Reward Strength Research Articles

The reputation-based reward mechanism promotes the evolution of fairness

In real life, a good reputation generally brings positive returns to individuals. For example, merchants with numerous good reviews usually gain higher profits. Considering this in the ultimatum game, we propose a reputation-based reward mechanism to investigate the evolution of fairness. Specifically, individuals' reputations evolve dynamically based on the outcomes of games. At the same time, we set a reputation threshold in the population. When individuals' reputations exceed the reputation threshold, they are considered excellent. Otherwise, they are ordinary. The excellent individuals can receive extra rewards compared to the ordinary ones. Finally, individuals' total payoffs determine their fitness within the population. Based on these settings, this paper mainly explores how reputation threshold, weight factor and reward strength affect the evolution of fairness. Through a series of simulations, the reputation-based rewards mechanism is proved to effectively promote the fairness in the population. To be specific, we find that higher reputation thresholds and smaller values of weight factor significantly enhance the promotion effect of reward on fairness. Simultaneously, there is a specific correspondence between the reputation threshold and the weight factor. When reward strength is fixed, for different reputation thresholds, the optimal value of weight factor to achieve maximum fairness levels also varies. Additionally, increasing reward strength can significantly promote fairness.

Sources of Organizational Power among Administrators Working in the Education Directorates at Zarqa Governorate /Jordan

The study aimed to identify the sources of organizational power of administrators working in the directorates of education in Zarqa Governorate / Jordan and the impact of the variables (gender, academic qualification, job title and experience) on that. The study sample consisted of (218) employees. To achieve the aim of the study a questionnaire was developed consisted of (52) items distributed on six domains: official, reward, experience, reference, punishment and information). Validity and reliability of the tool were verified. The results of the study showed that the degree of estimation of the practice of organizational power sources among administrators working in the directorates of education in Zarqa Governorate / Jordan was medium, and the fields were ranked in descending order, respectively (the domain of experience, the domain of formality, the domain of information, the domain of reference, the domain of reward and the domain of punishment). The results also showed that there were statistically significant differences at the level of significance (α ≤ 0.05) due to job title variable, on the domains (reward strength, experience strength, reference strength, and information strength) and overall score, and the differences were in favor of the department member’s name. There were no differences in the impact of the job title on the rest of the fields. The results showed that there were no statistically significant differences at the level of significance (α ≤ 0.05) due to the variables of gender, educational qualification and years of experience. In light of the results, the researchers recommended a set of recommendations, the most important of which are: Strengthening the practice of the source of expertise based on professional reference by increasing the degree of awareness of the requirements of the job role.

The priming effect of rewarding brain stimulation in rats depends on both the cost and strength of reward but survives blockade of D2-like dopamine receptors.

Receipt of an intense reward boosts motivation to work for more of that reward. This phenomenon is called the priming effect of rewards. Using a novel measurement method, we show that the priming effect of rewarding electrical brain stimulation depends on the cost, as well as on the strength, of the anticipated reward. Previous research on the priming effect of electrical brain stimulation utilized a runway paradigm in which running speed serves as the measure of motivation. In the present study, the measure of motivation was the vigour with which rats executed a two-lever response chain, in a standard operant-conditioning chamber, to earn rewarding electrical stimulation of the lateral hypothalamus. In a second experiment, we introduced a modification that entails self-administered priming stimulation and alternating blocks of primed and unprimed trials. Reliable, consistent priming effects of substantial magnitude were obtained in the modified paradigm, which is closely analogous to the runway paradigm. In a third experiment, the modified paradigm served to assess the dependence of the priming effect on dopamine D2-like receptors. The priming effect proved resilient to the effect of eticlopride, a selective D2-like receptor antagonist. These results are discussed within the framework of a new model of brain reward circuitry in which non-dopaminergic medial forebrain bundle fibers and dopamine axons provide parallel inputs to the final common paths for reward and incentive motivation.

