No evidence tube entrapment distresses rodents in typical empathy tests.

In the first two experiments an empty tube open at one end was placed in different locations. Male hamsters, tested one at a time, tended to stay close to the tube or in it. During the first minute of the first 4 sessions of Experiment 3, the hamster was unrestrained. If it entered the tube, it was locked within the tube. If it did not enter the tube during the first min, it was placed in it, and the tube was locked. Fifteen min later, the tube was opened, and the hamster was unrestrained for a further 20 min. The tube remained open during Session 5. Hamsters spent more time near the tube than predicted by chance and continued to enter the tube although tube-occupancy duration did not differ from chance levels. In Experiment 4, male rats were tested in two groups: rats in one group had been previously trapped in a tube and rats in the other group allowed to freely explore the test space. For the first two min of each of four 20-min sessions, trapped-group subjects were permitted to move about the chamber unless they entered the tube. In that case, they were locked in for the remainder of the session. If, after two min, they did not enter the tube, they were locked in it for the remaining 18 min. Free rats were unrestricted in all sessions. In Session 5, when both groups were permitted to move freely in the chamber, trapped and free rats spent more time in and near the tube than predicted by chance. These data show tube restraint does not seem to distress either hamsters or rats.

Cocaine and heroin interact differently with nondrug reinforcers in a choice situation.

The present study used a rat choice model to test how cocaine or heroin economically interacted with two different nondrug reinforcers along the substitute-to-complement continuum. In Experiment 1, the nondrug alternative was the negative reinforcer timeout-from-avoidance (TOA)-that is, rats could press a lever to obtain a period of safety from footshock. One group of rats chose between cocaine and TOA and another group chose between heroin and TOA. The relative prices of the reinforcers were manipulated across phases while controlling for potential income effects. When cocaine was the reinforcer, rats reacted to price changes by increasing their allocation of behavior to the more expensive option, thereby maintaining relatively proportional intake of cocaine and TOA reinforcers across prices, suggesting these reinforcers were complements here. In contrast, when heroin became relatively cheap, rats increased allocation of income to heroin and decreased allocation of income to TOA, suggesting that heroin substituted for safety. Additionally, rats were willing to accept more footshocks when heroin was easily available. In Experiment 2, the nondrug alternative was saccharin, a positive reinforcer. Heroin and saccharin were complements, but there was no consistent effect of price changes on the allocation of behavior between cocaine and saccharin. As a model of the processes that could be involved in human drug use, these results show that drug-taking behavior depends on the type of drug, the type of nondrug alternative available, and the prices of both. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Purchase task sensitivity to drug and nondrug reinforcers in opioid-agonist treatment patients.

The behavioral economics of substance abuse has been increasingly recognized as a method of determining the value of abused substances for individuals who use those substances. It has been hypothesized that such analyses could serve as a clinical tool and that demand functions can be targeted predictors for the level of intervention necessary. This study evaluated the sensitivity of a demand task in 2 patient groups in a medication assisted treatment program (methadone maintenance), those who had used opioids in the last 2 months and those who had not used opioids in at least 18 months. Demand for 7 drugs and a control was assessed using hypothetical purchase tasks. Participants maintaining long-term abstinence had significantly higher α (sensitivity to price) and lower Q0 (intensity of demand) for heroin than participants who had recently used opioids. Further research is necessary to illustrate if treatment is responsible for this reduction in demand. If so, demand analyses may provide clinical utility as an aid for treatment planning or as a target for treatment.

Rats (Rattus norvegicus) find occupancy of a restraint tube rewarding.

