Food Reward Research Articles

Food image validation for assessing diurnal patterns of appetite and food reward in individuals ranging in BMI with and without type 2 diabetes

Increasing scientific interest in diurnal patterns of appetite and food reward means it is important to employ valid methodologies that are time-of-day appropriate. Moreover, it is unknown whether people with type 2 diabetes (T2D) experience similar diurnal patterns to healthy individuals. The Steno Biometric Food Preference Task (SBFPT)(1) utilises an array of food images to assess food reward and biometric responses to food cues varying in fat content and sweet taste. We aimed to adapt and validate the SBFPT to assess diurnal appetite and food reward in Danish adults with a range of BMI with/without T2D.An anonymous online survey was used to validate 28 food images (7 high-fat sweet (HFSW), 7 lowfat sweet (LFSW), 7 high-fat savoury (HFSA) and 7 low-fat savoury (LFSA)) in Danish residents in order to select 16 images for the diurnal-SBFPT (4 from each category). For each food image, participants had to name the food, report the frequency of consumption, and rate its tastiness, sweetness, fat content, appropriateness to consume in the morning (between 8:00-12:00), afternoon (between 12:00-16:00), and evening (between 16:00-20:00) on a 100-mm visual analogue scale(2).We obtained 207 complete responses (with >80% completion). Participants included 61 men, 144 women and 2 not specified. Of these, 124 did not have T2D and 83 had T2D with a median [Q1, Q3] diagnosis duration of 12 [8, 18] years. Median [Q1, Q3] age was 61 [50, 67] years and BMI was 26.4 [23.4, 31.8] kg/m2. After data were cleaned, the mean of the individual ratings for each food was calculated and adequacy was judged according to pre-specified criteria(2). As there were overall differences in ratings of appropriate consumption time between those with/without T2D regardless of time of day (linear mixed model β = -5.3mm; p=.01), a difference score between morning (AM) and afternoon/evening (PM) ratings was computed (AM-PM difference). Adequacy for this criterion was based on foods with the smallest absolute mean across those with/without T2D and smallest absolute difference between groups.Overall, the majority of the final 4 images from each food category met the criteria for recognition, frequency of consumption, liking, taste and perceived fat content. LFSW foods had the smallest absolute AM-PM differences (i.e., more similar appropriateness scores in AM vs PM; range 110mm), followed by LFSA (5-21mm), HFSA (8-21mm) and HFSW (8-38mm).This image validation study will allow us to examine appetite and food reward across the day using a validated tool among Danish adults ranging in BMI with/without T2D. Future studies should consider the perceived appropriateness of the foods selected for appetite-related assessments in T2D, especially high-fat sweet foods.

Sleep, Health Outcomes and Body Weight (SHOW) study: a measurement burst design study on sleep and risk factors for obesity in black emerging adults in North Carolina, USA

IntroductionBlack emerging adults (18–28 years) have the highest risk of short sleep duration and obesity. This increased risk may be partly explained by greater stress levels, which may result from...

Lack of Bmal1 leads to changes in rhythmicity and impairs motivation towards natural stimuli.

Maintaining proper circadian rhythms is essential for coordinating biological functions in mammals. This study investigates the effects of daily arrhythmicity using Bmal1-knockout (KO) mice as a model, aiming to understand behavioural and motivational implications. By employing a new mathematical analysis based on entropy divergence, we identified disrupted intricate activity patterns in mice derived by the complete absence of BMAL1 and quantified the difference regarding the activity oscillation's complexity. Changes in locomotor activity coincided with disturbances in circadian gene expression patterns. Additionally, we found a dysregulated gene expression profile particularly in brain nuclei like the ventral striatum, impacting genes related to reward and motivation. Further investigation revealed that arrhythmic mice exhibited heightened motivation for food and water rewards, indicating a link between circadian disruptions and the reward system. This research sheds light on how circadian clock alterations impact the gene expression regulating the reward system and how this, in turn, can lead to altered seeking behaviour and motivation for natural rewards. In summary, the present study contributes to our understanding of how reward processing is under the regulation of circadian clock machinery.

