Habits and Persistent Food Restriction in Patients with Anorexia Nervosa: A Scoping Review.

The aetiology of anorexia nervosa (AN) presents a puzzle for researchers. Recent research has sought to understand the behavioural and neural mechanisms of these patients' persistent choice of calorie restriction. This scoping review aims to map the literature on the contribution of habit-based learning to food restriction in AN. PRISMA-ScR guidelines were adopted. The search strategy was applied to seven databases and to grey literature. A total of 35 studies were included in this review. The results indicate that the habit-based learning model has gained substantial attention in current research, employing neuroimaging methods, scales, and behavioural techniques. Food choices were strongly associated with dorsal striatum activity, and habitual food restriction based on the self-report restriction index was associated with clinical impairment in people chronically ill with restricting AN. High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) and Regulating Emotions and Changing Habits (REaCH) have emerged as potential treatments. Future research should employ longitudinal studies to investigate the time required for habit-based learning and analyse how developmental status, such as adolescence, influences the role of habits in the progression and severity of diet-related illnesses. Ultimately, seeking effective strategies to modify persistent dietary restrictions controlled by habits remains essential.

Suppression of sweet taste-related responses by plant-derived bioactive compounds and eating. Part II: A systematic review in animals.

This article, the second in a two-part series, continues the discussion on the nature of the relationship between the level of sweet taste suppression and eating behaviour, but in animal rather human subjects. In particular, the aim was to review the scientific literature on the impact that bioactive compounds that decrease oral sweet sensations have on intake, preference and physiological status in preclinical studies. This review was registered in the International Prospective Register of Systematic Reviews and conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Scottish Intercollegiate Guidelines Network and covered original papers included in Web of Science, PubMed, Scopus, Food Science Source and Food Science and technology abstracts. We identified 28 peer-reviewed English-language studies that fit the topic and met the inclusion criteria. We identified three plant species, Gymnema sylvestre, Hovenia dulcis, and Ziziphus jujuba, that possess acute sweetness-inhibitory properties. When administered orally, these plants reduced neural responses to sweet stimuli and decreased consumption. However, studies on the longer-term effects of antisweet activity remain to be conducted. Translating the valuable insights into the mechanisms underlying the relationship between sweet taste impairment and eating behaviour into practical clinical applications are discussed.

Suppression of sweet taste-related responses by plant-derived bioactive compounds and eating. Part I: A systematic review in humans.

The taste of food plays a crucial role in determining what and how much we eat. Thus, interventions that temporarily block sweet taste receptors offer a promising approach to addressing unhealthy behaviours associated with sugary foods. However, the relationship between reduced sweet taste response and food consumption remains unclear, with contradictory findings. Certain studies suggest that a diminished perception of sweetness leads to a sense of fullness and results in reduced food intake, while others suggest the opposite effect. To shed some light, our systematic review looked into the relationship between diminished sweet taste response and food consumption by examining the effects of bioactive compounds that experimentally inhibit sweetness in healthy individuals. This review was registered in the International Prospective Register of Systematic Reviews and conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Scottish Intercollegiate Guidelines Network, and covered original papers included in Web of Science, PubMed, Scopus, Food Science Source and Food Science and technology abstracts. We identified 33 peer-reviewed English-language studies that fit the topic and met the inclusion criteria. The current literature predominantly focuses on the immediate impact of oral gymnemic acids, failing to provide preliminary evidence in support of the specific threshold hypothesis, above which food consumption decreases and below which the opposite effect occurs. Additionally, there was inconsistency in the findings regarding the short-term desire to eat following sweetness inhibition. Considering the downstream effects on energy intake and their clinical applications, further research is needed to clarify both the acute within-session effects (i.e., not wanting any more now) and the longer-term effects (i.e., deciding not to start eating) linked to oral sweet-taste-suppressing compounds.

Biomimetic tissue phantoms for neurosurgical near-infrared fluorescence imaging.