Coevolutionary dynamics of population and institutional rewards in public goods games

In social dilemmas, individuals face a conflict between their own self-interest and the collective interest of the group. The provision of reward has been shown to be an effective means to drive cooperation in such situations. However, previous research has often made the idealized assumption that rewards are constant and do not change in response to changes in the game environment. In this paper, we introduce reward into the public goods game and develop a coevolutionary game model in which the strength of reward is adaptively adjusted according to the population state. Specifically, we assume that decreasing levels of cooperation lead to an increase in reward strength, while increasing levels of cooperation result in a decrease in reward strength. By investigating coevolutionary dynamics between population state and reward systems, we find that interior stable coexistence state can emerge in our model, where the levels of cooperation and reward strength remain at constant levels. In addition, we also reveal that the emergence of a full cooperation state only requires a minimal level of reward strength. Our study highlights the potential of adaptive feedback reward as a tool for achieving long-term stability and sustainability in social dilemmas.

Tryptophan and Substance Abuse: Mechanisms and Impact.

Addiction, the continuous misuse of addictive material, causes long-term dysfunction in the neurological system. It substantially affects the control strength of reward, memory, and motivation. Addictive substances (alcohol, marijuana, caffeine, heroin, methamphetamine (METH), and nicotine) are highly active central nervous stimulants. Addiction leads to severe health issues, including cardiovascular diseases, serious infections, and pulmonary/dental diseases. Drug dependence may result in unfavorable cognitive impairments that can continue during abstinence and negatively influence recovery performance. Although addiction is a critical global health challenge with numerous consequences and complications, currently, there are no efficient options for treating drug addiction, particularly METH. Currently, novel treatment approaches such as psychological contingency management, cognitive behavioral therapy, and motivational enhancement strategies are of great interest. Herein, we evaluate the devastating impacts of different addictive substances/drugs on users' mental health and the role of tryptophan in alleviating unfavorable side effects. The tryptophan metabolites in the mammalian brain and their potential to treat compulsive abuse of addictive substances are investigated by assessing the functional effects of addictive substances on tryptophan. Future perspectives on developing promising modalities to treat addiction and the role of tryptophan and its metabolites to alleviate drug dependency are discussed.

How “punishing evil and promoting good” promotes cooperation in social dilemma

In this paper, based on the social dilemma model, we introduce the punishing evil and promoting good strategy, whose basic strategy is to cooperate, while to obtain benefits at the cost of payment. Specifically, when the person who punishes evil and promotes good plays a game with the cooperator, his contributions will bring the same benefits to both parties, reflecting the promoting good. However, when the person who punishes evil and promotes good plays a game with the defector, making the benefit of the defector loss and become his own benefit, reflecting the punishing evil. The results show that when only the role of punishing evil is considered, increasing punishment strength can easily make those punishing evil and promoting good and ordinary cooperators appear. But only increasing the punishment is not enough to weed out the defectors. When only the effect of promoting good is considered, under a smaller temptation to defection, the increase of the reward strength can transform the system from a full defection state to a full cooperation state. Whereas when the temptation is greater, the increase in the reward is not enough for the cooperator to survive and only defectors exist in the system at this time. In addition, there exist combinations of minimum values of punishment and reward that bring the system to a defector-free state. In conclusion, our study finds effective intervals for promoting the development of those who punish evil and promote good and ordinary cooperators, respectively.

A Game Theoretic Model of Adversaries and Media Manipulation

A model is developed for two players exerting media manipulation efforts to support each of two actors who interact controversially. Early evidence may support one actor, while the full evidence emerging later may support the other actor. Exerting effort when the full evidence exceeds (falls short off) the early evidence is rewarded (punished) with lower (higher) unit effort cost. Properties and simulations are presented to illustrate the players’ strategic challenges when altering eight model parameters, i.e., a player’s unit effort cost, stake in the interaction, proportionality parameter scaling the strength of reward or punishment, time discount parameter, early evidence, full evidence, contest intensity, and evidence ratio intensity. Realizing the logic of the model may aid understanding on how to handle the difference between early and full evidence of controversies, in which players have an ideological stake.

