Effects of deprivation level on humans' self-control for food reinforcers

Gambling on an empty stomach: Hunger modulates preferences for learned but not described risks

INTRODUCTION

We assess risks differently when they are explicitly described, compared to when we learn directly from experience, suggesting dissociable decision-making systems. Our needs, such as hunger, could globally affect our risk preferences, but do they affect described and learned risks equally? On one hand, decision-making from descriptions is often considered flexible and context sensitive, and might therefore be modulated by metabolic needs. On the other hand, preferences learned through reinforcement might be more strongly coupled to biological drives.

METHOD

Thirty-two healthy participants (females: 20, mean age: 25.6 ± 6.5 years) with a normal weight (Body Mass Index: 22.9 ± 3.2 kg/m2 ) were tested in a within-subjects counterbalanced, randomized crossover design for the effects of hunger on two separate risk-taking tasks. We asked participants to choose between two options with different risks to obtain monetary outcomes. In one task, the outcome probabilities were described numerically, whereas in a second task, they were learned.

RESULT

In agreement with previous studies, we found that rewarding contexts induced risk-aversion when risks were explicitly described (F1,31  = 55.01, p < .0001, ηp 2  = .64), but risk-seeking when they were learned through experience (F1,31  = 10.28, p < .003, ηp 2  = .25). Crucially, hunger attenuated these contextual biases, but only for learned risks (F1,31  = 8.38, p < .007, ηp 2  = .21).

CONCLUSION

The results suggest that our metabolic state determines risk-taking biases when we lack explicit descriptions.

Deprivation Has Inconsistent Effects on Delay Discounting: A Review

Delay discounting, the tendency for outcomes to be devalued as they are more temporally remote, has implications as a target for behavioral interventions. Because of these implications, it is important to understand how different states individuals may face, such as deprivation, influence the degree of delay discounting. Both dual systems models and state-trait views of delay discounting assume that deprivation may result in steeper delay discounting. Despite early inconsistencies and mixed results, researchers have sometimes asserted that deprivation increases delay discounting, with few qualifications. The aim of this review was to determine what empirical effect, if any, deprivation has on delay discounting. We considered many kinds of deprivation, such as deprivation from sleep, drugs, and food in humans and non-human animals. For 23 studies, we analyzed the effect of deprivation on delay discounting by computing effect sizes for the difference between delay discounting in a control, or baseline, condition and delay discounting in a deprived state. We discuss these 23 studies and other relevant studies found in our search in a narrative review. Overall, we found mixed effects of deprivation on delay discounting. The effect may depend on what type of deprivation participants faced. Effect sizes for deprivation types ranged from small for sleep deprivation (Hedge's gs between −0.21 and 0.07) to large for opiate deprivation (Hedge's gs between 0.42 and 1.72). We discuss possible reasons why the effect of deprivation on delay discounting may depend on deprivation type, including the use of imagined manipulations and deprivation intensity. The inconsistency in results across studies, even when comparing within the same type of deprivation, indicates that more experiments are needed to reach a consensus on the effects of deprivation on delay discounting. A basic understanding of how states affect delay discounting may inform translational efforts.

Age-related effects in delay discounting for food

Developmental influences of growth, such as hormones and metabolic factors, increase food intake and weight across the lifespan. Delay discounting (DD), a choice procedure that characterizes preferences for immediate rewards, such as food, over larger, more delayed ones may be useful in understanding developmental and metabolic changes in decision making processes related to food intake. The present study examined the relation between age and food DD in a cross-sectional design. Other variables, such as pubertal stage, were examined also as these may influence discounting. Participants (N = 114; 28 children and 86 adult) from a community sample completed measures of food and money delay discounting to determine if age-related variation in discounting tendencies is food-specific or more general. Both measures yield an omnibus discounting value and three additional values for small, medium, and large magnitudes. Analyses first revealed magnitude effects-- smaller magnitudes of both food and money were discounted more steeply than larger magnitudes. Hierarchical regressions indicated subjective hunger predicted steeper food discounting. When subjective hunger was controlled, age, but not puberty, significantly predicted food discounting for omnibus, medium, and large magnitudes of food. In children, food discounting decreased from early childhood to late adolescence. In adults, food discounting increased from early to late adulthood. Neither age, puberty, nor obesity status predicted any measure of monetary discounting. Food discounting, then, appears to change across the lifespan, and therefore, may be appropriate to examine psychological processes that accompany developmental and metabolic changes across the lifespan.