Significance: Neurosurgical fluorescence imaging is a well-established clinical approach with a growing range of indications for use. However, this technology lacks effective phantom-based tools for development, performance testing, and clinician training. Aim: Our primary aim was to develop and evaluate 3D-printed phantoms capable of optically and morphologically simulating neurovasculature under fluorescence angiography. Approach: Volumetric digital maps of the circle of Willis with basilar and posterior communicator artery aneurysms, along with surrounding cerebral tissue, were generated. Phantoms were fabricated with a stereolithography printer using custom photopolymer composites, then visualized under white light and near-infrared fluorescence imaging. Results: Feature sizes of printed components were found to be within 13% of digital models. Phantoms exhibited realistic optical properties and convincingly recapitulated fluorescence angiography scenes. Conclusions: Methods identified in this study can facilitate the development of realistic phantoms as powerful new tools for fluorescence imaging.

Food Restriction in Anorexia Nervosa in the Light of Modern Learning Theory: A Narrative Review.

Improvements in the clinical management of anorexia nervosa (AN) are urgently needed. To do so, the search for innovative approaches continues at laboratory and clinical levels to translate new findings into more effective treatments. In this sense, modern learning theory provides a unifying framework that connects concepts, methodologies and data from preclinical and clinical research to inspire novel interventions in the field of psychopathology in general, and of disordered eating in particular. Indeed, learning is thought to be a crucial factor in the development/regulation of normal and pathological eating behaviour. Thus, the present review not only tries to provide a comprehensive overview of modern learning research in the field of AN, but also follows a transdiagnostic perspective to offer testable explanations for the origin and maintenance of pathological food rejection. This narrative review was informed by a systematic search of research papers in the electronic databases PsycInfo, Scopus and Web of Science following PRISMA methodology. By considering the number and type of associations (Pavlovian, goal-directed or habitual) and the affective nature of conditioning processes (appetitive versus aversive), this approach can explain many features of AN, including why some patients restrict food intake to the point of life-threatening starvation and others restrict calorie intake to lose weight and binge on a regular basis. Nonetheless, it is striking how little impact modern learning theory has had on the current AN research agenda and practice.

Epidemiologic trends of multiple sclerosis in Puerto Rico (2013-2020).

BACKGROUND: Previous studies have demonstrated higher multiple sclerosis (MS) incidence and prevalence in Puerto Rico (PR) than in other Caribbean and Latin American countries. Our objectives are to update the epidemiologic trends in MS incidence and prevalence rates for PR from 2017 through 2020 and compare them to prior rate data from 2013 to 2016. METHODS: We used the Puerto Rico MS Foundation's registry (PRMS Registry) data to identify all newly diagnosed MS cases between January 2017 and December 2020. The study population included 568 MS patients, 406 women and 162 men living in PR. All individuals were 18 years and older and met the 2017 revised McDonald criteria for MS diagnosis. In addition, age- and sex-standardized incidence rates were estimated. RESULTS: A total of 568 new MS cases were diagnosed in Puerto Rico between 2017 and 2020. The 2020 MS cumulative prevalence for Puerto Rico was 95.3/100,000 (95% CI: 91.6, 99.1), higher than previously reported. The age- and sex-standardized MS incidence rate for Puerto Rico decreased from 6.5/100,000 (2017) to 6.3/100,000 (2020). The annual age-standardized MS incidence rates declined for females: from 9.5/100,000 (2017) to 8.2/100,000 (2020) but increased for males from 3.6/100,000 to 4.6/100,000 during the same period. CONCLUSION: These incidence and prevalence rates are among the highest reported among Caribbean and Latin American countries. A peak in the age- and sex-standardized MS incidence rate was observed after hurricane María (2018) and a decline during the first year of the COVID-19 pandemic (2020). Further investigation is needed to determine whether there was a causal relationship between the fluctuations observed and those natural events.

The Role of Associative Learning in Current Paradigm Shifts in Eating Disorder Research and Clinical Practice.

This editorial is an introduction to the Special Issue "Psychopathological analysis and intervention for anorexia nervosa: using associative-learning mechanisms" [...].

Evaluation of the robustness of cerebral oximetry to variations in skin pigmentation using a tissue-simulating phantom.

Clinical studies have demonstrated that epidermal pigmentation level can affect cerebral oximetry measurements. To evaluate the robustness of these devices, we have developed a phantom-based test method that includes an epidermis-simulating layer with several melanin concentrations and a 3D-printed cerebrovascular module. Measurements were performed with neonatal, pediatric and adult sensors from two commercial oximeters, where neonatal probes had shorter source-detector separation distances. Referenced blood oxygenation levels ranged from 30 to 90%. Cerebral oximeter outputs exhibited a consistent decrease in saturation level with simulated melanin content; this effect was greatest at low saturation levels, producing a change of up to 15%. Dependence on pigmentation was strongest in a neonatal sensor, possibly due to its high reflectivity. Overall, our findings indicate that a modular channel-array phantom approach can provide a practical tool for assessing the impact of skin pigmentation on cerebral oximeter performance and that modifications to algorithms and/or instrumentation may be needed to mitigate pigmentation bias.