Two experiments evaluated whether rats' occupancy of a restraint tube is reinforcing. In Experiment 1, each rat in the 0-min group moved freely in a chamber where a wall blocked access to a restraint tube. After 10 min the wall was removed, permitting 15 min of chamber access and tube entry. The other 2 groups were locked in the tube for 10 and 20 min respectively before release into the chamber for 15 min. Across sessions, rats locked up for 10 and 20 min entered the tube more frequently than rats in the 0-min group, and during the first 2 sessions rats in the 20-min group stayed in the tube longer than the other groups. Over sessions this difference disappeared. However, for all groups and sessions the mean percentage of session time in the tube exceeded chance expectations. This result suggests tube occupation was reinforcing. In Experiment 2's Phase 1, rats could enter an open tube. On exiting, the tube door closed. A lever press opened the door for the rest of the 1-hr session. In Phase 2, these rats were locked in the tube for 10 min before the door opened. Upon exiting, the door closed. As in Phase 1, a lever press opened the door for the rest of the session. The latency between pressing and tube entry decreased over sessions, indicating that tube entry reinforced lever pressing. These results are difficult to reconcile with accounts of rat empathy based on the thesis that tube restraint distresses occupants.

Heroin choice depends on income level and economy type.

RATIONALE: In a previous study, investigating choice between heroin and a non-drug alternative in animals and reductions in income (i.e., choices/day) caused the percentage of income spent on heroin to progressively decrease. In contrast, another study found that humans with opioid use disorder spent the majority of their income on heroin even though they had little income. Comparison of these two studies suggests that the seemingly conflicting results could be explained by differences in the underlying economy types of the choice alternatives. OBJECTIVE: The present experiment tested the hypothesis that the effect of income changes on choice between heroin and a non-drug alternative depends on economy type. METHODS: Rats chose between heroin and saccharin under three income levels. For the Closed group, the choice session was the only opportunity to obtain these reinforcers. For the Heroin Open group and the Saccharin Open group, choice sessions were followed by 3-h periods of unlimited access to heroin or saccharin, respectively. RESULTS: As income decreased, the Closed and Heroin Open groups, but not the Saccharin Open group, spent an increasingly greater percentage of income on saccharin than on heroin. The Saccharin Open group, compared to the other groups, spent a greater percentage of income on heroin as income decreased. CONCLUSIONS: Results confirm that the effects of income and economy type can interact and this may explain the apparently discrepant results of earlier studies. More generally, findings suggest that situations where heroin choice has little consequence for consumption of non-drug alternatives may promote heroin use.

Opening the cocaine economy by providing within-session access to a cheaper source of cocaine makes demand for it more elastic.

Previous studies found that opening the cocaine economy by providing postsession access to cocaine had no effect on animals' demand for cocaine, whereas postsession access to saccharin or food made demand for these nondrug reinforcers more elastic. It is possible that there was no effect of economy type on cocaine taking in these earlier studies because of the delay to the postsession cocaine in the open economy. The present experiment tested whether forming an open economy by providing additional within-session cocaine, rather than postsession cocaine, would make rats' demand for cocaine more elastic. Saccharin was used as a nondrug comparison reinforcer. Three groups of rats pressed one lever for cocaine and one for saccharin on an ascending series of fixed ratio (FR) schedules where the number of responses required per reinforcer increased from 1 to 48 over sessions. In the open cocaine and open saccharin economy groups, rats had occasional access during the session to a third lever where cocaine or saccharin reinforcers, respectively, were always available on an FR-1 schedule. The main finding was that demand for cocaine was more elastic in the open cocaine economy group than in either of the other groups. Demand for saccharin was more elastic in the open saccharin economy group than in the open cocaine economy group. This study shows that cocaine taking is sensitive to economy type when the additional source of cocaine in an open economy is available close in time to when rats work for cocaine.

The effect of economy type on heroin and saccharin essential value.

According to behavioral economics, reinforcer value should be lower in an open economy than in a closed economy. An animal model was used to determine how economy type affected the value of heroin and saccharin. In a first phase, separate groups of rats worked for heroin or saccharin. The price of these reinforcers increased over sessions. For rats in the open heroin or open saccharin economies, the work period of each session was followed by a postwork period where a cheaper source of heroin or saccharin was available for three hours. For rats in the closed economies, the work period was their only opportunity to obtain the reinforcer. Rats in the open saccharin economy worked less hard to defend consumption of saccharin as price increased than rats in the closed saccharin economy. That is, opening the saccharin economy reduced its essential value. In contrast, economy type had no effect on heroin's essential value. In a second phase, rats were allowed to choose between heroin and saccharin. The majority of rats strongly preferred saccharin over heroin regardless of economy type. The finding that economy type changed the essential value of saccharin, but not heroin, adds to previous findings suggesting that the value of drug reinforcers is unaffected by future drug availability. The difference in effect of economy type on drug versus nondrug reinforcers could be relevant to addiction. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Like chimpanzees (Pan troglodytes), pigeons (Columba livia domestica) match and Nash equilibrate where humans (Homo sapiens) do not.

