Food reinforcement and habituation to food are processes related to initiation and cessation of eating

Behavioral separation of liking and wanting in response to olfactory and visual food cues

In real-world settings, food rewards are processed in parallel across several sensory modalities, but paradigms that compare contributions of different modalities are lacking. While odor perception in particular is frequently implicated in appetite regulation, the mechanisms by which food odors differentially evoke experiences of wanting and liking remain poorly understood. This study addressed this gap by dissociating liking from wanting responses for olfactory stimuli, and establishing commonalities and differences relative to the visual modality. In two separate experiments, participants (n1=37, n2=43) rated content-matched batteries of odors and pictures, respectively, for their ability to elicit pleasure (liking) and the desire to eat (wanting). A third experiment (n3=39) utilized a combined olfactory-visual paradigm to test the separation of these dimensions in a multisensory context. Our results show that participants differentiated clearly and reliably between liking and wanting for both odors and pictures, as demonstrated by a high difference score between the two in non-food (high liking, low wanting), but not in food (both high) or disgusting stimuli (both low), and high within-session retest reliability. Higher variability for olfactory relative to visual assessments was observed and likely reflects well-established difficulties with odor object identification. Taken together, our study demonstrates that olfactory stimuli can be used in experimental settings to evoke separable experiences of liking and wanting for food and non-food stimuli. Manipulating these components independently across sensory modalities in experimental studies could generate novel insights into how olfactory and visual cues differentially contribute to anticipatory and consummatory food reward processing, in healthy and disordered eating.

Responsiveness and Reliability of a Sipping Device to Measure Motivation in Normal-Weight Individuals and Bariatric Surgery Patients

There is an urgent need to measure the motivation to taste a sweet fluid in order to determine the influence of sweet tastes on the potential choices and consumption of beverages in patients with obesity. Current methods utilize either survey instruments or arbitrary operant tasks. The sipometer enables the participant to utilize an actual ingestive behavioral response to measure motivation during access to beverages on either ad libitum (AL) or progressive time ratio (PR) schedules. We determined the sipometer's responsiveness and reliability as a test of change in motivation for sweet tastes after bariatric surgery. Participants (58 patients and 28 controls, BMI: 18.5-24.9 kg/m2) sham-consumed an aspartame-sweetened (S) and non-sweetened (N) beverage under AL and PR schedules at a pre-surgery/baseline and a 3-month and 24-month visit (patients only). Cumulative pressure (CumPres), a measure of effort, was the sum of the pressures exerted during sipping under each condition. Baseline CumPres for PRS was higher than ALS and ALN in patients (p < 0.03) and higher than PRN in controls (p = 0.009). At 3 months, CumPres did not differ amongst conditions in patients, but CumPres for PRS was higher than all other conditions in controls (p < 0.0005). There were no baseline group differences; however, patients' CumPres for PRS was lower than controls' at 3 months (p = 0.002). Patients' CumPres for PRS decreased non-significantly between the baseline and 3 months but increased at 24 months compared to 3 months (p = 0.025) and was no different from baseline. Controls' CumPres for PRS increased at 3 months (p = 0.0359), but CumPres for all conditions was correlated between visits (p's < 0.038). The sipometer is a reliable and sensitive measure of motivation to consume sweet beverages and may reflect changes in post-operative energy intake.

Mechanisms underlying fNIRS-neurofeedback over the prefrontal cortex for participants with binge-eating disorder

OBJECTIVE

Despite the increasing popularity of neurofeedback (NF), aiming at voluntary modulation of dysfunctional prefrontal cortex (PFC) signals in the treatment of binge-eating disorder (BED) and/or overweight, mechanisms remain poorly understood.

METHODS

Based on a randomized-controlled trial offering 12 food-specific real-time functional near-infrared spectroscopy (rtfNIRS)-NF sessions to participants with BED (n = 22), this preregistered study examined (1) online regulation success as predictor for offline regulation success, defined by PFC signals during regulation versus watch, and subjective regulation success, and (2) changes in loss of control (LOC) eating after vs. before and across 12 rtfNIRS-NF-sessions.

RESULTS

Higher online regulation success expectedly predicted better subjective, but worse offline regulation success. LOC eating decreased after vs. before, but not over rtfNIRS-NF-sessions, and was not associated with subjective or offline regulation success.

CONCLUSIONS

The association between online and subjective regulation success confirmed the presumed mechanism of operant conditioning underlying rtfNIRS-NF-learning. The contrary association between online and offline regulation indicated differential PFC involvement upon subtraction of automatic food-specific responses from regulation signals for offline success. Decreased LOC eating after food-specific rtfNIRS-NF-sessions suggested the potential of NF in BED treatment.