Organizational Strength and its Role in Enhancing Competitive Advantage "

The purpose of this research is to identify the organizational role of the four types of organizational strengths such as: Sharia strength, reward power, strength of expertise, information power in enhancing the competitive advantage of the working managers and their assistants, A questionnaire was designed for the research variables to collect the data, consisting of (21) paragraphs representing the organizational power paragraphs, and (10) paragraphs representing the competitive advantage clauses. The questionnaire outputs (60) were analyzed and processed statistically and presented through the Statistical Package (SPSS). Based on the test of the research plan and its hypotheses, the research reached the following:
 
 There is a significant correlation between organizational strength and competitive advantage at the macro level.
 There is a significant correlation between the types of organizational power represented by (legitimate strength, reward power, strength of experience, information power) and competitive advantage.
 The existence of a significant influence of the organizational power in the competitive advantage at the macro level.
 The existence of a relationship of significant influence to the types of organizational power represented by (the legitimate force, the strength of reward, the strength of experience, the power of information) in the competitive advantage.
 
 In the light of the conclusions, a number of proposals were put forward, the most important of which was the promotion of awareness within the university at all levels of management of the importance and types of organizational power (legitimate power, reward power, the power of expertise, the power of information) to encourage workers and generate creative ideas and their role. In enhancing the competitive advantage. And the need to work to consolidate the meaning and the positive concept of force in order to unite efforts to benefit from the use of organizational power and the role they play in achieving the objectives of the University.
 Keywords: Strength / Organizational Strength / Competitive Advantage

Crayfish Self-Administer Amphetamine in a Spatially Contingent Task.

Natural reward is an essential element of any organism’s ability to adapt to environmental variation. Its underlying circuits and mechanisms guide the learning process as they help associate an event, or cue, with the perception of an outcome’s value. More generally, natural reward serves as the fundamental generator of all motivated behavior. Addictive plant alkaloids are able to activate this circuitry in taxa ranging from planaria to humans. With modularly organized nervous systems and confirmed vulnerabilities to human drugs of abuse, crayfish have recently emerged as a compelling model for the study of the addiction cycle, including psychostimulant effects, sensitization, withdrawal, reinstatement, and drug reward in conditioned place preference paradigms. Here we extend this work with the demonstration of a spatially contingent, operant drug self-administration paradigm for amphetamine. When the animal enters a quadrant of the arena with a particular textured substrate, a computer-based control system delivers amphetamine through an indwelling fine-bore cannula. Resulting reward strength, dose-response, and the time course of operant conditioning were assessed. Individuals experiencing the drug contingent on their behavior, displayed enhanced rates of operant responses compared to that of their yoked (non-contingent) counterparts. Application of amphetamine near the supra-esophageal ganglion elicited stronger and more robust increases in operant responding than did systemic infusions. This work demonstrates automated implementation of a spatially contingent self-administration paradigm in crayfish, which provides a powerful tool to explore comparative perspectives in drug-sensitive reward, the mechanisms of learning underlying the addictive cycle, and phylogenetically conserved vulnerabilities to psychostimulant compounds.

Optimizing reproducibility of operant testing through reinforcer standardization: identification of key nutritional constituents determining reward strength in touchscreens