Value-Driven Adaptations of Mesolimbic Dopamine Release Are Governed by Both Model-Based and Model-Free Mechanisms.

The magnitude of dopamine signals elicited by rewarding events and their predictors is updated when reward value changes. It is actively debated how readily these dopamine signals adapt and whether adaptation aligns with model-free or model-based reinforcement-learning principles. To investigate this, we trained male rats in a pavlovian-conditioning paradigm and measured dopamine release in the nucleus accumbens core in response to food reward (unconditioned stimulus) and reward-predictive conditioned stimuli (CS), both before and after reward devaluation, induced via either sensory-specific or nonspecific satiety. We demonstrate that (1) such devaluation reduces CS-induced dopamine release rapidly, without additional pairing of CS with devalued reward and irrespective of whether the devaluation was sensory-specific or nonspecific. In contrast, (2) reward devaluation did not decrease food reward-induced dopamine release. Surprisingly, (3) postdevaluation reconditioning, by additional pairing of CS with devalued reward, rapidly reinstated CS-induced dopamine signals to predevaluation levels. Taken together, we identify distinct, divergent adaptations in dopamine-signal magnitude when reward value is decreased: CS dopamine diminishes but reinstates fast, whereas reward dopamine is resistant to change. This implies that, respective to abovementioned findings, (1) CS dopamine may be governed by a model-based mechanism and (2) reward dopamine by a model-free one, where (3) the latter may contribute to swift reinstatement of the former. However, changes in CS dopamine were not selective for sensory specificity of reward devaluation, which is inconsistent with model-based processes. Thus, mesolimbic dopamine signaling incorporates both model-free and model-based mechanisms and is not exclusively governed by either.

Involvement of dopamine D3 receptor in impulsive choice decision-making in male rats

Impulsive decision-making has been linked to impulse control disorders and substance use disorders. However, the neural mechanisms underlying impulsive choice are not fully understood. While previous PET imaging and autoradiography studies have shown involvement of dopamine and D2/3 receptors in impulsive behavior, the roles of distinct D1, D2, and D3 receptors in impulsive decision-making remain unclear. In this study, we used a food reward delay-discounting task (DDT) to identify low- and high-impulsive rats, in which low-impulsive rats exhibited preference for large delayed reward over small immediate rewards, while high-impulsive rats showed the opposite preference. We then examined D1, D2, and D3 receptor gene expression using RNAscope in situ hybridization assays. We found that high-impulsive male rats exhibited lower levels of D2 and D3, and particularly D3, receptor expression in the nucleus accumbens (NAc), with no significant changes in the insular, prelimbic, and infralimbic cortices. Based on these findings, we further explored the role of the D3 receptor in impulsive decision-making. Systemic administration of a selective D3 receptor agonist (FOB02-04) significantly reduced impulsive choices in high-impulsive rats but had no effects in low-impulsive rats. Conversely, a selective D3 receptor antagonist (VK4-116) produced increased both impulsive and omission choices in both groups of rats. These findings suggest that impulsive decision-making is associated with a reduction in D3 receptor expression in the NAc. Selective D3 receptor agonists, but not antagonists, may hold therapeutic potentials for mitigating impulsivity in high-impulsive subjects.

Domestic chickens solving mirror-mediated spatial location tasks uncovering their cognitive abilities

The increasing demand on adapting modern livestock farming to higher animal welfare standards requires a thorough understanding of a species’ cognitive abilities to determine their adaptability. With the chicken being the world’s most numerous birds in animal production, it is mandatory to identify its cognitive abilities and limitations in order to meet its needs. We investigated if chickens are able to use and understand the reflective properties of a mirror that is the correlation of reflections of food rewards and their real location. In total, 18 female chickens of two different breeds were tested in a mirror-mediated spatial location task. Eleven out of eighteen hens solved the task successfully and thus, possibly exploited the correlation between the reflection in the mirror and the real food reward. We found differences on a breed and on the individual level, with different amounts of time needed learning the association of reward and mirror image. The results imply sophisticated cognitive abilities in chickens, assuming they may be able to understand how mirror images represent objects in the real environment, and to make use of it during foraging. The chicken’s cognitive ability might lead to a new understanding and provision of animal welfare-compliant production environments.