SIGNIFICANCE

Results may guide the optimization of future NF studies in larger samples with BED.

Transcranial Magnetic Stimulation for Reducing the Relative Reinforcing Value of Food in Adult Patients With Obesity Pursuing Metabolic and Bariatric Surgery: Protocol for a Pilot, Within-Participants, Sham-Controlled Trial

BACKGROUND

Metabolic and bariatric surgery (MBS) is the most effective and durable obesity treatment. However, there is heterogeneity in weight outcomes, which is partially attributed to variability in appetite and eating regulation. Patients with a strong desire to eat in response to the reward of palatable foods are more likely to overeat and experience suboptimal outcomes. This subgroup, classified as at risk, may benefit from repetitive transcranial magnetic stimulation (rTMS), a noninvasive brain stimulation technique that shows promise for reducing cravings and consumption of addictive drugs and food; no study has evaluated how rTMS affects the reinforcing value of food and brain reward processing in the context of MBS.

OBJECTIVE

The goal of the Transcranial Magnetic Stimulation to Reduce the Relative Reinforcing Value of Food (RESTRAIN) study is to perform an initial rTMS test on the relative reinforcing value (RRV) of food (the reinforcing value of palatable food compared with money) among adult patients who are pursuing MBS and report high food reinforcement. Using a within-participants sham-controlled crossover design, we will compare the active and sham rTMS conditions on pre- to posttest changes in the RRV of food (primary objective) and the neural modulation of reward, measured via electroencephalography (EEG; secondary objective). We hypothesize that participants will show larger decreases in food reinforcement and increases in brain reward processing after active versus sham rTMS.

METHODS

Participants (n=10) will attend 2 study sessions separated by a washout period. They will be randomized to active rTMS on 1 day and sham rTMS on the other day using a counterbalanced schedule. For both sessions, participants will arrive fasted in the morning and consume a standardized breakfast before being assessed on the RRV of food and reward tasks via EEG before and after rTMS of the left dorsolateral prefrontal cortex.

RESULTS

Recruitment and data collection began in December 2022. As of October 2023, overall, 52 patients have been screened; 36 (69%) screened eligible, and 17 (47%) were enrolled. Of these 17 patients, 3 (18%) were excluded before rTMS, 5 (29%) withdrew, 4 (24%) are in the process of completing the protocol, and 5 (29%) completed the protocol.

CONCLUSIONS

The RESTRAIN study is the first to test whether rTMS can target neural reward circuits to reduce behavioral (RRV) and neural (EEG) measures of food reward in patients who are pursuing MBS. If successful, the results would provide a rationale for a fully powered trial to examine whether rTMS-related changes in food reinforcement translate into healthier eating patterns and improved MBS outcomes. If the results do not support our hypotheses, we will continue this line of research to evaluate whether additional rTMS sessions and pulses as well as different stimulation locations produce clinically meaningful changes in food reinforcement.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05522803; https://clinicaltrials.gov/study/NCT05522803.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/50714.

A preliminary evaluation of habituation and dishabituation of operant responding in mice

Previous research has suggested that operant response decrements within experimental sessions are due in part to habituation to the repeated presentation of reinforcers. One way to assess the role of habituation in within-session response decrements is to conduct a test for dishabituation, a phenomenon in which a habituated response to a given stimulus recovers following the presentation of some strong or novel stimulus other than the habituated stimulus. Dishabituation of operant responding has been demonstrated on several occasions in the literature, but studies with non-human subjects have thus far been limited to those using rats and pigeons. Two experiments attempting to replicate these findings with mice were conducted. Two groups of mice nose-poked for a sweetened condensed milk/water reinforcer on either a fixed-ratio 4 or variable-interval 15 s schedule of reinforcement. During testing, baseline sessions were then alternated with two test conditions and a control condition. Test conditions included a 5 s auditory stimulus or flashing of the house light presented mid-session. Control conditions were identical to baseline. Dishabituation was not observed for either group in Experiment 1. In Experiment 2, dishabituation was not observed for the fixed-ratio 4 group but was observed for the variable interval 15 s group. Considerations for further study of operant dishabituation in mice are discussed.