Martin, Bhui, Bossaerts, Matsuzawa, and Camerer (2014) found that chimpanzee pairs competing in matching-pennies games achieved the Nash equilibrium whereas human pairs did not. They hypothesized this outcome may be due to (a) chimpanzee ecology producing evolutionary changes that give them a cognitive advantage over humans in these games, and (b) humans being disadvantaged because the cognition necessary for optimal game play was traded off in evolution to support language. We provide data relevant to their hypotheses by exposing pairs of pigeons to the same games. Pigeons also achieved the Nash equilibrium, but did so while also conforming with the matching law prediction on concurrent schedules where choice ratios covary with reinforcer ratios. The cumulative effects model, which produces matching on concurrent schedules, also achieved the Nash equilibrium when it was simulated on matching-pennies games. The empirical and simulated compatibility between matching law and Nash equilibrium predictions can be explained in two ways. Choice to concurrent schedules, where matching obtains, and choice in game play, where the Nash equilibrium is achieved, may reflect the operation of a common process in choice (e.g., reinforcer maximization) for which matching and achieving the Nash equilibrium are derivative. Alternatively, if matching in choice is innate as some accounts argue, then achieving the Nash equilibrium may be an epiphenomenon of matching. Regardless, the wide species generality of matching relations in nonhuman choice suggests game play in chimpanzees would not prove advantaged relative to most species in the animal kingdom. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The effect of economy type on demand and preference for cocaine and saccharin in rats.

BACKGROUND: Economy type is an important determinant of reinforcer value. This study investigated the effect of open and closed economies on demand and preference for cocaine and saccharin in rats. METHODS: In the first phase, rats were trained to lever press for cocaine infusions or saccharin. The number of presses required for each reinforcer increased across sessions. Cocaine and saccharin economy type was manipulated over groups by varying post-session availability of these reinforcers. One group of rats had three hours' post-session access to unlimited cocaine (open economy). A second group had three hours' post-session access to unlimited saccharin. A third group had no post-session access to either reinforcer (closed economy). In a second phase, rats in the three conditions could make mutually exclusive choices for cocaine or saccharin. RESULTS: Post-session access to saccharin caused saccharin demand to become more elastic. Post-session access to cocaine had no effect on demand for cocaine but made demand for saccharin more elastic. Results from the choice phase generally paralleled those from the demand phase, the main finding being that post-session saccharin access caused an increase in cocaine preference. CONCLUSIONS: These results show that manipulating economy type can affect cocaine and non-drug reinforcers differently. Opening the saccharin economy decreased saccharin's value. Opening the cocaine economy did not decrease cocaine's value, but instead led to a devaluation of saccharin. These results suggest that cocaine choice may be determined not only by the reinforcers immediately available, but also by those reinforcers' broader contexts of availability.

Does a rat free a trapped rat due to empathy or for sociality?

This report evaluates whether a rat releasing a trapped rat from a restraint tube is better explained as due to its empathic motivation or to the pursuit of social contact. In the first condition, each of six rats chose in an E maze between entering an empty goal box versus entering a goal box where its entrance caused a rat trapped in a restraint tube to be released. Rats preferred the goal box with the trapped rat over the empty goal box. In the second condition, these rats chose between releasing a restraint-tube-trapped rat in one goal box and another rat in the second goal box that was not locked into its restraint tube. Rats showed no preference between alternatives. In the third condition, rats chose between a goal box containing a rat with an open restraint tube and an empty goal box. Rats preferred the rat with the open restraint tube over the empty goal box. These results support attributing the response of releasing a rat from a restraint tube to the reinforcing power of social contact rather than interpreting this response as empathically motivated.

