How partial reinforcement of food cues affects the extinction and reacquisition of appetitive responses. A new model for dieting success?

Habituation or sensitization of brain response to food cues: Temporal dynamic analysis in an functional magnetic resonance imaging study

Introduction

In the modern obesogenic environment, heightened reactivity to food-associated cues plays a major role in overconsumption by evoking appetitive responses. Accordingly, functional magnetic resonance imaging (fMRI) studies have implicated regions of the salience and rewards processing in this dysfunctional food cue-reactivity, but the temporal dynamics of brain activation (sensitization or habituation over time) remain poorly understood.

Methods

Forty-nine obese or overweight adults were scanned in a single fMRI session to examine brain activation during the performance of a food cue-reactivity task. A general linear model (GLM) was used to validate the activation pattern of food cue reactivity in food > neutral contrast. The linear mixed effect models were used to examine the effect of time on the neuronal response during the paradigm of food cue reactivity. Neuro-behavioral relationships were investigated with Pearson's correlation tests and group factor analysis (GFA).

Results

A linear mixed-effect model revealed a trend for the time-by-condition interactions in the left medial amygdala [t(289) = 2.21, β = 0.1, P = 0.028], right lateral amygdala [t(289) = 2.01, β = 0.26, P = 0.045], right nucleus accumbens (NAc) [t(289) = 2.81, β = 0.13, P = 0.005] and left dorsolateral prefrontal cortex (DLPFC) [t(289) = 2.58, β = 0.14, P = 0.01], as well as in the left superior temporal cortex [42 Area: t(289) = 2.53, β = 0.15, P = 0.012; TE1.0_TE1.2 Area: t(289) = 3.13, β = 0.27, P = 0.002]. Habituation of blood-oxygenation-level-dependent (BOLD) signal during exposure to food vs. neutral stimuli was evident in these regions. We have not found any area in the brain with significant increased response to food-related cues over time (sensitization). Our results elucidate the temporal dynamics of cue-reactivity in overweight and obese individuals with food-induced craving. Both subcortical areas involved in reward processing and cortical areas involved in inhibitory processing are getting habituated over time in response to food vs. neutral cues. There were significant bivariate correlations between self-report behavioral/psychological measures with individual habituation slopes for the regions with dynamic activity, but no robust cross-unit latent factors were identified between the behavioral, demographic, and self-report psychological groups.

Discussion

This work provides novel insights into dynamic neural circuit mechanisms supporting food cue reactivity, thereby suggesting pathways in biomarker development and cue-desensitization interventions.

Avoidance in Anorexia Nervosa: Towards a research agenda

Anorexia Nervosa is a severe and disabling mental disorder and a huge challenge to treat. Intense fears of e.g., food, eating, weight gain and social evaluation are core features of anorexia nervosa and obstacles during treatment. The perceived threats trigger avoidance and safety behaviors like highly restrictive eating, strict eating rules, vomiting and body checking, to minimize feared outcomes. The role of avoidance in anorexia nervosa is however hardly studied experimentally. In the present article, the focus is on a new transdiagnostic research agenda featuring both basic and clinical experimental research into avoidance as a most important mechanism maintaining the eating disorder. Avoidance learning and the generalization of learned avoidance behaviors are discussed, as well as safety behaviors and the need for inhibitory learning as a treatment target during exposure therapy.

Sensory cue reactivity: Sensitization in alcohol use disorder and obesity

Neuroimaging techniques to measure the function of the human brain such as electroencephalography (EEG), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI), are powerful tools for understanding the underlying neural circuitry associated with alcohol use disorder (AUD) and obesity. The sensory (visual, taste and smell) paradigms used in neuroimaging studies represent an ideal platform to investigate the connection between the different neural circuits subserving the reward/executive control systems in these disorders, which may offer a translational mechanism for novel intervention predictions. Thus, the current review provides an integrated summary of the recent neuroimaging studies that have applied cue-reactivity paradigms and neuromodulation strategies to explore underlying alterations in neural circuitry as well in treatment strategies in AUD and obesity. Finally, we discuss literature on mechanisms associated with increased alcohol sensitivity post-bariatric surgery (BS) which offers guidance for future research to use sensory percepts in elucidating the relation of reward signaling in AUD development post-BS.