Reliable and reproducible assessment of animal learning and behavior is a central aim of basic and translational neuroscience research. Recent developments in automated operant chamber technology have led to the possibility of universal standard protocols, in addition to increased translational potential, reliability and accuracy. However, the impact of regional and national differences in the supplies of available reinforcers in this system on behavioural performance and inter-laboratory variability is an unknown and at present uncontrolled variable. Therefore, we aimed to identify which constituent(s) of the reward determines reinforcer strength to enable improved standardization of this parameter across laboratories. Male C57BL/6 mice were examined in the touchscreen-based fixed ratio (FR) and progressive ratio (PR) schedules, reinforced with different kinds of milk-based reinforcers to directly compare the incentive values of plain milk (PM, high-calorie: high-fat/low-sugar), strawberry-flavored milk (SM, high-calorie: low-fat/high-sugar), and semi-skimmed low-fat milk (LM, low-calorie: low-fat/low-sugar) on the basis of differences in caloric content, sugar/fat content, and flavor. Use of a higher caloric content reward was effective in increasing operant training acquisition rate. Total trial number completed in FR and breakpoint in PR were higher using the two isocaloric milk products (PM and SM) than the lower caloric LM, with comparable outcomes between PM and SM conditions, suggesting that total caloric content determines reward strength. Analysis of within-session changes in response rate revealed that overall outputs in FR and PR primarily depend on the response rate at the initial phase of a session, which itself was dependent on reinforcer caloric content. Interestingly, the rate of satiation, indicated by decay in response rate within a FR session, was highest when reinforced with SM, suggesting a rapid satiating effect of sugar. The key contribution of reward caloric content to operant performance was confirmed in a multi-laboratory study using the touchscreen 5-choice serial reaction time task (5-CSRTT) reinforced by two isocaloric milk-based liquid rewards with different countries of origin, which yielded consistent performance parameters across sites. Our results indicate that milk-based liquid reinforcer standardization can be facilitated by matching caloric content across laboratories despite regional or national differences in other non-caloric aspects of the reinforcers.

William L Woolverton.

Dr William L Woolverton, Billy S Guyton Distinguished Professor and Vice Chair for Research in the Department of Psychiatry and Human Behavior at the University of Mississippi Medical Center died after a brief illness at the age of 62 on 13 June 2013. Professor Woolverton, a member of ACNP, was a leading scientist and educator in the behavioral pharmacology of drugs of abuse. An Alabama native, Bill attended the University of the South in Sewanee, Tennessee, graduating Phi Beta Kappa in 1972. He did graduate work at the University of Chicago, studying pharmacology under the mentorship of Dr Charles R Schuster, graduating with a PhD in 1977. Although Bill received his formal training as a pharmacologist, he was strongly influenced by the behavioral sciences, conducting his doctoral research in the Psychiatry Department with a psychologist. Thus, many of Bill's major scientific contributions were on the behavioral determinants of the abuse-related effects of drugs. He did most of his research using nonhuman primates. From 1977 to 1980 Bill did postdoctoral work at Virginia Commonwealth University primarily in the laboratories of Dr Robert Balster in the Department of Pharmacology and Toxicology. Bill wanted to understand better how the reinforcing effects of drugs were altered by the context of their availability. This led him to a series of complex choice studies in which rhesus monkeys were given opportunities to select cocaine or food reinforcement and how various manipulations, such as concurrent drug treatment, altered this choice behavior. The results of this line of work convinced Bill that drug-taking behavior was not “impulsive” and “out of control” as has often been proposed, but rather is directly determined by the context of its availability, providing a nuanced understanding of drug–behavior interactions. In 1980, Bill returned to the University of Chicago as an Assistant Professor in the Department of Psychiatry in the research group headed by Charles R Schuster. When Bob Schuster left to become NIDA Director in 1986, Bill replaced him as the Director of the Drug Abuse Research Center. While in Chicago, Bill showed that activation of both D1-like and D2-like dopamine receptors were involved in the reinforcing effects of cocaine. He also continued his studies with drug choice and drug–food choice paradigms with the purpose of studying the reinforcing efficacy of stimulant drug administration. He utilized these models for studying potential pharmacotherapies that might reduce the strength of cocaine reward, but of equal importance, he found that he could reduce cocaine-reinforced behavior just as easily by manipulating environmental variables, such as the value of alternative reinforcers. This work is consistent with the view that combined pharmacotherapies and behavioral therapies may offer the best hope for stimulant abuse treatment. In 1993, Bill was recruited to the University of Mississippi Medical Center (UMMC) at the rank of Professor and served as Vice Chair for Research in the Department of Psychiatry and Human Behavior. In 2010, he was awarded the Billy S Guyton Distinguished Professorship, the highest honor that is bestowed upon researchers at UMMC. While at UMMC, Bill's long-standing interest in how environmental circumstances shape the choice to take drugs gave rise to some of his most innovative work, including a foray into behavioral economics. He investigated the effects of delay of reinforcement on the choice to self-administer cocaine when non-drug alternatives were available. In 2007, Bill and his colleagues demonstrated hyperbolic discounting of delayed drug injections. He followed this study with others examining delay discounting of non-drug reinforcers in monkeys and found that monkeys discounted delayed drug injections less steeply than non-drug reinforcers providing further insight into how drugs can come to control behavior. Bill Woolverton was much admired by his colleagues and students. He had a very inquisitive mind and liked to challenge accepted scientific beliefs. He had a gentle way of guiding the development of his trainees and in engaging his research peers in the field. He loved to play and sing in the ever-shifting band of friends and colleagues that he cultivated primarily during his Mississippi years. He will be greatly missed. He is survived by his loving wife Candy Woolverton, and his son Chris and daughter Lucy.