Individual variability and consistency of post-exercise energy and macronutrient intake, appetite sensations, and food reward in healthy adults

Limited evidence is available about the variability of appetitive responses within individuals after an acute bout of exercise. The present study aimed to assess the consistency and individual variability of post-exercise appetitive responses in healthy individuals. Twenty participants (10 females, 23.9 ± 4.1 years, 22.5 ± 2.0 kg m−2) joined the laboratory to perform four sessions separated by a minimum of 5 days: i) a control session with a rest period before and an ad libitum lunch (REST), and ii) three identical exercise sessions (EX) with a 30-min moderate-intensity (60–70% of predicted maximal heart rate) walking bout ending 25 min before the ad libitum lunch. Subjective appetite sensations were assessed before and after the meal at regular intervals, and satiety quotients were calculated. Food reward was assessed by the Leeds Food Preference Questionnaire before and after lunch. For each EX session, the difference with the REST session was calculated (Δ = EX – REST). Energy and macronutrient intake were consistent in response to exercise (all intraclass correlation coefficients (ICC) > 0.8) while results showed that post-exercise subjective appetite sensations and satiety quotients varied across the three EX sessions (almost all ICC < 0.7). Food reward was overall consistent in response to exercise before the test meal but not after. When considering the changes (Δ), the results showed no or poor consistency for most of the appetitive outcomes. To conclude, energy and macronutrient intake, as well as pre-meal food reward, are consistent after exercise in healthy individuals, while subjective appetite sensations are not stable within individuals across the sessions. Regarding the variations from REST to EX sessions, the results suggest that the individual changes observed are only random day-to-day variations.

Coyotes display minimal response to Cougar scent at experimental carcass sites

Abstract Interactions among predators can have cascading impacts on communities and ecosystems. These interactions often occur around carrion, where the carrion provides a food reward, but also a risk of encountering other, potentially dominant, predators. Understanding how predators balance risk and reward at carrion, and how perceived risk changes in response to carcass origins and conditions, provides valuable insight into intraguild interactions. We investigated Coyote (Canis latrans) behavior at carrion simulated as cache sites treated with Cougar (Puma concolor) scent versus carrion used as control sites to better understand how Coyotes assess risk while feeding on carrion. Coyotes displayed similar behavior between sites treated and untreated with Cougar scent, suggesting that the presence of Cougar scent did not alter perceived risk by Coyotes in our study. Instead, Coyote behavior responded to carcass age, elevation, and whether avian scavengers had visited the carcass. Coyotes spent more time feeding, more time on camera, and touched carcasses quicker as carcass age increased. Avian scavengers appeared to compete with Coyotes, and while the presence of avian scavengers reduced time to carcass detection by Coyotes, it also decreased time spent feeding. These results suggest that carcass condition is a more important indicator of risk and reward than the presence of dominant predator scent to Coyotes. Predator scent may be an unreliable cue of immediate predator presence. Alternatively, all carcasses may be risky because dominant predators also scavenge carrion, creating similar risk regardless of previous visitation by dominant predators. These results provide insights into predator interactions and can also inform the use of scent cues in wildlife management.

The Affective Bias Test and Reward Learning Assay: Neuropsychological Models for Depression Research and Investigating Antidepressant Treatments in Rodents.

The Affective Bias Test (ABT) quantifies acute changes in affective state based on the affective biases they generate in an associative reward learning task. The Reward Learning Assay (RLA) provides a control assay for the ABT and reward-induced biases generated in this model are sensitive to changes in core affective state. Both tasks involve training animals to associate a specific digging substrate with a food reward. Animals learn to discriminate between two digging substrates placed in ceramic bowls, one rewarded and one unrewarded. In the ABT, the animal learns two independent substrate-reward associations with a fixed reward value following either an affective state or drug manipulation, or under control conditions. Affective biases generated are quantified in a choice test where the animals exhibit a bias (make more choices) for one of the substrates which is specifically related to affective state at the time of learning. The ABT is used to investigate biases generated during learning as well as modulation of biases associated with past experiences. The RLA follows a similar protocol, but the animal remains in the same affective state throughout and a reward-induced bias is generated by pairing one substrate with a higher value reward. The RLA provides a control to determine if drug treatments affect memory retrieval more generally. Studies in depression models and following environmental enrichment suggest that reward-induced biases are sensitive to core changes in affective state. Each task offers different insights into affective processing mechanisms and may help improve the translational validity of animal studies and benefit pre-clinical drug development. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Bowl digging and discrimination training Basic Protocol 2: The reward learning assay Basic Protocol 3: The affective bias test - new learning Basic Protocol 4: The affective bias test - modulation of affective biases associated with past experiences.