Hunger improves reinforcement-driven but not planned action

Human decisions can be reflexive or planned, being governed respectively by model-free and model-based learning systems. These two systems might differ in their responsiveness to our needs. Hunger drives us to specifically seek food rewards, but here we ask whether it might have more general effects on these two decision systems. On one hand, the model-based system is often considered flexible and context-sensitive, and might therefore be modulated by metabolic needs. On the other hand, the model-free system's primitive reinforcement mechanisms may have closer ties to biological drives. Here, we tested participants on a well-established two-stage sequential decision-making task that dissociates the contribution of model-based and model-free control. Hunger enhanced overall performance by increasing model-free control, without affecting model-based control. These results demonstrate a generalized effect of hunger on decision-making that enhances reliance on primitive reinforcement learning, which in some situations translates into adaptive benefits.

THE RELATIVE REINFORCING VALUE OF SNACK FOOD IS A SIGNIFICANT PREDICTOR OF FAT LOSS IN WOMEN WITH OVERWEIGHT OR OBESITY

Reinforcing Relative Value (RRV) of food and impulsivity are associated with energy intake and obesity. The study investigated the degree to which changes in RRV and impulsivity independently or interactively predict change in body weight and composition in women with overweight or obesity engaged in either a fast or in a slow weight loss programs. Body weight, body composition, Impulsivity (Barratt Impulsiveness Scale), RRV snack (computerized Behavioural Choice Task) were measured at baseline and post-intervention in 30 women with obesity undergoing either slow (n= 14 -500 kcal/day, 20 weeks) or fast n=16 (-1000kcal/day, 10 weeks) weight reduction. No group*time effects were noted on body composition, impulsivity or RRV, so participants from both groups were pooled for analysis. Multiple regression analyses indicated that none of the impulsivity variables predicted weight- or fat mass (FM) loss. However, Δ RRV snack predicted ΔFM (r=0.40, P=0.046), whereby greater increases in RRV snack were associated with less FM loss. Results indicate that different rates of weight loss do not differentially affect RRV snack or impulsivity traits. However, changes in RRV snack predicted FM loss, suggesting that dietary interventions that either mitigate increases or foster reductions in the RRV snack may yield greater reductions in adiposity. Trial Registration clinicaltrials.gov identifier: NCT04866875 NOVELTY POINTS • No differences in RRV of food were noted between fast and slow weight loss • Weight loss from combined fast and slow groups led to a moderate-sized reduction in the total impulsivity • Greater diet-induced increases in RRV snack was associated with less body fat-loss.

Calorie deprivation impairs the self-control of eating, but not of other behaviors

OBJECTIVE

Sustained weight loss is difficult to achieve, and weight regain is common due to biological and psychological changes caused by calorie deprivation. These changes are thought to undermine weight loss efforts by making self-control more difficult. However, there is a lack of evidence showing a causal relationship between calorie deprivation and behavioral self-control.

DESIGN

In this longitudinal field experiment, we tested whether a ten-day period of calorie deprivation leads to the impairment of behavioral self-control. Participants were randomly assigned to either restrict their calorie intake or to continue eating normally for the study period.

MAIN OUTCOME MEASURES

Participants were given a box of food and non-food 'treats' (i.e., chocolates and lottery tickets) that they were asked to resist until the end of the study. On the last day, researchers recorded the number of treats that remained for each participant.

RESULTS

Nonparametric permutation tests revealed that calorie-deprived participants ate significantly more chocolates than control participants did (p = 0.036), but that participants did not differ in the number of lottery tickets 'scratched' by condition (p = 0.332).

CONCLUSION

This pattern of findings suggests that calorie deprivation impairs food-related self-control, but that this self-control deficit may not generalize beyond food-related tasks.

Impulsivity and self-control in elementary school children and adult females: Using identical task and procedural parameters

Results of studies examining the relationship between impulsivity and age are limited because different tasks, procedural parameters, and different reinforcers have been used with different aged participants. Thus, the current study sought to rectify these differences in two experiments with children (42, ages 5-12) and adults (69 college-aged females) using the same task with identical procedural parameters. In the Self-Control Video Software Task (SCVST; Forzano and Schunk, 2008; Forzano et al., 2014) participants repeatedly choose between larger, more delayed and smaller, less delayed access to viewing video cartoons. No differences in impulsivity were found between adults and children. No age or gender differences were found among children. Differences in task and procedural parameters are identified as important in their implications for research on impulsivity.

