How not to think about immediate dietary and postingestional influences on appetites and satieties

The tongue map and the spatial modulation of taste perception

There is undoubtedly a spatial component to our experience of gustatory stimulus qualities such as sweet, bitter, salty, sour, and umami, however its importance is currently unknown. Taste thresholds have been shown to differ at different locations within the oral cavity where gustatory receptors are found. However, the relationship between the stimulation of particular taste receptors and the subjective spatially-localized experience of taste qualities is uncertain. Although the existence of the so-called ‘tongue map’ has long been discredited, the psychophysical evidence clearly demonstrates significant (albeit small) differences in taste sensitivity across the tongue, soft palate, and pharynx (all sites where taste buds have been documented). Biases in the perceived localization of gustatory stimuli have also been reported, often resulting from tactile capture (i.e., a form of crossmodal, or multisensory, interaction). At the same time, varying responses to supratheshold tastants along the tongue's anterior-posterior axis have putatively been linked to the ingestion-ejection response. This narrative review highlights what is currently known concerning the spatial aspects of gustatory perception, considers how such findings might be explained, given the suggested balanced distribution of taste receptors for each basic taste quality where taste papillae are present, and suggests why knowing about such differences may be important.

•

The existence of the tongue map has long been discredited.

•

Taste receptors in the oral cavity respond to all tastes regardless of their location.

•

Human psychophysical data highlights a significant spatial modulation of taste perception in the oral cavity.

•

Highly-controlled studies of taste psychophysics rarely capture the full multisensory experience associated with eating and drinking.

Is comfort food actually comforting for emotional eaters? A (moderated) mediation analysis

An important but unreplicated earlier finding on comfort eating was that the association between food intake and immediate mood improvement appeared to be mediated by the palatability of the food, and that this effect was more pronounced for high than for low emotional eaters [26]. This has not yet been formally tested using mediation and moderated mediation analysis. We conducted these analyses using data from two experiments on non-obese female students (n = 29 and n = 74). Mood and eating satisfaction in Study 1, and mood, tastiness and emotional eating in Study 2 were all self-reported. In Study 1, using a sad mood induction procedure, emotional eaters ate more food, and when mood was assessed immediately after food intake, 'eating satisfaction' acted as mediator between food intake and mood improvement (decrease in sadness or increase in happiness). In Study 2, where we measured the difference in actual food intake after a control or a stress task (modified Trier Social Stress Test), and assessed mood during the food intake after stress, we found significant moderated mediation. As expected, there was a significant positive mediation effect of tastiness between food intake and mood improvement in the high emotional eaters, but also a significant negative mediation effect of tastiness between food intake and mood improvement in the low emotional eaters. This suggests that tastiness promotes 'comfort' from food in female emotional eaters, but conflicts in non-emotional eaters with a tendency to eat less when stressed. In conclusion, palatable food may indeed provide comfort specifically for high emotional eaters during eating.

Learnt reduction in the size of a meal. Measurement of the sensory-gastric inhibition from conditioned satiety

Many experiments on the role of learning in the amount eaten at a distinctive test meal have been claimed to observe "conditioned satiety." None published from outside this author's group has used either the necessary design of the contingencies to be learnt or the measurements that distinguish a sating effect from other loss of interest in food. One experiment has just been published without an adequate design but giving the best evidence yet from another group for the conditioning of sensory-gastric satiety; yet the authors conclude for changes in sensory preference with no learnt gastric involvement in the meal size response. To encourage correct use of the demonstrations in rats, monkeys and people of conditioned satiety and its mechanism, this paper briefly reviews publications that attribute control of meal size to learnt satiety.