Ceftriaxone reverses diet-induced deficits in goal-directed control.

Obesity is associated with numerous health risks and ever-increasing rates are a significant global concern. However, despite weight loss attempts many people have difficulty maintaining weight loss. Previous studies in animals have shown that chronic access to an obesogenic diet can disrupt goal-directed behavior, impairing the ability of animals to flexibly adjust food-seeking behavior following changes in the value of earned outcomes. Changes in behavioral control have been linked to disruption of glutamate transmission in the dorsal medial striatum (DMS), a region critical for the acquisition and expression of goal-directed behavior. The goal of this study was to test whether ceftriaxone, a beta-lactam antibiotic shown elsewhere to upregulate the expression of the glutamate transporter GLT-1, would improve goal-directed control following long-term exposure to an obesogenic diet. Male and female rats were given access to either standard chow or chow plus sweetened condensed milk (SCM) for 6 weeks. Access to SCM was ended and rats received daily injections of either ceftriaxone or saline for 6 days. Rats were then trained to press a lever to earn a novel food reward and, finally, were assessed for sensitivity to outcome devaluation. Histological analyses examined changes to GLT-1 protein levels and morphological changes to astrocytes, within the DMS. We found that ceftriaxone robustly restored goal-directed behavior in animals following long-term exposure to SCM. While we did not observe changes in protein levels of GLT-1 in the DMS, we observed that SCM induced changes in the morphology of astrocytes in the DMS, and that ceftriaxone mitigated these changes. These results demonstrate that long-term access to a SCM diet impairs goal-directed behavior while also altering the morphology of astrocytes in the DMS. Furthermore, these results suggest that ceftriaxone administration can reverse the impairment of goal-directed behavior potentially through its actions on astrocytes in decision-making circuitry.

From land to water: “Sunken” T-maze for associated learning in cichlid fish

The study introduced and evaluated learning paradigms for Maylandia callainos cichlids using a modified version of the rodent T-maze, filled with tank water (the "sunken" modification). Both male and female fish underwent training in two distinct conditioning paradigms. Firstly, simple operant conditioning involved placing a food reward in either the right or left compartment. Cichlids demonstrated the ability to purposefully find the bait within 6 days of training, with a persistent place preference lasting up to 6 days. Additionally, the learning dynamics varied with sex: female cichlids exhibited reduction in latency to visit the target compartment and consume the bait, along with a decrease in the number of errors 3 and 4 days earlier than males, respectively. Secondly, visually-cued operant conditioning was conducted, with a food reward exclusively placed in the yellow compartment, randomly positioned on the left or right side of the maze during each training session. Visual learning persisted for 10 days until reaction time improvement plateaued. Color preference disappeared after 4 consecutive check-ups, with no sex-related interference. For further validation of visually-cued operant conditioning paradigm, drugs MK-801 (dizocilpine) and caffeine, known to affect performance in learning tasks, were administered intraperitoneally. Chronic MK-801 (0.17 mg/kg) impaired maze learning, resulting in no color preference development. Conversely, caffeine administration enhanced test performance, increasing precision in fish. This developed paradigm offers a viable approach for studying learning and memory and presents an effective alternative to rodent-based drug screening tools, exhibiting good face and predictive validity.