Individual differences in extinction learning predict weight loss after treatment: A pilot study

Learning theorists suggest extinction learning to be a central mechanism in weight loss success; however, empirical studies are scarce. In this pilot study, it was examined whether individual differences in extinction learning predict outcome after weight loss treatment. Overweight and obese individuals first completed a laboratory conditioning task in which individual differences in extinction learning were assessed. Next, they were randomised to one of two weight loss interventions: cue exposure therapy (CET), which is considered the clinical analogue of laboratory extinction, or a control lifestyle intervention. In line with expectations, better extinction learning in the laboratory task was associated with more weight loss at both post-treatment (CET only) and follow-up (both interventions) measurements. In contrast, two other indices of treatment success (reduction in overeating expectancies and ad libitum food intake during a laboratory taste test) showed no associations with pre-treatment extinction learning. It is suggested that extinction learning may be a core mechanism underlying weight loss success, and hence, an important target for new obesity interventions.

Love at first taste: Activation in reward-related brain regions during single-trial naturalistic appetitive conditioning in humans

Palatable food can trigger appetitive responses, such as salivation and approach tendencies. Though evolutionarily functional, these conditioned responses can encourage overeating and obesity when food is abundant. The current study examines the neural correlates of 'denovo' Pavlovian appetitive conditioning, pairing one class of unknown objects (conditioned stimuli, CS) with their sweet taste (unconditioned stimulus, US) during a single trial. To do so, 23 participants consumed unknown (marzipan) objects of one particular color (CS+) while only interacting with control stimuli of different color and shape (CS-). After this single-trial conditioning procedure, participants viewed and rated images of the marzipan figures and the control objects during functional magnetic resonance imaging (fMRI). Relative to the CS-, the CS+ elicited stronger activation in the dorsal striatum, a brain region associated with cue-reward coupling. Furthermore, conditioning effects in subjective 'craving', defined as increased palatability and desire to eat, were observed, and these were positively related to conditioning effects in the amygdala, a brain region associated with the need-dependent value of a reward. Thus, the study identified reward-related brain regions involved in single-trial appetitive learning, thereby providing a potential mechanism that contributes to the etiology of food craving. These findings might help to understand clinically relevant food cravings in individuals with eating or weight related concerns and might support the development of extinction based treatments.

Effects of reward magnitude and training frequency on the learning rates and memory retention of the Port Jackson shark Heterodontus portusjacksoni

The development of adaptive responses to novel situations via learning has been demonstrated in a wide variety of animal taxa. However, knowledge on the learning abilities of one of the oldest extant vertebrate groups, Chondrichthyes, remains limited. With the increasing interest in global wildlife tourism and shark feeding operations, it is important to understand the capacities of these animals to form associations between human activities and food. We used an operant conditioning regime with a simple spatial cognitive task to investigate the effects of reinforcement frequency and reward magnitude on the learning performance and memory retention of Port Jackson sharks (Heterodontus portusjacksoni). Twenty-four Port Jackson sharks were assigned one of four treatments differing in reward magnitude and reinforcement frequency (large magnitude-high frequency; large magnitude-low frequency; small magnitude-high frequency; small magnitude-low frequency). The sharks were trained over a 21-day period to compare the number of days that it took to learn to pass an assigned door to feed. Sharks trained at a high reinforcement frequency demonstrated faster learning rates and a higher number of passes through the correct door at the end of the trials, while reward magnitude had limited effects on learning rate. This suggests that a reduction in reinforcement frequency during tourism-related feeding operations is likely to be more effective in reducing the risk of sharks making associations with food than limiting the amount of food provided.