Physiological regulation through learnt control of appetites by contingencies among signals from external and internal environments

As reviewed by [Cooper, S. J. (2008). From Claude Bernard to Walter Cannon: emergence of the concept of homeostasis. Appetite 51, 419-27.] Claude Bernard's idea of stabilisation of bodily states, as realised in Walter B. Cannon's conception of homeostasis, took mathematical form during the 1940s in the principle that externally originating disturbance of a physiological parameter can feed an informative signal around the brain to trigger counteractive processes--a corrective mechanism known as negative feedback, in practice reliant on feedforward. Three decades later, enough was known of the physiology and psychology of eating and drinking for calculations to show how experimentally demonstrated mechanisms of feedforward that had been learnt from negative feedback combine to regulate exchanges of water and energy between the body and the surroundings. Subsequent systemic physiology, molecular neuroscience and experimental psychology, however, have been traduced by a misconception that learnt controls of intake are 'non-homeostatic', the myth of biological 'set points' and an historic failure to address evidence for the ingestion-adapting information-processing mechanisms on which an operationally integrative theory of eating and drinking relies.

Liking vs. wanting food: importance for human appetite control and weight regulation

Current train of thought in appetite research is favouring an interest in non-homeostatic or hedonic (reward) mechanisms in relation to overconsumption and energy balance. This tendency is supported by advances in neurobiology that precede the emergence of a new conceptual approach to reward where affect and motivation (liking and wanting) can be seen as the major force in guiding human eating behaviour. In this review, current progress in applying processes of liking and wanting to the study of human appetite are examined by discussing the following issues: How can these concepts be operationalised for use in human research to reflect the neural mechanisms by which they may be influenced? Do liking and wanting operate independently to produce functionally significant changes in behaviour? Can liking and wanting be truly experimentally separated or will an expression of one inevitably contain elements of the other? The review contains a re-examination of selected human appetite research before exploring more recent methodological approaches to the study of liking and wanting in appetite control. In addition, some theoretical developments are described in four diverse models that may enhance current understanding of the role of these processes in guiding ingestive behaviour. Finally, the implications of a dual process modulation of food reward for weight gain and obesity are discussed. The review concludes that processes of liking and wanting are likely to have independent roles in characterising susceptibility to weight gain. Further research into the dissociation of liking and wanting through implicit and explicit levels of processing would help to disclose the relative importance of these components of reward for appetite control and weight regulation.

Perceptual channels for the texture of a food

The present study makes a start on characterising the cognitive processes by which physical effects of eating on the senses are transformed into quantitative judgments about perceived characteristics of a food. It was hypothesised that there is a discrete perceptual channel for an aspect of texture sensed during each of the three initial movements of eating a piece of a cookie. The results showed that the force required for initial compression of the surface of the biscuit related to how 'crisp' it was. Scores on 'hard' were sensitive to higher forces being required to bite off a piece. Ratings of crunchiness responded to both amplitude and frequency of the cracks opened up in this heterogeneously structured material during the first crushing of the bitten piece. These findings are being pursued to identify the stimulation patterns more precisely and to measure how the percepts are integrated into judgments of overall texture.

Seasonal alteration in taste detection and recognition threshold in seasonal affective disorder: the proximate source of carbohydrate craving

Increased appetite with associated carbohydrate craving are core symptoms of seasonal affective disorder (SAD) and have been attributed to decreased central serotonergic function. The proximate mechanisms for centrally mediated selective macronutrient consumption are unknown. We questioned whether seasonal alterations in taste sensation could serve as a mediator of dietary intake, as implied by the term 'craving'. Specifically, individuals who were seasonally depressed and reported carbohydrate craving would be more sensitive to gustatory cues associated with the presence of carbohydrate than nondepressed subjects. Taste detection and recognition thresholds for the four primary gustatory sensations--sweet, sour, salty, and bitter--were obtained in a group of 25 SAD patients and 23 non-psychiatric subjects during the winter, after 2 weeks of 10 000 lux morning and evening light treatment, and during the summer. Relative to the comparison group, the SAD group was less sensitive to sweet taste during the winter. Sweet taste threshold in the SAD group normalized during the summer; however, 2 weeks of light treatment failed to alter sweet detection thresholds in the SAD group. Moreover, within the SAD group, season exerted significant effects on sweet, sour, and bitter detection, but it did not influence salt-detection thresholds. The findings represent the first demonstration of specific changes in taste perception associated with the self-report of carbohydrate craving in SAD and are discussed in terms of the development of sweet craving and the serotonin hypothesis of SAD.