Hypothalamic-Extended Amygdala Circuit Regulates Temporal Discounting

Choice behavior is characterized by temporal discounting, i.e., preference for immediate rewards given a choice between immediate and delayed rewards. Agouti-related peptide (AgRP)-expressing neurons located in the arcuate nucleus of the hypothalamus (ARC) regulate food intake and energy homeostasis, yet whether AgRP neurons influence choice behavior and temporal discounting is unknown. Here, we demonstrate that motivational state potently modulates temporal discounting. Hungry mice (both male and female) strongly preferred immediate food rewards, yet sated mice were largely indifferent to reward delay. More importantly, selective optogenetic activation of AgRP-expressing neurons or their axon terminals within the posterior bed nucleus of stria terminalis (BNST) produced temporal discounting in sated mice. Furthermore, activation of neuropeptide Y (NPY) type 1 receptors (Y1Rs) within the BNST is sufficient to produce temporal discounting. These results demonstrate a profound influence of hypothalamic signaling on temporal discounting for food rewards and reveal a novel circuit that determine choice behavior.SIGNIFICANCE STATEMENT Temporal discounting is a universal phenomenon found in many species, yet the underlying neurocircuit mechanisms are still poorly understood. Our results revealed a novel neural pathway from agouti-related peptide (AgRP) neurons in the hypothalamus to the bed nucleus of stria terminalis (BNST) that regulates temporal discounting in decision-making.

Hunger increases delay discounting of food and non-food rewards

How do our valuation systems change to homeostatically correct undesirable psychological or physiological states, such as those caused by hunger? There is evidence that hunger increases discounting for food rewards, biasing choices towards smaller but sooner food reward over larger but later reward. However, it is not understood how hunger modulates delay discounting for non-food items. We outline and quantitatively evaluate six possible models of how our valuation systems modulate discounting of various commodities in the face of the undesirable state of being hungry. With a repeated-measures design, an experimental hunger manipulation, and quantitative modeling, we find strong evidence that hunger causes large increases in delay discounting for food, with an approximately 25% spillover effect to non-food commodities. The results provide evidence that in the face of hunger, our valuation systems increase discounting for commodities, which cannot achieve a desired state change as well as for those commodities that can. Given that strong delay discounting can cause negative outcomes in many non-food (consumer, investment, medical, or inter-personal) domains, the present findings suggest caution may be necessary when making decisions involving non-food outcomes while hungry.

Hunger and socioeconomic background additively predict impulsivity in humans

Impulsivity refers to the valuation of future rewards relative to immediate ones. From an evolutionary perspective, we should expect impulsivity to be sensitive to the current state of the organism (for example, hunger), and also its long-term developmental history. There is evidence that both current hunger and childhood socioeconomic deprivation are individually associated with impulsivity, but it is not known how these combine. For example, acute hunger might over-ride social gradients in baseline impulsivity, or alternatively, individuals who have experienced greater deprivation might respond more strongly to acute hunger. We aimed to investigate whether hunger and childhood socioeconomic deprivation act additively or interactively in three studies utilising delay discounting tasks. Childhood socioeconomic deprivation was measured using childhood postcode and a self-report measure. In two studies hunger was experimentally manipulated (n = 95 & n = 93 respectively), and in the third we simply measured natural variation. We employed a standard hypothetical delay discounting task in two studies, and a behavioural task with experienced delays in the third (n = 330). Although the individual studies varied in which predictors were statistically significant, when we meta-analysed them, a clear pattern emerged. Hunger predicted greater impulsivity; childhood socioeconomic deprivation predicted greater impulsivity; and these two effects were additive rather than interactive.

Toward a Unifying Account of Impulsivity and the Development of Self-Control

Impulsivity has traditionally been thought to involve various behavioral traits that can be measured using different laboratory protocols. Whereas some authors regard different measures of impulsivity as reflecting fundamentally distinct and unrelated behavioral tendencies (fragmentation approach), others regard those different indexes as analogue forms of the same behavioral tendency, only superficially different (unification approach). Unifying accounts range from mere intuitions to more sophisticated theoretical systems. Some of the more complete attempts at unifying are intriguing but have validity weaknesses. We propose a new unifying attempt based on theoretical points posed by other authors and supplemented by theory and research on associative learning. We then apply these assumptions to characterize the paradigms used to study impulsivity in laboratory settings and evaluate their scope as an attempt at unification. We argue that our approach possesses a good balance of parsimony and empirical and theoretical grounding, as well as a more encompassing scope, and is more suitable for experimental testing than previous theoretical frameworks. In addition, the proposed approach is capable of generating a new definition of impulsivity and outlines a hypothesis of how self-control can be developed. Finally, we examine the fragmentation approach from a different perspective, emphasizing the importance of finding similarities among seemingly different phenomena.

Does Hunger Contribute to Socioeconomic Gradients in Behavior?

Recent research has uncovered many examples of socioeconomic gradients in behavior and psychological states. As yet there is no theoretical consensus on the nature of the causal processes that produce these gradients. Here, I present the hunger hypothesis, namely the claim that part of the reason that people of lower socioeconomic position behave and feel as they do is that they are relatively often hungry. The hunger hypothesis applies in particular to impulsivity-hyperactivity, irritability-aggression, anxiety, and persistent narcotic use, all of which have been found to show socioeconomic gradients. I review multiple lines of evidence showing that hunger produces strong increases in these outcomes. I also review the literatures on food insufficiency and food insecurity to show that, within affluent societies, the poor experience a substantial burden of hunger, despite obtaining sufficient or excess calories on average. This leads to the distinctive prediction that hunger is an important mediator of the relationships between socioeconomic variables and the behavioral/psychological outcomes. This approach has a number of far-reaching implications, not least that some behavioral and psychological differences between social groups, though persistent under current economic arrangements, are potentially highly reversible with changes to the distribution of financial resources and food.