Exposure therapy vs lifestyle intervention to reduce food cue reactivity and binge eating in obesity: A pilot study

BACKGROUND AND OBJECTIVES

Learning models of overeating predict that exposure therapy is effective in reducing food cue reactivity and overeating. This pilot study tested an eight-session exposure therapy aimed at inhibitory learning vs. an active control condition aimed at lifestyle improvement for obesity (treatment-as-usual). Main outcomes are snacking behavior, eating psychopathology, food cue reactivity, and weight loss. Change in overeating expectancies was assessed as mediator for outcomes, and the associations between habituation of eating desires and outcomes were investigated in the exposure condition. Sleep quality was investigated as moderator for outcomes.

METHODS

45 overweight women were randomly assigned to the exposure intervention or control condition. The main outcomes, overeating expectancies and sleep quality were re-assessed at post-treatment and three-month follow-up. Habituation of eating desires was measured during exposure sessions.

RESULTS

Compared to the control intervention, exposure led to a significantly stronger reduction in snacking behavior of exposed foods, though this effect did not generalize to non-exposed foods, and stronger binge eating frequency. The exposure condition lost significantly more weight at post-treatment and follow-up than the lifestyle condition. Changes of expectancies mediated the effect of condition on kcal consumption of exposed foods, while habituation during exposure was not related to better treatment outcome. Sleep quality did not moderate the effect of condition on treatment outcome.

LIMITATIONS

Small sample size and limited follow-up period.

CONCLUSIONS

This short exposure therapy reduced snacking behavior, binge eating and weight more than a lifestyle intervention and is therefore a recommendable intervention for obesity and overeating disorders.

Neural Correlates of Food Cue Exposure Intervention for Obesity: A Case-Series Approach

Background

People with overweight have stronger reactivity (e.g., subjective craving) to food cues than lean people, and this reactivity is positively associated with food intake. Cue reactivity is a learned response that can be reduced with food cue exposure therapy.

Objectives

It was hypothesized that participants after food cue exposure therapy would show reduced neural activity in brain regions related to food cue reactivity and increased neural activity in brain regions related to inhibitory-control as compared to participants receiving a control lifestyle intervention.

Method

Neural activity of 10 women with overweight (BMI ≥ 27 kg/m²) in response to individually tailored visually presented palatable high-caloric food stimuli was examined before vs. after a cue exposure intervention (n = 5) or a control lifestyle (n = 5) intervention. Data were analyzed case-by-case.

Results

Neural responses to food stimuli were reduced in food-cue-reactivity-related brain regions after the lifestyle intervention in most participants, and generally not after the cue exposure therapy. Moreover, cue exposure did not lead to increased activity in inhibitory-control-related brain regions. However, decreased neural activity after cue exposure was found in most participants in the lateral occipital complex (LOC), which suggests a decreased visual salience of high-caloric food stimuli.

Conclusion

Receiving a cue exposure therapy did not lead to expected neural responses. As cue exposure relies on inhibitory learning mechanisms, differences in contexts (e.g., environments and food types) between the intervention setting and the scanning sessions may explain the general lack of effect of cue-exposure on neural activity.

An experimental study on spontaneous recovery of conditioned reward expectancies and instrumental responding in humans

The aim of the present study was to investigate spontaneous recovery of reward-expectancies and a reward-associated response in humans and to assess individual factors affecting spontaneous recovery. We therefore implemented an experimental procedure comprising three separate test-sessions. In the first test-session, participants underwent instrumental discrimination training to acquire a conditioned reward-associated response, in the second test-session, memory of this response was tested followed by extinction training. In the third test-session, extinction memory was assessed. Our results demonstrate spontaneous recovery of extinguished conditioned reward-associated expectancies and indicate that differential expectancies after training and extinction and impulsivity significantly predicted the magnitude of spontaneous recovery. In contrast, limited evidence for spontaneous recovery of instrumental responding was found. Given that reward-expectancies might trigger instrumental responding these findings underline the importance of developing extinction procedures that lead to more complete and less fragile long-term extinction of reward-associated responses.