Implicit and explicit measures of the sensory and hedonic analysis of beer: The role of tasting expertise.

Measures of drinking and eating behaviors may be assessed both explicitly (e.g., sensory and quality judgments) and implicitly (e.g., Electroencephalography, EEG), although the relationship between the results of both approaches remains unclear and each might be differentially affected by acquired knowledge. The main aim of the present study was to determine the strength of the relationship between these measures in sensory and hedonic processing of beers depending on the degree of tasting expertise. Beer experts, experts in non-beer beverages or edibles, and non-expert consumers took part in a sensory analysis procedure where they rated beers in terms of their sensory attributes and general quality-visual, olfactory, and gustatory phases-as well as their global hedonic value while their brain activity was recorded. The results suggest that participants evaluated the sensory properties of the beers in a rather similar manner. However, during the gustatory phase, experts and general tasters differed in terms of the activation of brain areas related to memory processes, while general tasters and consumers differed in brain activation related to hedonic processing. The relationship between self-reported quality judgments and EEG activity - particularly in relation to recognition and working memory components - appeared to be stronger in experts in comparison with the other groups (lowest |r| = 0.67, p < .01). Although lower in number, significant relationships were also found in general tasters and consumers, primarily involving hedonic processing (lowest |r| = 0.58, p < .01) and recognition memory (lowest |r| = 0.57, p < .01) components. Moreover, those relationships differed significantly, mostly between experts and consumers (lowest |z| = 2.68, p < .01), in terms of the involvement of working memory components. Taken together, the results of this study suggest that beer experts have a more efficient pattern of gustatory processing and show a better fit between explicit (judgments) and implicit (EEG) measures of sensory and hedonic quality of beers.

Stimulus Reward Value Interacts with Training-induced Plasticity in Inhibitory Control.

Training inhibitory control, the ability to suppress motor or cognitive processes, not only enhances inhibition processes, but also reduces the perceived value and behaviors toward the stimuli associated with the inhibition goals during the practice. While these findings suggest that inhibitory control training interacts with the aversive and reward systems, the underlying spatio-temporal brain mechanisms remain unclear. We used electrical neuroimaging analyses of event-related potentials to examine the plastic brain modulations induced by training healthy participants to inhibit their responses to rewarding (pleasant chocolate) versus aversive food pictures (unpleasant vegetables) with Go/NoGo tasks. Behaviorally, the training resulted in a larger improvement in the aversive than in the rewarding NoGo stimuli condition, suggesting that reward responses impede inhibitory control learning. The electrophysiological results also revealed an interaction between reward responses and inhibitory control plasticity: we observed different effects of practice on the rewarding vs. aversive NoGo stimuli at 200 ms post-stimulus onset, when the conflicts between automatic response tendency and task demands for response inhibition are processed. Electrical source analyses revealed that this effect was driven by an increase in right orbito-cingulate and a decrease in temporo-parietal activity to the rewarding NoGo stimuli and the reverse pattern to the aversive stimuli. Our collective results provide direct neurophysiological evidence for interactions between stimulus reward value and executive control training, and suggest that changes in the assessment of stimuli with repeated motoric inhibition likely follow from associative learning and behavior-stimulus conflicts reduction mechanisms.

Age-Adapted Stress Task in Preschoolers Does not Lead to Uniform Stress Responses.