Impulse control and restrained eating among young women: Evidence for compensatory cortical activation during a chocolate-specific delayed discounting task

Theory and associated research indicate that people with elevated restrained eating (RE) scores have higher risk for binge eating, future bulimic symptom onset and weight gain. Previous imaging studies have suggested hyper-responsive reward brain area activation in response to food cues contributes to this risk but little is known about associated neural impulse control mechanisms, especially when considering links between depleted cognitive resources related to unsuccessful RE. Towards illuminating this issue, we used a chocolate-specific delayed discounting (DD) task to investigate relations between RE scores, behavior impulsivity, and corresponding neural impulse control correlates in a functional magnetic resonance imaging (fMRI) study of 27 young women. Specifically, participants were required to choose between more immediate, smaller versus delayed, larger hypothetical chocolate rewards following initial consumption of a chocolate. As predicted, RE scores were correlated positively with behavior impulse control levels. More critically, higher RE scores were associated with stronger activation in impulse control region, the dorsal-lateral prefrontal cortex (DLPFC) during the completion of difficult decision trials reflecting higher cognitive demands and resource depletion relative to easy decision trials. Exploratory analyses revealed a positive correlation between RE scores and activity in a reward system hub, the right striatum. Moreover, a positive correlation between left DLPFC and striatum activation was posited to reflect, in part, impulse control region compensation in response to stronger reward signal among women with RE elevations. Findings suggested impulse control lapses may contribute to difficulties in maintaining RE, particularly when cognitive demands are high.

A Computational Analysis of Aberrant Delay Discounting in Psychiatric Disorders

Impatience for reward is a facet of many psychiatric disorders. We draw attention to a growing literature finding greater discounting of delayed reward, an important aspect of impatience, across a range of psychiatric disorders. We propose these findings are best understood by considering the goals and motivation for discounting future reward. We characterize these as arising from either the opportunity costs of waiting or the uncertainty associated with delayed reward. We link specific instances of higher discounting in psychiatric disorder to heightened subjective estimates of either of these factors. We propose these costs are learned and represented based either on a flexible cognitive model of the world, an accumulation of previous experience, or through evolutionary specification. Any of these can be considered suboptimal for the individual if the resulting behavior results in impairments in personal and social functioning and/or in distress. By considering the neurochemical and neuroanatomical implementation of these processes, we illustrate how this approach can in principle unite social, psychological and biological conceptions of impulsive choice.

Spontaneous regional brain activity links restrained eating to later weight gain among young women

Theory and prospective studies have linked restrained eating (RE) to risk for future weight gain and the onset of obesity, but little is known about resting state neural activity that may underlie this association. To address this gap, resting fMRI was used to test the extent to which spontaneous neural activity in regions associated with inhibitory control and food reward account for potential relations between baseline RE levels and changes in body weight among dieters over a one-year interval. Spontaneous regional activity patterns corresponding to RE were assessed among 50 young women using regional homogeneity (ReHo) analysis, which measured temporal synchronization of spontaneous fluctuations within a food deprivation condition. Analyses indicated higher baseline RE scores predicted more weight gain at a one-year follow-up. Furthermore, food-deprived dieting women with high dietary restraint scores exhibited more spontaneous local activity in brain regions associated with the expectation and valuation for food reward [i.e., orbitofrontal cortex (OFC)/ventromedial prefrontal cortex (VMPFC)] and reduced spontaneous local activity in inhibitory control regions [i.e., bilateral dorsal-lateral prefrontal cortex (DLPFC)] at baseline. Notably, the association between baseline RE and follow-up weight gain was mediated by decreased local synchronization of the right DLPFC in particular and, to a lesser degree, increased local synchronization of the right VMPFC. In conjunction with previous research, these findings highlight possible neural mechanisms underlying the relation between RE and risk for weight gain.

Effects of mindful eating training on delay and probability discounting for food and money in obese and healthy-weight individuals

Obese individuals tend to behave more impulsively than healthy weight individuals across a variety of measures, but it is unclear whether this pattern can be altered. The present study examined the effects of a mindful eating behavioral strategy on impulsive and risky choice patterns for hypothetical food and money. In Experiment 1, 304 participants completed computerized delay and probability discounting tasks for food-related and monetary outcomes. High percent body fat (PBF) predicted more impulsive choice for food, but not small-value money, replicating previous work. In Experiment 2, 102 randomly selected participants from Experiment 1 were assigned to participate in a 50-min workshop on mindful eating or to watch an educational video. They then completed the discounting tasks again. Participants who completed the mindful eating session showed more self-controlled and less risk-averse discounting patterns for food compared to baseline; those in the control condition discounted similarly to baseline rates. There were no changes in discounting for money for either group, suggesting stimulus specificity for food for the mindful eating condition.