Differences in social interaction- vs. cocaine reward in mouse vs. rat.

We previously developed rat experimental models based on the conditioned place preference (CPP) paradigm in which only four 15-min episodes of dyadic social interaction with a sex- and weight-matched male Sprague Dawley (SD) rat (1) reversed CPP from cocaine to social interaction despite continuing cocaine training, and (2) prevented the reacquisition/re-expression of cocaine CPP. In a concurrent conditioning schedule, pairing one compartment with social interaction and the other compartment with 15 mg/kg cocaine injections, rats spent the same amount of time in both compartments and the most rewarding sensory component of the composite stimulus social interaction was touch (taction). In the present study, we validated our experimental paradigm in C57BL/6 mice to investigate if our experimental paradigm may be useful for the considerable number of genetically modified mouse models. Only 71% of the tested mice developed place preference for social interaction, whereas 85% of the rats did. Accordingly, 29% of the mice developed conditioned place aversion (CPA) to social interaction, whereas this was true for only 15% of the rats. In support of the lesser likelihood of mice to develop a preference for social interaction, the average amount of time spent in direct contact was 17% for mice vs. 79% for rats. In animals that were concurrently conditioned for social interaction vs. cocaine, the relative reward strength for cocaine was 300-fold higher in mice than in rats. Considering that human addicts regularly prefer drugs of abuse to drug-free social interaction, the present findings suggest that our experimental paradigm of concurrent CPP for cocaine vs. social interaction is of even greater translational power if performed in C57BL/6 mice, the genetic background for most transgenic rodent models, than in rats.

A new view of the effect of dopamine receptor antagonism on operant performance for rewarding brain stimulation in the rat.

Previous studies of neuroleptic challenges to intracranial self-stimulation (ICSS) employed two-dimensional (2D) measurements (curve shifts). Results so obtained are ambiguous with regard to the stage of neural processing at which the drug produces its performance-altering effect. We substituted a three-dimensional (3D) method that measures reward-seeking as a function of both the strength and cost of reward. This method reveals whether changes in reward seeking are due to drug action prior to the output of the circuitry that performs spatiotemporal integration of the stimulation-induced neural activity. The aim of this study was to obtain new information about the stage of neural processing at which pimozide acts to alter pursuit of brain stimulation reward (BSR). Following treatment with pimozide (0.1mg/kg) or its vehicle, the proportion of trial time allocated to working for BSR was measured as a function of pulse frequency and opportunity cost. A surface defined by Shizgal's reward-mountain model was fitted to the drug and vehicle data. Pimozide lowered the cost required to decrease performance for a maximal BSR to half its maximal level but did not alter the pulse-frequency required to produce a reward of half-maximal intensity. Like indirect dopamine agonists, pimozide does not alter the sensitivity of brain reward circuity but changes reward-system gain, subjective effort costs, and/or the value of activities that compete with ICSS. The 3D method is more sensitive and informative than the 2D methods employed previously.