Learned Overeating: Applying Principles of Pavlovian Conditioning to Explain and Treat Overeating

PURPOSE OF REVIEW

This review provides an overview of recent findings relating to the role of Pavlovian conditioning in food cue reactivity, including its application to overeating and weight loss interventions.

RECENT FINDINGS

Both in the laboratory and in real life, cue-elicited appetitive reactivity (e.g., eating desires) can be easily learned, but (long-term) extinction is more difficult. New findings suggest impaired appetitive learning in obesity, which might be causally related to overeating. The clinical analogue of extinction-cue exposure therapy-effectively reduces cue-elicited cravings and overeating. While its working mechanisms are still unclear, some studies suggest that reducing overeating expectancies is important.

SUMMARY

Pavlovian learning theory provides a still undervalued theoretical framework of how cravings and overeating can be learned and how they might be effectively tackled. Future studies should aim to elucidate inter-individual differences in Pavlovian conditioning, study ways to strengthen (long-term) extinction, and investigate the working mechanisms of cue exposure therapy.

Cue exposure therapy reduces overeating of exposed and non-exposed foods in obese adolescents

BACKGROUND AND OBJECTIVES

This study tested whether two sessions of food cue exposure therapy reduced eating in the absence of hunger (EAH), specified for exposed and non-exposed food, in overweight and obese adolescents, and whether habituation of food cue reactivity and reduced CS-US expectancies predicted a decrease in EAH.

METHODS

41 overweight adolescents (aged 12-18 years) were randomly assigned to a cue exposure intervention or a lifestyle intervention (control condition). Habituation of food cue reactivity (self-reported desire to eat and salivation) and CS-US expectancy were measured during both sessions, and EAH was measured at the end of session two.

RESULTS

Compared to the control condition, the cue exposure condition showed less EAH for the exposed food item as well as for the non-exposed food items. Larger within-session (WSH) and between-session habituation (BSH) of cue reactivity were not related to less EAH, change in CS-US expectancy was unrelated to EAH.

LIMITATIONS

The study was underpowered, and compliance to homework instructions between sessions was poor, intervention effects might have been larger when participants adhered to daily homework exercises.

CONCLUSIONS

Food cue exposure was effective to reduce EAH of exposed and non-exposed food items, indicating generalisability of the exposure effect. In line with exposure effects in anxiety disorders, habituation was not found to benefit outcome, though the present data do also not provide evidence that CS-US expectancy violation predicts EAH.

Altered appetitive conditioning in overweight and obese women

Overweight and obese individuals show increased psychological and physiological reactivity to food cues and many of them have difficulties in achieving long-term weight loss. The current study tests whether abnormalities in the learning and extinction of appetitive responses to food cues might be responsible for this. Overweight/obese and healthy weight women completed a differential appetitive conditioning task using food as rewards, while eating expectancies, eating desires, conditioned stimulus evaluations, salivation, and electrodermal responses were assessed during an acquisition and extinction phase. Results suggested reduced discriminative conditioning in the overweight/obese group, as reflected by a worse acquisition of differential eating desires and no successful acquisition of differential evaluative responses. Some evidence was also found for impaired contingency learning in overweight and obese individuals. No group differences in conditioned salivation and skin conductance responses were found and no compelling evidence for differences in extinction was found as well. In sum, the current findings indicate that overweight and obesity may be characterized by reduced appetitive conditioning. It is suggested that this could be causally related to overeating via stronger context conditioning or a tendency towards overgeneralization in overweight and obese individuals.