Late-stage Attentional Bias towards Food Cues Varies According to Weight Status

The Current food environment has become increasingly obesogenic, with rates of obesity and related conditions continually rising. Advertisements for energy-dense foods are abundant and promote unhealthy eating behaviors by capitalizing on one's attentional bias towards food cues, a cognitive process resulting from the sensitization of highly reinforcing food. A heightened awareness towards food cues may promote overconsumption of energy-dense foods. The current study employed novel eye-tracking methodology to capture sustained, or late-stage, attentional bias towards food cues. Late-stage attentional bias is the aspect of attentional bias under conscious control and likely more prone to modification compared to initial/ early-stage attentional bias, which reflects automatic processes. The present study hypothesized late-stage attentional bias towards food cues is greater among individuals classified as overweight/obese than those classified as normal weight. Thirty (30) participants classified as overweight/obese (BMI ≥25) and 47 classified as normal weight (BMI <25) were assessed for late-stage attentional bias towards food cues, conceptualized as the percentage of time fixated on food cues when both food and neutral images were presented during a food-specific visual probe procedure task. Percentage of time fixated on food cues was 51.25 ± 1.27 (mean + SE) among individuals classified as overweight to obese while those classified as normal weight had a percent fixation of 47.26 ± 0.87 (P=0.03). In conclusion, individuals classified as overweight to obese have greater late-stage attentional bias towards food cues. This establishes an important factor influencing energy intake that may be modified in future clinical trials.

Nucleus Accumbens D1 Receptor-Expressing Spiny Projection Neurons Control Food Motivation and Obesity

BACKGROUND

Obesity is a chronic relapsing disorder that is caused by an excess of caloric intake relative to energy expenditure. There is growing recognition that food motivation is altered in people with obesity. However, it remains unclear how brain circuits that control food motivation are altered in obese animals.

METHODS

Using a novel behavioral assay that quantifies work during food seeking, in vivo and ex vivo cell-specific recordings, and a synaptic blocking technique, we tested the hypothesis that activity of circuits promoting appetitive behavior in the core of the nucleus accumbens (NAc) is enhanced in the obese state, particularly during food seeking.

RESULTS

We first confirmed that mice made obese with ad libitum exposure to a high fat diet work harder than lean mice to obtain food, consistent with an increase in food motivation in obese mice. We observed greater activation of D₁ receptor-expressing NAc spiny projection neurons (NAc D1^SPNs) during food seeking in obese mice relative to lean mice. This enhanced activity was not observed in D₂ receptor-expressing neurons (D2^SPNs). Consistent with these in vivo findings, both intrinsic excitability and excitatory drive onto D1^SPNs were enhanced in obese mice relative to lean mice, and these measures were selective for D1^SPNs. Finally, blocking synaptic transmission from D1^SPNs, but not D2^SPNs, in the NAc core decreased physical work during food seeking and, critically, attenuated high fat diet-induced weight gain.

CONCLUSIONS

These experiments demonstrate the necessity of NAc core D1^SPNs in food motivation and the development of diet-induced obesity, establishing these neurons as a potential therapeutic target for preventing obesity.

Children's eating behaviours and related constructs: conceptual and theoretical foundations and their implications

BACKGROUND

There is a substantial body of research on children's eating behaviours (e.g., food responsiveness and fussiness) and related constructs (e.g., eating in the absence of hunger, appetite self-regulation). This research provides a foundation for understanding children's dietary intakes and healthy eating behaviours, as well as efforts at intervention, whether in relation to food avoidance, overeating and/or trajectories to excess weight gain. The success of these efforts and their associated outcomes is dependent on the theoretical foundation and conceptual clarity of the behaviours and constructs. This, in turn contributes to the coherence and precision of the definitions and measurement of these behaviours and constructs. Limited clarity in these areas ultimately creates uncertainty around the interpretation of findings from research studies and intervention programs. At present there does not appear to be an overarching theoretical framework of children's eating behaviours and associated constructs, or for separate domains of children's eating behaviours/constructs. The main purpose of the present review was to examine the possible theoretical foundations of some of the main current questionnaire and behavioural measures of children's eating behaviours and related constructs.

METHODS

We reviewed the literature on the most prominent measures of children's eating behaviours for use with children aged ~ 0-12 years. We focused on the explanations and justifications for the original design of the measures and whether these included theoretical perspectives, as well as current theoretical interpretations (and difficulties) of the behaviours and constructs.

RESULTS

We found that the most commonly used measures had their foundations in relatively applied or practical concerns rather than theoretical perspectives.

CONCLUSIONS

We concluded, consistent with Lumeng & Fisher (1), that although existing measures have served the field well, to advance the field as a science, and better contribute to knowledge development, increased attention should be directed to the conceptual and theoretical foundations of children's eating behaviours and related constructs. Suggestions for future directions are outlined.