Choices between segmented and unsegmented schedules and the self-control paradigm

A concurrent-chains procedure was used to examine choice between a segmented (two- or three-terminal-link segments schedules) and an unsegmented schedule (simple schedule) in terminal links with equal interreinforcement intervals. In most such experiments, preference for the unsegmented schedule has been found, but in a recent study with humans (Alessandri et al., 2010) a reversal in preference was found when, in the segmented schedule, the terminal link segmenting stimulus was presented briefly and closer to food delivery such that the early terminal link stimulus was temporally closer to the food delivery. In Experiment 1, an attempt to replicate this latter effect with pigeons was unsuccessful but this outcome was consistent with an account in terms of a self-control contingency involving conditioned reinforcers. According to this account, the unsegmented alternative consisted of an immediate, smaller presentation of a conditioned reinforcer (i.e., the impulsive, and thus usually the preferred, option in several experiments) and the segmented schedule led to a delayed, larger conditioned reinforcer (i.e., the self-control option). In Experiment 2, a reversal of preference toward the segmented schedule was found when a delay was added to both terminal links between the reinforced initial-link response and the onset of the corresponding terminal link stimulus. This result is consistent with a similar effect found with primary reinforcers in the self-control literature suggesting the utility of self-control as an account of preferences for unsegmented terminal links of concurrent chains schedules.

Mapping the tip of the tongue--deprivation, sensory sensitisation, and oral haptics

We investigated the impact of food deprivation on oral and manual haptic size perception of food and non-food objects. From relevant theories (need-proportional perception, motivated perception, frustrative nonreward, perceptual defence, and sensory sensitisation) at least four completely different competing predictions can be derived. Testing these predictions, we found across four experiments that participants estimated the length of both non-food and food objects to be larger when hungry than when satiated, which was true only for oral haptic perception, while manual haptic perception was not influenced by hunger state. Subjectively reported hunger correlated positively with estimated object size in oral, but not in manual, haptic perception. The impact of food deprivation on oral perception vanished after oral stimulations even for hungry individuals. These results favour a sensory sensitisation account maintaining that hunger itself does not alter oral perception but the accompanying lack of sensory stimulation of the oral mucosa. Both oral and manual haptic perception tended to underestimate actual object size. Finally, an enhancing effect of domain-target matching was found, ie food objects were perceived larger by oral than by manual haptics, while non-food objects were perceived larger by manual than by oral haptics.

Percent body fat is related to delay and probability discounting for food in humans

This study describes delay and probability discounting patterns for hypothetical food and money in relation to percent body fat (PBF). Sixty university students completed four computerized discounting tasks in which they were asked to make a series of hypothetical decisions between (a) 10 dollars after one of several different delays (1, 2, 30, 180, and 365 days) or a smaller amount of money available immediately; (b) 10 bites of food after one of several delays (1, 2, 5, 10, and 20h) or a smaller number of bites available immediately; (c) $10 at one of several probabilities (0.9, 0.75, 0.5, 0.25, 0.1) or a smaller amount of money to be received for sure; and (d) 10 bites of food at one of several probabilities (0.9, 0.75, 0.5, 0.25, 0.1) or a smaller number of bites to be received for sure. Median indifference points for all participants across each task were well described using the hyperbolic discounting function. Results suggest that percent body fat predicted discounting for hypothetical food, but not money, using regression analyses with the entire sample and when comparing individuals in the high and low quartiles for PBF. None of the other dietary variables (body mass index, subjective hunger, and time since last meal or snack) were related to discounting patterns. This suggests that individuals with high PBF may exhibit heightened sensitivities to delay and probability when making decisions about food.

Gender differences in delay-discounting under mild food restriction

Impulsivity, a core symptom of attention-deficit hyperactivity disorder (ADHD), is tested in animal models by delay-discounting tasks. So far, mainly male subjects have been used in this paradigm at severe levels of food restriction. Here we studied the impulsive behaviour of CD-1 adult male and female mice at mild levels of food restriction. Mice maintained at 90 +/- 5% of ad libitum bodyweight, were tested in operant chambers provided with nose-poking holes. Nose poking in one hole resulted in the immediate delivery of one food pellet (small-soon, SS), whereas nose poking in the other hole delivered five food pellets after a delay (large-late, LL), which was increased progressively each day (0-150 s). Two subgroups emerged: individuals that shifted at short delays ("steep") and individuals that did not shift, even at the highest delays ("flat"). Analysis showed that "steep" females shifted at shorter delays than "steep" males, while no difference existed between males and females within the "flat" sub-population. In home-cage circadian activity as well as in a novelty-seeking test, females were more active than males. It can be concluded from these results that female mice are more impulsive than male mice under mild food restriction. This is in contrast with findings in earlier studies with more severe food restriction. Therefore, an alternative explanation is that females are more explorative, and that different features might be tested in delay-discounting paradigms, depending on restriction levels.