Acute stress response measures serve as an indicator of physiological functioning, but have previously led to contradictory results in young children due to age-related cortisol hypo-responsivity and methodological inconsistencies in assessment. The aim of this study was to investigate stress responses during a validated age-adapted socio-evaluative stress task in children aged 2-6 years in a child care environment and to detect socio-demographic, task- and child-related characteristics of stress responses. Stress responses were assessed in 323 children for salivary cortisol and salivary alpha amylase (sAA), and in 328 children for changes in heart rate variability (HRV). These data were then associated with socio-demographic (e.g. SES), task-related (e.g. task length) and child-related characteristics (e.g. self-regulation) of stress responses using multilevel models. Analyses revealed elevated sympathetic reactivity (sAA: Coeff=0.053, p=0.004) and reduced HRV (Coeff=-0.465, p<0.001), but no hypothalamic-pituitary-adrenal (HPA) response (Coeff=0.017, p=0.08) during the stress task. Child's age (Coeff=-5.82, p<0.001) and movement during the task (Coeff=-0.17, p=0.015) were associated with acute cortisol release, while diurnal sAA was associated with acute sAA release (Coeff=0.24, p<0.001). Age (Coeff=-0.15, p=0.006) and duration of the task (Coeff=0.13, p=0.015) were further associated with change of HRV under acute stress condition. Children showed inconsistent stress responses which contradicts the assumption of a parallel activation of both stress systems in a valid stress task for young children and might be explained by a pre-arousal to the task of young children in a child care setting. Further results confirm that child- and task-related conditions need to be considered when assessing stress responses in these young children.

Effects of familiarization on odor hedonic responses and food choices in children with autism spectrum disorders.

This study assessed whether olfactory familiarization can render food odors more pleasant, and consequently food more attractive, to children with autism spectrum disorder. Participants were first presented with a series of food odors (session 1). Then, they were familiarized on four occasions (time window: 5 weeks) with one of the two most neutral odors (the other neutral odor was used as control) (session 2). In session 3, participants smelled the entire series of odors again. Both verbal and facial responses were compared from session 1 to session 3. After session 3, the children were presented with two identical foods (one containing the familiarized odor and one the control odor) and were asked to choose between these foods. Results revealed (1) a specific increase in positive emotions for the familiarized odor and (2) that 68% of the children chose the food associated with the "familiarized odor" (children who chose the "familiarized odor" food exhibited significantly more sensory particularities). These findings suggest that it is possible to modulate olfactory emotions and expand the dietary repertoire of children with autism spectrum disorder. Application of this paradigm may enable innovative prospects for food education in autism.

Self-reported emotion regulation difficulties are associated with mood but not with the biological stress response to thin ideal exposure.

BACKGROUND: Difficulties in emotion regulation have been related to psychological and physiological stress responses such as lower mood and lower parasympathetic activation (HF-HRV) under resting condition, but evidence on the potential link to the hypothalamic-pituitary-adrenal (HPA) axis functioning and to physiological stress responses during a stress task is still scarce. The aim of the study was to investigate stress responses in young women when confronted to a daily stressor such as exposure to thin ideals and to understand the role of correlates of self-reported trait-like emotion regulation difficulties (ERD). METHODS: Heart rate variability (HRV) and salivary cortisol data were collected in a sample of 273 young women aged 18-35 with and without mental disorders during a vivid imagination of thin ideals (experimental condition) or landscapes (control condition). Changes in mood states were measured on a visual analogue scale (0-100). Correlates of trait-like ERD were self-reported using the Difficulties in Emotion Regulation Scale (DERS). RESULTS: Participants with higher ERD showed a stronger decline in self-reported mood after vivid imagination of thin ideals compared to participants with lower ERD in the experimental condition but also a stronger increase of positive mood with increasing ERD in the control condition. ERD were not related to baseline HF-HRV or baseline salivary cortisol levels nor to any physiological response during and after the imagination of thin ideals. DISCUSSION AND CONCLUSION: The results corroborate the role of ERD regarding the immediate psychological impact of daily stressors. Exposition to daily stressors in the laboratory results in discrepant psychological and physiological reactivity. Future studies should investigate under what conditions the complex interrelations between immediate and long-term ERD and biological activation are amenable to assessment in a laboratory setting. The additive effects of multiple exposition to stressors, such as thin ideals in daily life, also need to be addressed.

How Does Food Taste in Anorexia and Bulimia Nervosa? A Protocol for a Quasi-Experimental, Cross-Sectional Design to Investigate Taste Aversion or Increased Hedonic Valence of Food in Eating Disorders.