Acquisition of Conditioning between Methamphetamine and Cues in Healthy Humans

Environmental stimuli repeatedly paired with drugs of abuse can elicit conditioned responses that are thought to promote future drug seeking. We recently showed that healthy volunteers acquired conditioned responses to auditory and visual stimuli after just two pairings with methamphetamine (MA, 20 mg, oral). This study extended these findings by systematically varying the number of drug-stimuli pairings. We expected that more pairings would result in stronger conditioning. Three groups of healthy adults were randomly assigned to receive 1, 2 or 4 pairings (Groups P1, P2 and P4, Ns = 13, 16, 16, respectively) of an auditory-visual stimulus with MA, and another stimulus with placebo (PBO). Drug-cue pairings were administered in an alternating, counterbalanced order, under double-blind conditions, during 4 hr sessions. MA produced prototypic subjective effects (mood, ratings of drug effects) and alterations in physiology (heart rate, blood pressure). Although subjects did not exhibit increased behavioral preference for, or emotional reactivity to, the MA-paired cue after conditioning, they did exhibit an increase in attentional bias (initial gaze) toward the drug-paired stimulus. Further, subjects who had four pairings reported "liking" the MA-paired cue more than the PBO cue after conditioning. Thus, the number of drug-stimulus pairings, varying from one to four, had only modest effects on the strength of conditioned responses. Further studies investigating the parameters under which drug conditioning occurs will help to identify risk factors for developing drug abuse, and provide new treatment strategies.

Enhancing inhibitory learning to reduce overeating: Design and rationale of a cue exposure therapy trial in overweight and obese women

The prevalence of overweight and obesity has increased substantially over the last decades. Weight loss attempts in overweight individuals are common, though they seldom result in successful long-term weight loss. One very promising treatment is food cue exposure therapy, during which overweight individuals are repeatedly exposed to food-associated cues (e.g., the sight, smell and taste of high-calorie foods, overeating environments) without eating in order to extinguish cue-elicited appetitive responses to food cues. However, only few studies have tested the effectiveness of cue exposure, especially with regards to weight loss. For exposure treatment of anxiety disorders, it has been proposed that inhibitory learning is critical for exposure to be effective. In this RCT, we translated techniques proposed by Craske et al. (2014) to the appetitive domain and developed a novel cue exposure therapy for overeating aimed at maximizing inhibitory learning. The current RCT tested the effectiveness of this 8-session cue exposure intervention relative to a control intervention in 45 overweight adult (aged 18-60) females at post-treatment and 3-month follow-up, of which 39 participants completed the study. Weight loss, eating psychopathology, food cue reactivity, and snacking behaviour were studied as main treatment outcomes, and mediators and moderators of treatment effects were studied. The presented study design represents an innovative effort to provide valuable clinical recommendations for the treatment of overeating and obesity.

The Pavlovian craver: Neural and experiential correlates of single trial naturalistic food conditioning in humans

Present-day environments are replete with tempting foods and the current obesity pandemic speaks to humans' inability to adjust to this. Pavlovian processes may be fundamental to such hedonic overeating. However, a lack of naturalistic Pavlovian paradigms in humans makes translational research difficult and important parameters such as implicitness and acquisition speed are unknown. Here we present a novel naturalistic conditioning task: an image of a neutral object was conditioned to marzipan taste in a single trial procedure by asking the participant to eat the 'object' (made from marzipan). Relative to control objects, results demonstrate robust pre- to post-conditioning changes of both subjective ratings and early as well as late event related brain potentials, suggesting contributions of implicit (attentional) and explicit (motivational) processes. Naturalistic single-trial taste-appetitive conditioning is potent in humans and shapes attentional and motivational neural processes that might challenge self-regulation during exposure to tempting foods. Thus, appetitive conditioning processes might contribute to overweight and obesity.

Food cue reactivity and craving predict eating and weight gain: a meta-analytic review

According to learning-based models of behavior, food cue reactivity and craving are conditioned responses that lead to increased eating and subsequent weight gain. However, evidence supporting this relationship has been mixed. We conducted a quantitative meta-analysis to assess the predictive effects of food cue reactivity and craving on eating and weight-related outcomes. Across 69 reported statistics from 45 published reports representing 3,292 participants, we found an overall medium effect of food cue reactivity and craving on outcomes (r = 0.33, p < 0.001; approximately 11% of variance), suggesting that cue exposure and the experience of craving significantly influence and contribute to eating behavior and weight gain. Follow-up tests revealed a medium effect size for the effect of both tonic and cue-induced craving on eating behavior (r = 0.33). We did not find significant differences in effect sizes based on body mass index, age, or dietary restraint. However, we did find that visual food cues (e.g. pictures and videos) were associated with a similar effect size to real food exposure and a stronger effect size than olfactory cues. Overall, the present findings suggest that food cue reactivity, cue-induced craving and tonic craving systematically and prospectively predict food-related outcomes. These results have theoretical, methodological, public health and clinical implications.