The effect of nicotine pre-exposure on demand for cocaine and sucrose in male rats.

The aim of the present study was to determine how nicotine pre-exposure affects the elasticity of demand for intravenous cocaine and for sucrose pellets in adult male rats. In Experiment 1, demand for cocaine was assessed in rats that had nicotine in their drinking water. Nicotine pre-exposure significantly decreased rats' willingness to defend cocaine consumption as the price (measured as the number of responses per cocaine infusion) increased compared with a control group with no nicotine pre-exposure. That is, nicotine increased the elasticity of demand for cocaine infusions. Experiment 2 repeated the first experiment, but with rats working for sucrose pellets instead of cocaine. Nicotine pre-exposure had no effect on the elasticity of demand for sucrose. This pattern of results suggests that nicotine pre-exposure can reduce the reinforcing effects of cocaine, but not sucrose, in adult male rats.

Heroin and saccharin demand and preference in rats.

BACKGROUND: Several recent studies have investigated the choice between heroin and a non-drug alternative reinforcer in rats. A common finding in these studies is that there are large individual differences in preference, with some rats preferring heroin and some preferring the non-drug alternative. The primary goal of the present study was to determine whether individual differences in how heroin or saccharin is valued, based on demand analysis, predicts choice. METHODS: Rats lever-pressed for heroin infusions and saccharin reinforcers on fixed-ratio schedules. The essential value of each reinforcer was obtained from resulting demand curves. Rats were then trained on a mutually exclusive choice procedure where pressing one lever resulted in heroin and pressing another resulted in saccharin. After seven sessions of increased access to heroin or saccharin, rats were reexposed to the demand and choice procedures. RESULTS: Demand for heroin was more elastic than demand for saccharin (i.e., heroin had lower essential value than saccharin). When allowed to choose, most rats preferred saccharin. The essential value of heroin, but not saccharin, predicted preference. The essential value of both heroin and saccharin increased following a week of increased access to heroin, but similar saccharin exposure had no effect on essential value. Preference was unchanged after increased access to either reinforcer. CONCLUSION: Heroin-preferring rats differed from saccharin-preferring rats in how they valued heroin, but not saccharin. To the extent that choice models addiction-related behavior, these results suggest that overvaluation of opioids specifically, rather than undervaluation of non-drug alternatives, could identify susceptible individuals.

Essential values of cocaine and non-drug alternatives predict the choice between them.

This study investigated the relationship between reinforcer value and choice between cocaine and two non-drug alternative reinforcers in rats. The essential value (EV, a behavioral economic measure based on elasticity of demand) of intravenous cocaine and food (Experiment 1) or saccharin (Experiment 2) was determined in the first phase of each experiment. Food had higher EV than cocaine, whereas the EVs of cocaine and saccharin did not differ. In the second phase of each experiment, rats were allowed to make mutually exclusive choices between cocaine and the non-drug alternative reinforcer. The main findings were that the EV of cocaine was a positive predictor of cocaine preference and the EV of food or saccharin was a negative predictor of cocaine preference. An analysis of within-session patterns of choice behavior revealed sequential dependencies, whereby rats were more likely to choose cocaine on a particular trial after having chosen the non-drug alternative on previous trials. When the time between choices was increased, these sequential dependencies disappeared. The results of these experiments are consistent with the suggestion that addiction-like behavior involves both overvaluation of drug reinforcers and undervaluation of non-drug reinforcers.

Does a rat release a soaked conspecific due to empathy?

In Experiment 1, rats choosing in an E maze preferred to release a rat standing in a pool of water to dry ground over a rat already standing on dry ground. Five additional experiments showed that the choosing rat's preference for releasing the wet rat was maintained by two separable outcomes: (1) the social contact offered by the released rat and (2) the reinforcing value of proximity to a pool of water. These results call into question Sato et al.'s (Anim Cogn 18:1039-1047, 2015) claim to have demonstrated that a rat's releasing of a wet rat to dry ground is empathically motivated.