Validation and extension of the reward-mountain model

The reward-mountain model relates the vigor of reward seeking to the strength and cost of reward. Application of this model provides information about the stage of processing at which manipulations such as drug administration, lesions, deprivation states, and optogenetic interventions act to alter reward seeking. The model has been updated by incorporation of new information about frequency following in the directly stimulated neurons responsible for brain stimulation reward and about the function that maps objective opportunity costs into subjective ones. The behavioral methods for applying the model have been updated and improved as well. To assess the impact of these changes, two related predictions of the model that were supported by earlier work have been retested: (1) altering the duration of rewarding brain stimulation should change the pulse frequency required to produce a reward of half-maximal intensity, and (2) this manipulation should not change the opportunity cost at which half-maximal performance is directed at earning a maximally intense reward. Prediction 1 was supported in all six subjects, but prediction 2 was supported in only three. The latter finding is interpreted to reflect recruitment, at some stimulation sites, of a heterogeneous reward substrate comprising dual, parallel circuits that integrate the stimulation-induced neural signals.

Progressive-ratio Responding for Palatable High-fat and High-sugar Food in Mice

Foods that are rich in fat and sugar significantly contribute to over-eating and escalating rates of obesity. The consumption of palatable foods can produce a rewarding effect that strengthens action-outcome associations and reinforces future behavior directed at obtaining these foods. Increasing evidence that the rewarding effects of energy-dense foods play a profound role in overeating and the development of obesity has heightened interest in studying the genes, molecules and neural circuitry that modulate food reward. The rewarding impact of different stimuli can be studied by measuring the willingness to work to obtain them, such as in operant conditioning tasks. Operant models of food reward measure acquired and voluntary behavioral responses that are directed at obtaining food. A commonly used measure of reward strength is an operant procedure known as the progressive ratio (PR) schedule of reinforcement. In the PR task, the subject is required to make an increasing number of operant responses for each successive reward. The pioneering study of Hodos (1961) demonstrated that the number of responses made to obtain the last reward, termed the breakpoint, serves as an index of reward strength. While operant procedures that measure changes in response rate alone cannot separate changes in reward strength from alterations in performance capacity, the breakpoint derived from the PR schedule is a well-validated measure of the rewarding effects of food. The PR task has been used extensively to assess the rewarding impact of drugs of abuse and food in rats (e.g., 6-8), but to a lesser extent in mice. The increased use of genetically engineered mice and diet-induced obese mouse models has heightened demands for behavioral measures of food reward in mice. In the present article we detail the materials and procedures used to train mice to respond (lever-press) for a high-fat and high-sugar food pellets on a PR schedule of reinforcement. We show that breakpoint response thresholds increase following acute food deprivation and decrease with peripheral administration of the anorectic hormone leptin and thereby validate the use of this food-operant paradigm in mice.

Progressive-ratio Responding for Palatable High-fat and High-sugar Food in Mice

Foods that are rich in fat and sugar significantly contribute to over-eating and escalating rates of obesity. The consumption of palatable foods can produce a rewarding effect that strengthens action-outcome associations and reinforces future behavior directed at obtaining these foods. Increasing evidence that the rewarding effects of energy-dense foods play a profound role in overeating and the development of obesity has heightened interest in studying the genes, molecules and neural circuitry that modulate food reward1,2. The rewarding impact of different stimuli can be studied by measuring the willingness to work to obtain them, such as in operant conditioning tasks3. Operant models of food reward measure acquired and voluntary behavioral responses that are directed at obtaining food. A commonly used measure of reward strength is an operant procedure known as the progressive ratio (PR) schedule of reinforcement.4,5 In the PR task, the subject is required to make an increasing number of operant responses for each successive reward. The pioneering study of Hodos (1961) demonstrated that the number of responses made to obtain the last reward, termed the breakpoint, serves as an index of reward strength4. While operant procedures that measure changes in response rate alone cannot separate changes in reward strength from alterations in performance capacity, the breakpoint derived from the PR schedule is a well-validated measure of the rewarding effects of food. The PR task has been used extensively to assess the rewarding impact of drugs of abuse and food in rats (e.g.,6-8), but to a lesser extent in mice9. The increased use of genetically engineered mice and diet-induced obese mouse models has heightened demands for behavioral measures of food reward in mice. In the present article we detail the materials and procedures used to train mice to respond (lever-press) for a high-fat and high-sugar food pellets on a PR schedule of reinforcement. We show that breakpoint response thresholds increase following acute food deprivation and decrease with peripheral administration of the anorectic hormone leptin and thereby validate the use of this food-operant paradigm in mice.