Background: Despite on-going efforts to better understand dysregulated eating, the olfactory-gustatory deficits and food preferences in eating disorders (ED), and the mechanisms underlying the perception of and responses to food properties in anorexia nervosa (AN) and bulimia nervosa (BN) remain largely unknown; both during the course of the illness and compared to healthy populations. It is, therefore, necessary to systematically investigate the gustatory perception and hedonics of taste in patients with AN and BN. To this end, we will examine whether aversions to the taste of high-calorie food is related to the suppression of energy intake in restricting-type AN, and whether an increased hedonic valence of sweet, caloric-dense foods may be part of the mechanisms triggering binge-eating episodes in BN. In addition, the role of cognitions influencing these mechanisms will be examined. Method: In study 1, four mixtures of sweet-fat stimuli will be presented in a sensory two-alternative forced-choice test involving signal detection analysis. In study 2, a full-scale taste reactivity test will be carried out, including psychophysiological and behavioral measures to assess subtle and covert hedonic changes. We will compare the responses of currently-ill AN and BN patients to those who have recovered from AN and BN, and also to those of healthy normal-weight and underweight individuals without any eating disorder pathology. Discussion: If taste response profiles are differentially linked to ED types, then future studies should investigate whether taste responsiveness represents a useful diagnostic measure in the prevention, assessment and treatment of EDs. The expected results on cognitive mechanisms in the top-down processes of food hedonics will complement current models and contribute to the refinement of interventions to change cognitive aspects of taste aversions, to establish functional food preferences and to better manage food cravings associated with binge-eating episodes. No trial registration was required for this protocol, which was approved by the Swiss ethics committee (CER-VD, n° 2016-02150) and the Ethics Review Panel of the University of Luxembourg.

Emotional eating is related with temperament but not with stress biomarkers in preschool children.

Emotional eating (EE) corresponds to a change in eating behavior in response to distress and results in an increase of food intake (overeating (EOE)) or in food avoidance (undereating (EUE)). EE has been related to temperament (i.e. negative emotionality) and dysregulated stress biomarkers in school-aged children; parenting has been understood to influence this relationship in older children. The aim of the study was to investigate to which extent stress biomarkers and negative emotionality are related to EE and to understand the role of parenting in this relationship. The sample consisted of 271 children aged 2-6 years of the Swiss cohort study SPLASHY. We assessed the child's EE, negative emotionality and parenting by parent based reports. Salivary samples were collected over two days to analyze cortisol and salivary alpha-amylase levels. From the whole sample of children, 1.1% showed EOE and 32.9% EUE. Negative emotionality was related to EOE and EUE (0.13 (CI 0.06, 021), p < 0.001; 0.25 (CI 0.14, 0.35), p < 0.001). There was no relationship between stress biomarkers and EE and parenting had any moderating role (all p > 0.05). Similar to a Danish study, parents reported more often EUE than EOE of their child. Both are related to the temperament. Even though the course of EE has not yet been well documented, we conclude that a certain subgroup of children with difficult temperament could be at-risk for eat and weight regulation problems in later childhood.

Visual attention to food cues is differentially modulated by gustatory-hedonic and post-ingestive attributes.

Although attentional biases towards food cues may play a critical role in food choices and eating behaviours, it remains largely unexplored which specific food attribute governs visual attentional deployment. The allocation of visual attention might be modulated by anticipatory postingestive consequences, from taste sensations derived from eating itself, or both. Therefore, in order to obtain a comprehensive understanding of the attentional mechanisms involved in the processing of food-related cues, we recorded the eye movements to five categories of well-standardised pictures: neutral non-food, high-calorie, good taste, distaste and dangerous food. In particular, forty-four healthy adults of both sexes were assessed with an antisaccade paradigm (which requires the generation of a voluntary saccade and the suppression of a reflex one) and a free viewing paradigm (which implies the free visual exploration of two images). The results showed that observers directed their initial fixations more often and faster on items with high survival relevance such as nutrient and possible dangers; although an increase in antisaccade error rates was only detected for high-calorie items. We also found longer prosaccade fixation duration and initial fixation duration bias score related to maintained attention towards high-calorie, good taste and danger categories; while shorter reaction times to correct an incorrect prosaccade related to less difficulties in inhibiting distasteful images. Altogether, these findings suggest that visual attention is differentially modulated by both the accepted and rejected food attributes, but also that normal-weight, non-eating disordered individuals exhibit enhanced approach to food's postingestive effects and avoidance of distasteful items (such as bitter vegetables or pungent products).

Disentangling the Effect of Valence and Arousal on Judgments Concerning Moral Transgressions.