Strain and age but not maternal feeding of n-3 fatty acids affect the performance of laying hen offspring in a series of associative learning tasks

Commercial poultry are typically fed diets with fatty acid compositions that differ considerably from wild-type diets in the omega-6 to omega-3 FA ratio (n-6: n-3). Maternal dietary n-3 FA have been shown to affect offspring brain development and cognition in various avian and mammalian species. This study explored the effects of feeding egg-type layer breeders with flaxseed on the performance of their female offspring in a three-stage discrimination task. Shaver White and ISA Brown breeders were fed either a control diet (n-6: n-3 = 14.7:1) or a flaxseed-enriched diet (n-6: n-3 = 5.3:1) throughout the rearing and laying phases. At 30 and 36 weeks of age, eggs were collected, incubated and hatched. Offspring were housed in enriched floor pens and received a control diet. At 12 (pullets) and 33 (hens) weeks of age, three learning tasks were conducted: behavioural shaping (N=437), discrimination test (N=350), and reversal learning (N=213). Food rewards (sweetcorn and raisins) were placed in the “reward” cup. Behavioural shaping consisted of five phases (P): P1 clear cup, P2 coloured cup, P3 coloured cup half-covered with a lid, P4 coloured cup three quarter covered with a lid, and P5 coloured cup covered with a lid. One cup, alternating between blue and green, was presented. Chickens had to eat the food reward from the cup in 4/5 trials to pass each phase. Two cups (green and blue) were presented during discrimination testing and reversal learning with food only in the predetermined “reward” cup. Learning criterion was choosing the correct cup in 4/5 trials for three consecutive days in discrimination testing and for two consecutive days in reversal learning. Data were analysed using survival class analyses. The hazard ratio (HR), 95% confidence intervals (CI) [LL, UL] and p-values to determine the probability of reaching learning criteria are reported. In P1 of behavioural shaping, Brown hens were likelier to reach criteria (HR=2.28, 95% CI [1.48, 3.55], p<0.001). For overall success in behavioural shaping (P1–5), hens were likelier to reach criteria than pullets (HR=2.42, 95% CI [1.50, 3.91], p<0.001). White chickens were likelier to reach criteria in the discrimination test than Brown chickens (HR=1.03, 95% CI [1.01, 1.75], p=0.04). Finally, pullets were likelier to reach criteria in reversal learning than hens (HR=0.44, 95% CI [0.23, 0.86], p=0.016). These results show that age, strain, and their interaction, but not maternal n-3 FA diet, affected the success of chickens in learning tasks.

Relationship between energy balance and reward system gene polymorphisms and appetitive traits in young Mexican subjects.

Appetitive traits are influenced by the interplay between genetic and environmental factors. This study aimed to explore the relationship between gene polymorphisms involved in the regulation of energy balance and food reward and appetitive traits in young Mexican subjects. This cross-sectional study involved 118 university freshman undergraduates who completed the Adult Eating Behaviour Questionnaire for Spanish speakers (AEBQ-Esp) to assess their appetitive traits. A real-time PCR system was employed to determine gene polymorphisms involved in energy balance (LEP rs7799039, MC4R rs17782313, FTO rs9939609, GHRL rs696217), and reward system (DRD2/ANKK1 Taq1A rs1800497 and COMT rs4680). The mean age of participants was 20.14 ± 3.95 years, 71.2% were women and their mean BMI was 23.52 ± 4.05 kg/m2. COMT Met allele carriers presented a significantly higher "Emotional overeating" mean score than Val allele carriers (2.63 ± 0.70 vs. 2.23 ± 0.70, p = 0.028). The MC4R CC + CT genotype correlated positively with "Emotional overeating" (Phi = 0.308, p = 0.01). The COMT MetMet+MetVal genotype correlated with higher "Emotional overeating" (r = 0.257, p = 0.028; Phi = 0.249, p = 0.033). The protective genotype FTO TT correlated positively with "Emotional undereating" (Phi = 0.298, p = 0.012). Carriers of the risk genotype MC4R CC + CT presented a higher risk of "Emotional overeating" than TT carriers (OR = 2.4, 95% CI 1.3-4.8, p = 0.034). Carriers of the risk genotype COMT MetMet+MetVal (OR = 3.4, 95% CI 1.1-10.3, p = 0.033), were associated with a higher risk of "Emotional overeating" than ValVal carriers. The protective FTO genotype TT was associated with "Emotional undereating" (OR = 1.8, 95% CI 1.1-9.1, p = 0.014). The study found a relationship between the protective genotypes of FTO TT and "Emotional undereating" and risk genotypes of COMT Met/Met+Met/Val and MC4R CC + CT with "Emotional overeating." These genetic factors may increase weight gain by enhancing hedonic food consumption and reducing satiety control. Future studies should focus on replication studies in ethnically diverse young adults and life stages to explore the relationship between polymorphisms and appetitive traits and weight. This will help tailor personalized nutrigenetic strategies to counteract disordered eating patterns leading to obesity and associated co-morbidities.