Pontine and thalamic influences on fluid rewards: I. Operant responding for sucrose and corn oil

The reward strength of orosensory sucrose and corn oil was measured using fixed and progressive ratio operant schedules. Because the orosensory effects of the stimuli were of interest, Experiment 1 compared operant responses for sucrose in sham and real feeding rats. The results demonstrated that rats would work for sucrose solutions without the accompanying postingestive effects. Furthermore, the break points for high concentrations of sucrose (1.0M or 2.0M) were significantly higher in sham feeding rats than in real feeding controls. Experiment 2 investigated the role of the parabrachial nucleus (PBN) and of the thalamic orosensory area (TOA) in sucrose and corn oil reward. During free access, rats with PBN lesions (PBNx) licked significantly less sucrose solution than their controls, but both groups ingested a similar volume of corn oil emulsion. When an operant was imposed, these same PBNx rats failed to respond for sucrose and continued only modestly for corn oil. In contrast, the TOA lesioned rats (TOAx) showed no impairment in responding for sucrose or corn oil during either the free access or operant sessions. Furthermore, rats with TOA lesions demonstrated significantly higher break points for sucrose than did their controls. Together, the data imply that the PBN but not the TOA is critical for the perception of, or responding to the reward value of sucrose and corn oil.

Rattus Psychologicus: Construction of preferences by self-stimulating rats

Behavioral economists have proposed that human preferences are constructed during their elicitation and are thus influenced by the elicitation procedure. For example, different preferences are expressed when options are encountered one at a time or concurrently. This phenomenon has been attributed to differences in the “evaluability” of a particular attribute when comparison to an option with a different value of this attribute is or is not available. Research on the preferences of laboratory animals has often been carried out by means of operant-conditioning methods. Formal treatments of operant behavior relate preferences to variables such as the strength and cost of reward but do not address the evaluability of these variables. Two experiments assessed the impact of procedural factors likely to alter the evaluability of an opportunity cost (“price”): the work time required for a rat to earn a train of rewarding electrical brain stimulation. The results support the notion that comparison between recently encountered prices is necessary to render the price variable highly evaluable. When price is held constant over many trials and test sessions, the evaluability of this variable appears to decline. Implications are discussed for the design of procedures for estimating subjective reward strengths and costs in operant-conditioning experiments aimed at characterizing, identifying and understanding neural circuitry underlying evaluation and choice.

Appetitive olfactory learning in Drosophila larvae: effects of repetition, reward strength, age, gender, assay type and memory span

Associative plasticity is a basic characteristic of behaviour. We analysed associative olfactory learning in larval Drosophila, using a reciprocal conditioning assay. One group of animals was rewarded with fructose in the presence of odour A but not in the presence of odour B (A+/B); the companion group received reciprocal training (A/B+). During the test, larvae were given a choice between A and B; those that had received A+/B training showed a higher preference for A than reciprocally trained larvae did. As all other parameters were equal between groups, this difference was exclusively due to associative learning. Learning reached an asymptote after as few as three training trials and 2.0 mol/litre of fructose yielded asymptotic learning. Learning was not modulated by larval age tested 4, 5 and 6 days after egg laying or by gender. En masse assays confirmed the lack of gender differences. Memory was fully stable for at least 30 min. These experiments provide a basis for future investigations into the cellular and molecular underpinnings of appetitive olfactory learning in larval Drosophila.

A new learning algorithm for the hierarchical structure learning automata operating in the nonstationary S-model random environment

An extended algorithm of the relative reward strength algorithm is proposed. It is shown that the proposed algorithm ensures the convergence with probability I to the optimal path under the certain type of nonstationary environment. Several computer simulation results confirm the effectiveness of the proposed algorithm.