An increasing body of research has investigated the effect of emotions on judgments concerning moral transgressions. Yet, few studies have controlled for arousal levels associated with the emotions. High arousal may affect moral processing by triggering attention to salient features of transgressions, independently of valence. Therefore previously documented differences in effects of negative and positive emotions may have been confounded by differences in arousal. We conducted two studies to shed light on this issue. In Study 1 we developed a questionnaire including vignettes selected on the basis of psychometrical properties (i.e., mean ratings of the actions and variability). This questionnaire was administered to participants in Study 2, after presenting them with selected pictures inducing different valence but equivalent levels of arousal. Negative pictures led to more severe moral judgments than neutral (p = .054, d = 0.60) and positive pictures (p = .002, d = 1.02), for vignettes that were not associated with extreme judgments. In contrast, positive pictures did not reliably affect judgments concerning such vignettes. These findings suggest that the observed effects of emotions cannot be accounted for by an increase in attention linked to the arousal which accompanies these emotions.

Is sensory-specific satiety for a bitter-sweet infusion modulated by context?

The sensory-affective attributes of beverages have an important influence on a given intake and successive consumptions because of sensory-specific satiety (SSS; defined as a decrease in pleasantness ratings of a food eaten relative to uneaten foods). No studies have, however, investigated how multiple sessions of SSS for familiar drinks over a period of several days up to a week may change their pleasantness and how these hedonic-related judgments are affected by the context during SSS testing. With twenty-six participants, the present study explored the medium lasting and contextual effects of repeated SSS sessions for a bitter-sweet infusion on olfactory and flavour pleasantness over the course of three exposures in either a laboratory or a cafeteria setting. The results showed olfactory and flavour SSS for the infusion following each consumption in both the artificial and the natural setting. More interestingly, despite the failure to detect medium-term SSS (i.e., a greater decrease in pleasantness ratings of a food eaten relative to uneaten foods after repeated SSS sessions over several days as compared to the first SSS session), a contextual modulation of olfactory SSS was observed with a lesser overall magnitude in the cafeteria compared to the laboratory setting. To the best of our knowledge, the impact of eating location on the development of satiation and the differential contextual sensitivity of SSS for orthonasal odours and flavours has not been reported previously. The implications of potential environmental control of SSS are considered in this study.

Disentangling the effect of valence and arousal on judgments concerning moral transgressions

An increasing body of research has investigated the effect of emotions on judgments concerning moral transgressions. Yet, few studies have controlled for arousal levels associated with the emotions. High arousal may affect moral processing by triggering attention to salient features of transgressions, independently of valence. Therefore previously documented differences in effects of negative and positive emotions may have been confounded by differences in arousal. We conducted two studies to shed light on this issue. In Study 1 we developed a questionnaire including vignettes selected on the basis of psychometrical properties (i.e., mean ratings of the actions and variability). This questionnaire was administered to participants in Study 2, after presenting them with selected pictures inducing different valence but equivalent levels of arousal. Negative pictures led to more severe moral judgments than neutral (p = .054, d = 0.60) and positive pictures (p = .002, d = 1.02), for vignettes that were not associated with extreme judgments. In contrast, positive pictures did not reliably affect judgments concerning such vignettes. These findings suggest that the observed effects of emotions cannot be accounted for by an increase in attention linked to the arousal which accompanies these emotions (AU)

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Analysis of blocking of flavor-preference conditioning based on nutrients and palatable tastes in rats.

In Experiment 1 rats were given training in which a mixture of two flavors was paired with sucrose. This established a substantial preference for each of the flavors; however, when rats were given prior experience with just one of the flavors paired with sucrose, training with the compound produced only a weak preference for the other - an example of the blocking effect, well known in other associative learning paradigms. Both the palatable taste of sucrose and its nutrient properties contribute to its ability to reinforce preference acquisition. The role of these two forms of learning was examined in two further experiments in which the reinforcer used was fructose (which is considered to support preference learning because it is palatable but not through its nutrient properties) or maltodextrin (thought to support preference learning by way of its nutrient properties). In neither case was blocking observed. At the theoretical level, this outcome constitutes a challenge to the attempt to explain flavor-preference learning in terms of the standard principles of associative learning theory. Its implication at the level of application is that the potential of the blocking procedure as a technique for preventing the development of unwanted flavor preferences may be limited.