Use of an operant task to estimate food reinforcement in adult humans with and without BED

OBJECTIVE

The purpose of this study was to demonstrate the utility of food-reinforced operant task performance in modeling binge-eating disorder (BED). We hypothesized that food reinforcement after a caloric preload would be related to BED status, but not hunger.

METHODS AND PROCEDURES

We investigated the association between reports of hunger, binge tendency, and food reinforcement in a sample of 18 women (12 non-BED, 7 lean, 5 obese, and 6 obese BED). Participants completed two sessions of operant task performance after consuming 600 ml of flavored water or 600 ml of a 1 kcal/ml liquid meal.

RESULTS

Under the water condition, food reinforcement did not differ between the non-BED and BED groups, and was positively correlated with hunger ratings across all participants (r = 0.55, P = 0.023). Under the liquid meal condition, food reinforcement was significantly decreased compared with the water condition in the non-BED group (t = -2.6, P = 0.026). There was also a significant difference between the non-BED and BED groups in the fed condition (41 +/- 40, 117 +/- 60, F = 10.3, P = 0.005, non-BED vs. BED, respectively, mean +/- s.d.). The correlation between food reinforcement and hunger remained significant only in the non-BED group (r = 0.69, P = 0.011).

DISCUSSION

Our results support the hypothesis that food reinforcement measured after a caloric preload is related to BED status but not hunger in those subjects with BED. The data also suggest that operant task performance can be useful in modeling BED criteria such as "eating when not physically hungry."

Rats show preference for delayed rewards on the radial maze

Rats on an eight-arm radial maze chose between four arms on which a small reward could be obtained after a short delay and four arms on which a larger reward could be obtained after a longer delay. Experiments 1 and 2 showed that rats preferred the long-delay, large-reward arms over the short-delay, small-reward arms. This preference was particularly marked when the arms were made into enclosed alleys. Experiment 3 showed that this effect was not produced by a preference for staying in enclosed alleys. We argue that the rats endured longer delays to obtain larger rewards when fear of predation was minimized.

A review of delay-discounting research with humans: relations to drug use and gambling

Delay discounting represents the extent to which consequences, or outcomes, decrease in effectiveness to control behavior as a function of there being a delay to their occurrence. Higher rates of delay discounting are often operationalized as an index of impulsivity, and as such impulsive discounting may hold considerable potential for understanding fundamental behavioral processes associated with a range of problematic behaviors - including drug use and pathological gambling. This paper first provides a review of several assessment methods used in delay-discounting research with humans. Following, the delay-discounting literature related to drug use and gambling is reviewed. Consistencies across this literature are identified; and future research directions are discussed, which include (a) improving methods of assessment for delay discounting and (b) moving drug-use research progressively to causal interpretations, with high rates of delay discounting either predisposing to drug use or resulting from drug use itself.

Delay aversion but preference for large and rare rewards in two choice tasks: implications for the measurement of self-control parameters

Background

Impulsivity is defined as intolerance/aversion to waiting for reward. In intolerance-to-delay (ID) protocols, animals must choose between small/soon (SS) versus large/late (LL) rewards. In the probabilistic discount (PD) protocols, animals are faced with choice between small/sure (SS) versus large/luck-linked (LLL) rewards. It has been suggested that PD protocols also measure impulsivity, however, a clear dissociation has been reported between delay and probability discounting.

Results

Wistar adolescent rats (30- to 46-day-old) were tested using either protocol in drug-free state. In the ID protocol, animals showed a marked shift from LL to SS reward when delay increased, and this despite adverse consequences on the total amount of food obtained. In the PD protocol, animals developed a stable preference for LLL reward, and maintained it even when SS and LLL options were predicted and demonstrated to become indifferent. We demonstrate a clear dissociation between these two protocols. In the ID task, the aversion to delay was anti-economical and reflected impulsivity. In the PD task, preference for large reward was maintained despite its uncertain delivery, suggesting a strong attraction for unitary rewards of great magnitude.

Conclusion

Uncertain delivery generated no aversion, when compared to delays producing an equivalent level of large-reward rarefaction. The PD task is suggested not to reflect impulsive behavior, and to generate patterns of choice that rather resemble the features of gambling. In summary, present data do indicate the need to interpret choice behavior in ID and PD protocols differently.