Psychometric properties of the Eating in the Absence of Hunger Questionnaire in treatment-seeking adults with overweight and obesity

Understanding eating behaviors that contribute to overweight and obesity (OW/OB) is an important public health objective. One eating behavior known to contribute to overeating is eating in the absence of hunger (EAH). The Eating in the Absence of Hunger Questionnaire for Children was developed to assess external events and internal experiences that lead children to overeat. Despite the measure's adaptation for use with adults (i.e., EAH-A), its psychometric properties within this population have not been explored. This study assessed the psychometric properties of the EAH-A in sample of 311 treatment-seeking adults with OW/OB (mean BMI = 34.5 [5.1]; mean age = 46.3 [12.1]; 81.7% female; 20.6% Latinx, 59.2% white). The EAH-A contains 14 items and assesses three domains: negative affect eating (EAH-NAE), external eating, and fatigue/boredom eating, through two parallel sets of items assessing initiating EAH and continuing EAH. Exploratory Factor Analysis was performed with promax rotation and maximum likelihood factor extraction. Results supported a unitary factor of EAH, with scale responses driven by EAH-NAE items. Results may be explained in part by scale structure and domain imbalance favoring EAH-NAE items, or the true internal structure of EAH may consist of a singular latent construct. Follow-up analyses indicated redundancy of the scale's parallel sections. If researchers are primarily interested in EAH-NAE, only the three "start eating" or "keep eating" items may be needed. This study highlights the importance of validating the psychometric properties of a measure within intended populations to ensure interpretations are valid.

Valuing the Diversity of Research Methods to Advance Nutrition Science

The ASN Board of Directors appointed the Nutrition Research Task Force to develop a report on scientific methods used in nutrition science to advance discovery, interpretation, and application of knowledge in the field. The genesis of this report was growing concern about the tone of discourse among nutrition professionals and the implications of acrimony on the productive study and translation of nutrition science. Too often, honest differences of opinion are cast as conflicts instead of areas of needed collaboration. Recognition of the value (and limitations) of contributions from well-executed nutrition science derived from the various approaches used in the discipline, as well as appreciation of how their layering will yield the strongest evidence base, will provide a basis for greater productivity and impact. Greater collaborative efforts within the field of nutrition science will require an understanding that each method or approach has a place and function that should be valued and used together to create the nutrition evidence base. Precision nutrition was identified as an important emerging nutrition topic by the preponderance of task force members, and this theme was adopted for the report because it lent itself to integration of many approaches in nutrition science. Although the primary audience for this report is nutrition researchers and other nutrition professionals, a secondary aim is to develop a document useful for the various audiences that translate nutrition research, including journalists, clinicians, and policymakers. The intent is to promote accurate, transparent, verifiable evidence-based communication about nutrition science. This will facilitate reasoned interpretation and application of emerging findings and, thereby, improve understanding and trust in nutrition science and appropriate characterization, development, and adoption of recommendations.

Integrative Hedonic and Homeostatic Food Intake Regulation by the Central Nervous System: Insights from Neuroimaging

Food intake regulation in humans is a complex process controlled by the dynamic interaction of homeostatic and hedonic systems. Homeostatic regulation is controlled by appetitive signals from the gut, adipose tissue, and the vagus nerve, while conscious and unconscious reward processes orchestrate hedonic regulation. On the one hand, sight, smell, taste, and texture perception deliver potent food-related feedback to the central nervous system (CNS) and influence brain areas related to food reward. On the other hand, macronutrient composition stimulates the release of appetite signals from the gut, which are translated in the CNS into unconscious reward processes. This multi-level regulation process of food intake shapes and regulates human ingestive behavior. Identifying the interface between hormones, neurotransmitters, and brain areas is critical to advance our understanding of conditions like obesity and develop better therapeutical interventions. Neuroimaging studies allow us to take a glance into the central nervous system (CNS) while these processes take place. This review focuses on the available neuroimaging evidence to describe this interaction between the homeostatic and hedonic components in human food intake regulation.

Sucrose solution concentration and the intermittent access induced consumption increase

Animals fed ad libitum consume less of a preferred additional food with daily access than with access only once every few days. With 4% sucrose solution, rats can drink over twice as much in a day if they receive it every fourth day compared to daily access. These differences are maintained when all rats are put on the same schedule. We explored the intermittency effect with 1, 4, 8, and 16% sucrose solutions available for 23 h daily or every third day in adult male rats. The consumption difference was only evident with the 4% solution. In a second experiment with a 16% solution, only a small difference was seen in the first phase. When the sucrose concentration was lowered to 4% in a second phase with alternate day access, the rats with prior every third-day access showed an immediate, pronounced elevation in consumption compared to rats with initial daily access. These results suggest that intermittency induces a long-lasting elevation in the sucrose solution's value for rats, but it may only be evident under the appropriate testing conditions. The relevance of this increased consumption for understanding human obesity and binge eating is discussed.