Going back to "basics": Harlow's learning set task with wolves and dogs.

To survive and reproduce, animals need to behave adaptively by adjusting their behavior to their environment, with learning facilitating some of these processes. Dogs have become a go-to model species in comparative cognition studies, making our understanding of their learning skills paramount at multiple levels, not only with regards to basic research on their cognitive skills and the effects of domestication, but also with applied purposes such as training. In order to tackle these issues, we tested similarly raised wolves and dogs in a serial learning task inspired by Harlow's "learning set." In Phase 1, different pairs of objects were presented to the animals, one of which was baited while the other was not. Both species' performance gradually improved with each new set of objects, showing that they "learnt to learn," but no differences were found between the species in their learning speed. In Phase 2, once subjects had learned the association between one of the objects and the food reward, the contingencies were reversed and the previously unrewarded object of the same pair was now rewarded. Dogs' performance in this task seemed to be better than wolves', albeit only when considering just the first session of each reversal, suggesting that the dogs might be more flexible than wolves. Further research (possibly with the aid of refined methods such as computer-based tasks) would help ascertain whether these differences between wolves and dogs are persistent across different learning tasks.

Functional alterations in overweight/obesity: focusing on the reward and executive control network.

Overweight (OW) and obesity (OB) have become prevalent issues in the global public health arena. Serving as a prominent risk factor for various chronic diseases, overweight/obesity not only poses serious threats to people's physical and mental health but also imposes significant medical and economic burdens on society as a whole. In recent years, there has been a growing focus on basic scientific research dedicated to seeking the neural evidence underlying overweight/obesity, aiming to elucidate its causes and effects by revealing functional alterations in brain networks. Among them, dysfunction in the reward network (RN) and executive control network (ECN) during both resting state and task conditions is considered pivotal in neuroscience research on overweight/obesity. Their aberrations contribute to explaining why persons with overweight/obesity exhibit heightened sensitivity to food rewards and eating disinhibition. This review centers on the reward and executive control network by analyzing and organizing the resting-state and task-based fMRI studies of functional brain network alterations in overweight/obesity. Building upon this foundation, the authors further summarize a reward-inhibition dual-system model, with a view to establishing a theoretical framework for future exploration in this field.

The potential use of daridorexant in eating disorders: beyond the treatment of insomnia?

A strong interplay exists between sleep and dietary habits, and sleep disturbances have been repeatedly documented in individuals with eating disorders (EDs). The orexin system - implicated in sleep regulation, energy homeostasis, and food reward - may represent a mechanist link between sleep alterations and disordered eating behaviors. Daridorexant is a dual orexin receptor antagonist (DORA) recently approved for the treatment of insomnia, with demonstrated efficacy and tolerability. Owing to its action on orexin neurons, the compound represents an intriguing option for addressing both sleep-related and core symptoms of EDs. By inhibiting motor hyperactivity, daridorexant may reduce excessive physical exercise in individuals with anorexia nervosa (AN) restricting type. Additionally, the compound may exert anti-binge effects, suggesting broad applicability in binge ED, bulimia nervosa, and binge/purging AN. In this framework, daridorexant emerges as a promising therapeutic option, offering a multifaceted approach to improving circadian rhythms, energy balance, and overall quality of life in individuals with diverse ED subtypes.