Measuring impulsivity and modeling its association with cigarette smoking

Two types of behavioral measure are primarily used to examine impulsivity in humans and animals: Go/No-go tasks to assess inhibition and relative preference tasks to assess delay aversion. Several examples of each type of task are described so that common cognitive processes and variables affecting performance can be identified. Data suggest that smokers are more impulsive on each of these impulsivity measures than nonsmokers. Several models can be proposed to account for this group difference: (a) the differences predate and, possibly, are causally related to the initiation of cigarette smoking; (b) higher levels of impulsivity are associated with continued smoking, either through an association with heightened positive subjective effects of nicotine or heightened negative effects of nicotine abstinence (withdrawal); (c) nicotine causes neuroadaptations that result in elevated impulsivity in smokers. Studies relating to each of these models are reviewed, and it is concluded that all three models may contribute to the observed higher levels of impulsivity in smokers. However, pertinent studies are limited and additional systematic research is needed.

Measurement of delay discounting using trial-by-trial consequences

DELAY DISCOUNTING IN HUMANS WAS INVESTIGATED USING THREE DIFFERENT PROCEDURES: a frequently used discounting procedure with hypothetical rewards and delays; a procedure with hypothetical rewards and delays compressed down to much smaller values; and a contingent procedure in which each choice had a direct consequence. In the contingent procedure, on every trial, participants actually experienced the delay and obtained the reward amount associated with their choice. Each participant was exposed to all three procedures. Orderly temporal discounting patterns were obtained in all three procedures and described well by a hyperbolic model. Comparisons of the data revealed patterns unique to each procedure. The distributions of the discounting measures differed across the three procedures. In the contingent procedure, several subjects showed no discounting, e.g. complete self-control. Procedural factors in studies of impulsivity are discussed, and suggestions are offered for experiments in which the contingent-discounting procedure may prove useful.

The relative-reinforcing value of food under differing levels of food deprivation and restriction

Food deprivation and restriction both increase food consumption. Food deprivation also increases the reinforcing value of food, but it is unknown if food restriction alone or combined with deprivation increases the reinforcing value of food. Forty, normal-weight, college-aged, unrestrained females were randomized to one of four conditions that crossed food deprivation (Dep) and restriction (Res): Dep/Res, Dep/No Res, No Dep/Res, No Dep/No Res. All participants arrived at least 13h food-deprived, and non-deprived participants consumed at least 365cal from a drink during the session. Restriction was manipulated by placing snack food in front of participants, without access for 15min during the session, or having no snack food placed in front of participants. Following the experimental manipulations, participants completed a computer choice task to determine the reinforcing value of food. Repeated measures analysis of variance found a significant main effect of deprivation (p<0.05) and trials (p<0.001) for food points earned. Deprived participants found food to be more reinforcing, and the reinforcing value of food decreased over time. This suggests that while short-term food deprivation increases the relative-reinforcing value of food, short-term food restriction has no effect on the relative-reinforcing value of food in unrestrained eaters.

Increased impulsivity in cocaine dependent subjects independent of antisocial personality disorder and aggression

Several previous studies show a relationship between impulsivity and substance abuse; however, it is unclear whether the increased impulsivity seen in substance dependent groups is specifically related to substance abuse, or if it is due to concomitant antisocial personality disorder (ASPD) or aggression. The issue of whether impulsivity is specifically related to substance abuse is important since it has a bearing on risk factors for development of substance abuse. To determine whether cocaine dependent subjects show increased impulsivity independent of ASPD, the Barratt impulsiveness scale (BIS-11), a delayed reward laboratory measure of impulsivity, and the life history of aggression scale were administered to 49 cocaine dependent subjects and 25 controls. Results showed that cocaine dependent subjects with ASPD were more impulsive and aggressive than controls, but cocaine dependent subjects without ASPD were also more impulsive compared to controls. Controlling for aggression history, cocaine dependent subjects without ASPD continued to have elevated impulsivity as measured by the BIS-11, but not the delayed reward task. This study supports the hypothesis that the increased impulsivity as measured by the BIS-11 in cocaine dependent individuals is not exclusively due to concomitant increases in aggression or ASPD.

Pseudoparadoxical impulsivity in restrictive anorexia nervosa: a consequence of the logic of scarcity

OBJECTIVE

To explain an apparently paradoxical pattern wherein sufferers of restrictive anorexia nervosa exhibit both rigorous self-restraint and episodic impulsivity.

METHOD

The experimental, historical, and clinical literatures were examined for evidence of psychological and behavioral changes accompanying severe dietary constriction; such changes were noted and compared with those reported to occur in anorexics.