Food reward: brain substrates of wanting and liking

What are the neural substrates of food reward? Are reward and pleasure identical? Can taste pleasure be assessed in animals? Is reward necessarily conscious? These questions have re-emerged in recent years, and there is now sufficient evidence to prompt re-examination of many preconceptions concerning reward and its relation to brain systems. This paper reviews evidence from many sources regarding both the psychological structure of food reward and the neural systems that mediate it. Special attention is paid to recent evidence from "tasty reactivity" studies of affective reactions to food. I argue that this evidence suggests the following surprising possibilities regarding the functional components and brain substrates of food reward. (1) Reward contains distinguishable psychological or functional components--"liking" (pleasure/palatability) and "wanting" (appetite/incentive motivation). These can be manipulated and measured separately. (2) Liking and wanting have separable neural substrates. Mediation of liking related to food reward involves neurotransmitter systems such as opioid and GABA/benzodiazepine systems, and anatomical structures such as ventral pallidum and brainstem primary gustatory relays. Mediation of wanting related to food reward involves mesotelencephalic dopamine systems, and divisions of nucleus accumbens and amygdala. Both liking and wanting arise from vastly distributed neural systems, but the two systems are separable. (3) Neural processing of food reward is not confined to the limbic forebrain. Aspects of food reward begin to be processed in the brainstem. A neural manipulation can enhance reward or produce aversion but no single lesion or transection is likely abolish all properties of food reward. (4) Both wanting and liking can exist without subjective awareness. Conscious experience can distort or blur the underlying reward process that gave rise to it. Subjective reports may contain false assessments of underlying processes, or even fail at all to register important reward processes. The core processes of liking and wanting that constitute reward are distinct from the subjective report or conscious awareness of those processes.

Effects of time of day and appropriateness on food intake and hedonic ratings at morning and midday

In societies such as the U.S.A. many foods are considered appropriate or inappropriate for particular meals. Although some previous work has indicated that hedonic ratings reflect these cultural patterns, little is known about the impact of time of day and "appropriateness" in particular on food acceptance and intake. The purpose of the present study was to explore the role of appropriateness on consumption and hedonic ratings of breakfast and non-breakfast foods. Experiment 1 examined these factors in the context of four meals in which the type of menu (breakfast or lunch) was factorially combined with time of day (breakfast time or lunchtime). Experiment 2 examined hedonic ratings obtained in the morning and afternoon using samples of the same foods and rating methods used in Experiment 1. Experiment 3 replicated Experiment 2 but employed the rating methods used in Birch et al. (1984). Results from the three experiments indicated that the appropriateness or inappropriateness of when foods were served had no effect upon hedonic ratings and no clear impact on food intake. Postmeal hunger ratings in Experiment 1, however, provided some support for the salience of appropriateness. These results suggest that appropriateness may be more relevant to food selection than to consumption or palatability per se.

Some suggestions on dealing with palatability--response to Ramirez

The understanding of the word "palatability" is explained within a research context consisting of four components: an ingestor, an ingestant, a response measure, and an observer. Within this context a solution is proposed to the circularity of an observer measuring palatability by the amount of ingestive activity and in turn attributing the amount ingested to a measure of palatability. The use of measurements under standardized conditions is emphasized and the suggestion is made that palatability be qualified by the operations which affect variability in measurements of its magnitude. For example, "intrinsic" or "food-generated palatability" is defined as the variability in ratings attributable to changes in the sensory properties of ingested items which are intrinsic to the items being tested. "Learned palatability" could be used for changes in the response to a food attributable to pairing of its sensory properties with post-ingestional effects. The way out of the dilemma posed by the question "do palatable foods induce obesity?", is to determine the relative contributions to excessive intake, which can induce obesity, made by the various sorts of palatabilities, designated by the operations which generate their definitions. In the end this process could render the word "palatable" obsolete.