A Cognitive Profile of Obesity and Its Translation into New Interventions

Change your lifestyle: decrease your energy intake and increase your energy expenditure, is what obesity experts tell people who need to lose weight. Though the advice might be correct, it appears to be extremely difficult to change one’s lifestyle. Unhealthy habits usually are ingrained and hard to change, especially for people with an “obese cognitive profile.” Knowledge of the cognitive mechanisms that maintain unhealthy eating habits is necessary for the development of interventions that can change behavior effectively. This paper discusses some cognitive processes that might maintain unhealthy eating habits and make healthier eating difficult, like increased food cue reactivity, weak executive skills and attention bias. An effort is also done to translate these basic scientific findings into new interventions which aim to tackle the sabotaging cognitive processes. Preliminary studies into the effectiveness of these interventions, if available, are presented.

Implications of learning theory for developing programs to decrease overeating

Childhood obesity is associated with medical and psychological comorbidities, and interventions targeting overeating could be pragmatic and have a significant impact on weight. Calorically dense foods are easily available, variable, and tasty which allows for effective opportunities to learn to associate behaviors and cues in the environment with food through fundamental conditioning processes, resulting in measurable psychological and physiological food cue reactivity in vulnerable children. Basic research suggests that initial learning is difficult to erase, and that it is vulnerable to a number of phenomena that will allow the original learning to re-emerge after it is suppressed or replaced. These processes may help explain why it may be difficult to change food cue reactivity and overeating over the long term. Extinction theory may be used to develop effective cue-exposure treatments to decrease food cue reactivity through inhibitory learning, although these processes are complex and require an integral understanding of the theory and individual differences. Additionally, learning theory can be used to develop other interventions that may prove to be useful. Through an integration of learning theory, basic and translational research, it may be possible to develop interventions that can decrease the urges to overeat, and improve the weight status of children.

Effects of occasional reinforced trials during extinction on the reacquisition of conditioned responses to food cues

BACKGROUND AND OBJECTIVES

Successful long-term dieting appears to be difficult, and part of its difficulty might be explained by processes related to classical appetitive conditioning. Increasing the speed of extinction of appetitive responses to food cues and decreasing the magnitude of returns of these responses could help increase the long-term effectiveness of weight loss attempts. Two extinction techniques hypothesized to slow down rapid reacquisition of conditioned appetitive responses were investigated: the provision of 1) occasional reinforced extinction trials (OR) and 2) unpaired unconditioned stimuli (USs) during extinction (UNP).

METHODS

After acquisition, participants (N = 90) received one of three extinction trainings: OR, UNP, or normal extinction (control), followed by a reacquisition phase. Their desire to eat, US expectancy, and salivation were measured. Effects of impulsivity on different phases of appetitive conditioning were also assessed.

RESULTS

It was found that both extinction techniques were successful in reducing the rate of reacquisition of US expectancies. Participants in the OR condition also demonstrated a slower extinction of US expectancies and desires to eat. However, the reacquisition of conditioned desires was not affected by either extinction technique. Impulsivity did not moderate responses during acquisition or extinction, but appeared to slow down the reacquisition of conditioned desires.

LIMITATIONS

US expectancies and eating desires were not completely extinguished, and a few differences in baseline responses caused difficulty in interpreting some of the findings.

CONCLUSIONS

It is concluded that the provision of occasional reinforced extinction trials and unpaired USs seem promising techniques to slow down reacquisition, but that additional studies are needed.