Scaling reward value with demand curves versus preference tests.

In Experiment 1, six capuchins lifted a weight during a 10-min session to receive a food piece. Across conditions, the weight was increased across six different amounts for three different food types. The number of food pieces obtained as a function of the weight lifted was fitted by a demand equation that is hypothesized to quantify food value. For most subjects, this analysis showed that the three food types differed little in value. In Experiment 2, these monkeys were given pairwise choices among these food types. In 13 of 18 comparisons, preferences at least equaled a 3-to-1 ratio; in seven comparisons, preference was absolute. There was no relation between values based on degree of preference versus values based on the demand equation. When choices in the present report were compared to similar data with these subjects from another study, between-study lability in preference emerged. This outcome contrasts with the finding in demand analysis that test-retest reliability is high. We attribute the unreliability and extreme assignment of value based on preference tests to high substitutability between foods. We suggest use of demand analysis instead of preference tests for studies that compare the values of different foods. A better strategy might be to avoid manipulating value by using different foods. Where possible, value should be manipulated by varying amounts of a single food type because, over an appropriate range, more food is consistently more valuable than less. Such an approach would be immune to problems in between-food substitutability.

Dose and elasticity of demand for self-administered cocaine in rats.

The present experiment tested whether the elasticity of demand for self-administered cocaine in rats is dose-dependent. Subjects lever pressed for three different doses of intravenous cocaine - 0.11, 0.33, and 1.0 mg/kg/infusion - on a demand procedure where the number of lever presses required per infusion increased within a session. The main finding was that demand for the 0.11 mg/kg dose was more elastic than it was for the two larger doses. There was no difference in demand elasticity between the 0.33 and 1.0 mg/kg doses. These results parallel findings previously reported in monkeys. The present study also demonstrated that a within-session procedure can be used to generate reliable demand curves.

Preference pulses and the win-stay, fix-and-sample model of choice.

Two groups of six rats each were trained to respond to two levers for a food reinforcer. One group was trained on concurrent variable-ratio 20 extinction schedules of reinforcement. The second group was trained on a concurrent variable-interval 27-s extinction schedule. In both groups, lever-schedule assignments changed randomly following reinforcement; a light cued the lever providing the next reinforcer. In the next condition, the light cue was removed and reinforcer assignment strictly alternated between levers. The next two conditions redetermined, in order, the first two conditions. Preference pulses, defined as a tendency for relative response rate to decline to the just-reinforced alternative with time since reinforcement, only appeared during the extinction schedule. Although the pulse's functional form was well described by a reinforcer-induction equation, there was a large residual between actual data and a pulse-as-artifact simulation (McLean, Grace, Pitts, & Hughes, 2014) used to discern reinforcer-dependent contributions to pulsing. However, if that simulation was modified to include a win-stay tendency (a propensity to stay on the just-reinforced alternative), the residual was greatly reduced. Additional modifications of the parameter values of the pulse-as-artifact simulation enabled it to accommodate the present results as well as those it originally accommodated. In its revised form, this simulation was used to create a model that describes response runs to the preferred alternative as terminating probabilistically, and runs to the unpreferred alternative as punctate with occasional perseverative response runs. After reinforcement, choices are modeled as returning briefly to the lever location that had been just reinforced. This win-stay propensity is hypothesized as due to reinforcer induction.

The copyist model and the shaping view of reinforcement.

The strengthening view of reinforcement attributes behavior change to changes in the response strength or the value of the reinforcer. In contrast, the shaping view explains behavior change as shaping different response units through differential reinforcement. In this paper, we evaluate how well these two views explain: (1) the response-rate difference between variable-ratio and variable-interval schedules that provide the same reinforcement rate; and (2) the phenomenon of matching in choice. The copyist model (Tanno and Silberberg, 2012) - a shaping-view account - can provided accurate predictions of these phenomena without a strengthening mechanism; however, the model has limitations. It cannot explain the relation between behavior change and stimulus control, reinforcer amount, and reinforcer quality. These relations seem easily explained by a strengthening view. Future work should be directed at a model which combine the strengths of these two types of accounts.