Loss of glycine receptors in the nucleus accumbens and ethanol reward in an Alzheimer´s Disease mouse model

Alterations in cognitive and non-cognitive cerebral functions characterize Alzheimer's disease (AD). Cortical and hippocampal impairments related to extracellular accumulation of Aβ in AD animal models have been extensively investigated. However, recent reports have also implicated intracellular Aβ in limbic regions, such as the nucleus accumbens (nAc). Accumbal neurons express high levels of inhibitory glycine receptors (GlyRs) that are allosterically modulated by ethanol and have a role in controlling its intake. In the present study, we investigated how GlyRs in the 2xTg mice (AD model) affect nAc functions and ethanol intake behavior. Using transgenic and control aged-matched litter mates, we found that the GlyRα2 subunit was significantly decreased in AD mice (6-month-old). We also examined intracellular calcium dynamics using the fluorescent calcium protein reporter GCaMP in slice photometry. We also found that the calcium signal mediated by GlyRs, but not GABAAR, was also reduced in AD neurons. Additionally, ethanol potentiation was significantly decreased in accumbal neurons in the AD mice. Finally, we performed drinking in the dark (DID) experiments and found that 2xTg mice consumed less ethanol on the last day of DID, in agreement with a lower blood ethanol concentration. 2xTg mice also showed lower sucrose consumption, indicating that overall food reward was altered. In conclusion, the data support the role of GlyRs in nAc neuron excitability and a decreased glycinergic activity in the 2xTg mice that might lead to impairment in reward processing at an early stage of the disease.

Differential effects of acute and prolonged morphine withdrawal on motivational and goal-directed control over reward-seeking behaviour.

Opioid addiction is a relapsing disorder marked by uncontrolled drug use and reduced interest in normally rewarding activities. The current study investigated the impact of spontaneous withdrawal from chronic morphine exposure on emotional, motivational and cognitive processes involved in regulating the pursuit and consumption of food rewards in male rats. In Experiment 1, rats experiencing acute morphine withdrawal lost weight and displayed somatic signs of drug dependence. However, hedonically driven sucrose consumption was significantly elevated, suggesting intact and potentially heightened reward processing. In Experiment 2, rats undergoing acute morphine withdrawal displayed reduced motivation when performing an effortful response for palatable food reward. Subsequent reward devaluation testing revealed that acute withdrawal disrupted their ability to exert flexible goal-directed control over reward seeking. Specifically, morphine-withdrawn rats were impaired in using current reward value to select actions both when relying on prior action-outcome learning and when given direct feedback about the consequences of their actions. In Experiment 3, rats tested after prolonged morphine withdrawal displayed heightened rather than diminished motivation for food rewards and retained their ability to engage in flexible goal-directed action selection. However, brief re-exposure to morphine was sufficient to impair motivation and disrupt goal-directed action selection, though in this case, rats were only impaired in using reward value to select actions in the presence of morphine-paired context cues and in the absence of response-contingent feedback. We suggest that these opioid-withdrawal induced deficits in motivation and goal-directed control may contribute to addiction by interfering with the pursuit of adaptive alternatives to drug use.

Refocusing the Debate: Our Original Critiques of Koops et al. (2022) Still Stand

Koops et al. (2022, 2023) claim that an experimental field study (Koops et al., 2022) provided valid evidence against a latent solution explanation for chimpanzee (Pan troglodytes verus) nut cracking know-how in the wild. In our previous response (Tennie &amp; Call, 2023) we identified two major problems with this interpretation. First, Koops et al. (2022) study subjects were clearly unmotivated to access the intended food reward (nut kernels) – rendering the secondary question of whether they would use tools to crack the provided nuts to access these kernels a moot point. Second, only one of the subjects who came into contact with the experimental setup was within the chimpanzee most sensitive learning bracket to develop nut cracking (identified in previous field studies; Matsuzawa, 1994, 1996; Biro et al., 2003). We concluded that Koops et al.’s (2022) study failed to provide valid evidence against the zone of latent solution hypothesis as applied to chimpanzee nut cracking in the wild. In their reply, Koops et al. (2023) argued against both our critiques. Here, we refocus the debate, reiterate our arguments and provide further evidence that invalidate Koops et al. (2022) conclusion that “nut cracking falls outside” the zone of latent solutions of wild chimpanzees. We end with a call for more data.

321. Reward Learning Bias for Food Rewards in Binge-Eating Disorder

321. Reward Learning Bias for Food Rewards in Binge-Eating Disorder