RESULTS

Increased impulsivity in association with dietary constriction is described in diverse literatures. A number of lines of evidence suggest that the serotonergic system mediates this change.

DISCUSSION

Many forms of impulsivity can be understood as having once constituted fitness-enhancing responses to resource scarcity. It is suggested that an evolved psychological mechanism calibrates the individual's sensitivity to risk in light of future prospects. Self-injurious behaviors are explicable as misfirings of such a mechanism. Similarly, excessive exercising by anorexics may reflect the misdirection of reward systems that normally encourage adaptive increases in ranging behavior under conditions of scarcity.

Self-control: theory and research

Theory and research on self-control were reviewed. Selected research is summarized along with some conclusions from clinical practice. Self-control difficulties are of central importance for many psychiatric disorders. Self-control is also a crucial, and often missing, ingredient for success in most treatment programs. It is stable enough to be considered an enduring trait or skill, but not immutable. Performance tests provide ingenious methods of measuring it, and they have some advantages over questionnaires. Biological research is under way: the prefrontal cortex is heavily involved; alcohol reduces self-control; serotonin may increase it. Self-control is correlated with, but not identical with, capacity for focused attention. Self-control is subject to "momentum effects": the more it is successfully practiced in a given arena, the easier subsequent practice usually becomes, and vice versa. Like a muscle, it appears to be fatigued in the short run and strengthened in the long run by exercise.

Does previous protein feeding affect the response of sheep towards foods that differ in their rumen availability, but not content, of nitrogen?

The objective of the experiment was threefold: (1) to test whether an 'unlearned appetite' for dietary protein exists in sheep, (2) whether such an appetite and subsequent diet selection depend on the degree of previous protein deprivation, and (3) whether the N-source in the foods offered as choice influences diet selection. Differences in protein deprivation were achieved by feeding sheep with food either with high (HP) or low (LP) protein. Sheep were fed on Food LP, either for the same period of time as sheep on Food HP or until they reached the same live-weight (LW) as sheep on Food HP. Following the feeding regimes that induced differences in animal state, sheep were given a choice between a novel low-protein food (T) or Food T supplemented with isonitrogenous amounts with one of three nitrogen sources: urea (U), casein (C), or formaldehyde-treated casein (TFC). Diet selection measured in the short-term or over the first few days did not provide any evidence in support of an unlearned appetite for protein by sheep of different states. In fact, diet selection by all animals was characterized by an avoidance of the foods supplemented with the three nitrogen sources. This avoidance was strongest for the food supplemented with formaldehyde-treated casein. Selection of considerable amounts of supplemented foods was gradual and consistent only after animals gained experience of them, i.e. were allowed to consume a single supplemented food for a period of 7 days. Following this period, animals that had previously consumed Food LP for the same period of time as animals on Food HP selected a higher proportion of the supplemented food than the other sheep. The results support the view that there is no unlearned appetite for protein in sheep, and that control over diet selection is learned.

Limited access to a dietary fat option affects ingestive behavior but not body composition in male rats

Restricting access to high-fat foods is a common strategy utilized to promote health. This strategy may contribute to episodes of overconsumption, however, when the restricted foods subsequently become available. The present study utilized a rat feeding procedure to determine if restricting access to an optional source of dietary fat would increase later consumption of that food under nonenergy-deprived conditions. Five groups of male Sprague-Dawley rats were used, all of which had continuous access to a standard rodent diet and water. The control group had no access to shortening. The low-restriction group had 2-h access to shortening every day. The high-restriction group had 2-h access to shortening on Monday, Wednesday, and Friday. Two additional groups were switched between the high and low conditions. Two-hour and 24-h food intakes were measured every day for 6 weeks. At the end of the study rats were sacrificed and carcass composition determined. As access to the shortening decreased, consumption during the 2-h access period increased. Rats compensated for the increased shortening consumption by decreasing intake of the standard diet. Thus, cumulative energy consumption did not differ among the groups. When switched between the high and low conditions, rats rapidly adjusted to the change in shortening availability. There were no effects of access schedule on carcass composition. These results indicate that restricting access to an optional high-fat food, even under nonenergy-deprived conditions, can promote significant increases in the consumption of that food when it subsequently becomes available.

Laboratory Research on Self-Control: Applications to Administration

Administrators must sometimes choose between a less delayed but ultimately less valued outcome (impulsiveness) and a more delayed but ultimately more valued outcome (self-control). Which choice is made can affect the long-term health of an administrator's organization. Self-control laboratory research and analysis can be useful in understanding and possibly modifying these choices. This article describes some of the extensive basic laboratory research and analysis concerning self-control and applies this information to specific situations in administration, particularly higher education administration. It discusses the various factors that affect self-control and examines choices between negative, as well as positive, outcomes. Laboratory and nonlaboratory investigations can benefit from attending to information obtained from the other domain.