a modulation experimentally and by a computational model. RESULTS: The collected data validated the predicted learning modulation and confirmed that time compaction is a salient cognitive strategy adopted by the human brain to process time-changing situations. Mathematical modelling supported the finding. We also revealed that men are more prone to exploit time compaction in accordance with the context of the hypothesis as a cognitive basis for survival. CONCLUSIONS: The static internal representation of dynamic situations is a human cognitive mechanism involved in decision-making and strategy planning to cope with time-changing environments. The finding opens a new venue to understand how humans efficiently interact with our dynamic world and thrive in nature.

The essential value of the alternatives of the suboptimal choice procedure is different for pigeons and rats.

Suboptimal choice is the preference for a discriminative alternative with low probability of reinforcement, over a non-discriminative alternative with higher probability of reinforcement. Pigeons consistently prefer the discriminative alternative, whereas rats prefer the non-discriminative; the variables accounting for this difference are not yet clear. The economic concepts related to demand curves have been used to calculate the essential value of different types of reinforcers, so they may be useful to compare the value of the alternatives in the suboptimal choice procedure. The goal of this study was to calculate the essential value of each of the alternatives presented in the suboptimal choice procedure to assess if pigeons (Experiment 1) and rats (Experiment 2) value them differently. In both experiments, the fixed ratio requirement in the initial link was increased throughout sessions in order to obtain the demand curve and calculate the essential value by fitting the exponential-demand model. A Bayesian Linear Mixed-Effects Model indicated that pigeons had higher essential values for the discriminative alternative, whereas rats obtained higher essential values for the non-discriminative alternative. These results suggest that preferences in the suboptimal choice procedure are indeed based on the essential value of the alternatives, and provide a new paradigm to study the variables affecting this phenomenon.

Effect of Schedule-Induced Behavior on Responses of Spontaneously Hypertensive and Wistar-Kyoto Rats in a Delay-Discounting Task: A Preliminary Report.

Delay discounting is the loss of the subjective value of an outcome as the time to its delivery increases. It has been suggested that organisms can become more tolerant of this delay when engaging in schedule-induced behaviors. Schedule-induced behaviors are those that develop at a high rate during intermittent reinforcement schedules without the need of arranged contingency to the reinforcer, and they have been considered as a model of compulsivity. There is evidence that relates compulsivity to greater delay discounting. The rate of delay discounting represents how impulsive the subject is, as the rate of discounting increases the higher the impulsivity. Thus, the main purpose of this study was to undertake a preliminary evaluation of whether developing schedule-induced behaviors affects performance in a delay-discounting task, by comparing spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats. The rats were exposed to a task that consisted of presenting the subjects with two levers: one produced a small, immediate food reinforcer while the other one produced a larger, delayed reinforcer. During Condition A, the levers were presented, and a water bottle and a running wheel were available in the conditioning chambers; during Condition B, only the levers were presented. SHR and WKY rats developed schedule-induced behaviors during Condition A and showed no difference in discounting rates, contradicting previous reports. Lick allocation during response-reinforcer delays and the inter-trial interval (ITI) showed, respectively, pre- and post-food distributions. Discounting rates during Condition B (when rats could not engage in schedule-induced behaviors) did not reach statistical significance difference among strains of animals, although it was observed a tendency for WKY to behave more self-controlled. Likewise it was not found any effect of schedule-induced behavior on discounting rates, however, a tendency for WKY rats to behave more impulsive during access to drink and run seems to tentatively support the idea of schedule-induced behavior as a model of compulsivity in those rats, being impulsivity simply defined as an excess in behavior.

Reinforcing and timing properties of water in the schedule-induced drinking situation.

A series of recent studies from our laboratory have added to the preceding literature on the potential role of water (in addition to food) as a positive reinforcer in the schedule-induced drinking situation, thus suggesting that adjunctive behaviors might have motivational properties that make their engagement a preferable alternative. It has also been suggested that adjunctive behaviors serve as a behavioral clock that helps organisms to estimate time, making their engagement motivational, so that they enable more accurate time adjustment under temporal schedules. Here, we review some of these experiments on conditioned reinforcement and concurrent chains, as well as on temporal learning. Data presented in this article suggest that adjunctive behaviors may be a part of the behavior patterns maintained by reinforcement, thus serving towards a better performance in temporal tasks.