Age differences in the brain mechanisms of good taste

Prevalence and clinical correlates of benzodiazepine use in the patients with major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a serious and disabling condition characterized by abnormal mood changes. Clinical guidelines for depression treatment recommend antidepressant medications, with benzodiazepines acting as short-term synergists. However, little is currently known about the prevalence and associated clinical risk factors of benzodiazepine use among Chinese patients with MDD. This study aimed to explore the prevalence and clinical risk factors associated with benzodiazepine use in this population.

METHODS

A total of 2742 patients with MDD (males/females = 816/1926, aged 14-60 years) participated in this cross-sectional observational study. General information and psychosis assessments were collected online. Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9), anxiety symptoms using the Generalized Anxiety Disorder-7 (GAD-7), and sleep problems and suicidal tendencies using the third and ninth items of the PHQ-9. Multivariable logistic regression analysis models were employed to identify factors associated with benzodiazepine use.

RESULTS

The prevalence of benzodiazepine use among patients with MDD was 42.9 %. Among these patients, 99.6 % used a single benzodiazepine, with oxazepam being the most frequently prescribed. Age, severity of sleep problems, depressive symptoms, and anxiety symptoms were significantly correlated with benzodiazepine use (all P < 0.001).

LIMITATIONS

The cross-sectional design of this study precludes establishing causal relationships.

CONCLUSION

Our findings indicate a high prevalence of benzodiazepine use among Chinese patients with MDD. Factors such as severe depressive symptoms, anxiety symptoms, age, and sleep problems appear to be associated with benzodiazepine use. These results underscore the importance of vigilance regarding benzodiazepine use in patients with MDD.

The effect of multiband sequences on statistical outcome measures in functional magnetic resonance imaging using a gustatory stimulus

Recent technical developments have led to the invention of multiband functional magnetic resonance imaging (fMRI) sequences that allow for faster sampling rates. However, some studies have highlighted problems with these sequences, leading to a decreased temporal signal-to-noise ratio (tSNR). In addition, this temporal noise may interfere with detecting reward-related responses in mesolimbic regions. The blood-oxygen-level-dependent signal utilized in the majority of fMRI measurements is relatively slow. Furthermore, the cerebral response to gustatory stimuli would also be relatively slow. Therefore, given the temporal noise issues with multiband sequences, it is unclear whether multiband sequences are necessary for fMRI studies using gustatory stimuli. We thus conducted an fMRI experiment using a gustatory stimulus to investigate the effects of multiband sequences and increased sampling rates on statistical outcome measures. A single-band sequence with a repetition time (TR) of 2 s of phantom fMRI data and gustatory fMRI data from the gustatory regions exhibited the highest tSNR, although the tSNR of this sequence of gustatory fMRI was not statistically different from tSNR of multiband sequences with a TR of 2 s in any of the selected region of interests. Conventional general linear model analysis of fMRI showed that single-band sequences are more advantageous than multiband sequences for detecting brain responses to gustatory stimuli in the primary gustatory cortex. In addition, a Bayesian data comparison showed that data derived from a single-band sequence with a TR of 2 s was optimal for inferring neuronal connectivity in gustatory processing. Therefore, a conventional single-band sequence with a TR of 2 s is more appropriate for fMRI with gustatory stimuli. Image acquisition sequences should be selected aligned with the study objectives and target brain regions.

Lifestyle risks associated with brain functional connectivity and structure

Some lifestyle factors are related to health and brain function and structure, but the brain systems involved are incompletely understood. A general linear model was used to test the associations of the combined and separate lifestyle risk measures of alcohol use, smoking, diet, amounts of physical activity, leisure activity, and mobile phone use, with brain functional connectivity with the high resolution Human Connectome Project (HCP) atlas in 19,415 participants aged 45-78 from the UK Biobank, with replication with HCP data. Higher combined lifestyle risk scores were associated with lower functional connectivity across the whole brain, but especially of three brain systems. Low physical, and leisure and social, activity were associated with low connectivities of the somatosensory/motor cortical regions and of hippocampal memory-related regions. Low mobile phone use, perhaps indicative of poor social communication channels, was associated with low functional connectivity of brain regions in and related to the superior temporal sulcus that are involved in social behavior and face processing. Smoking was associated with lower functional connectivity of especially frontal regions involved in attention. Lower cortical thickness in some of these regions, and also lower subcortical volume of the hippocampus, amygdala, and globus pallidus, were also associated with the sum of the poor lifestyle scores. This very large scale analysis emphasizes how the lifestyle of humans relates to their brain structure and function, and provides a foundation for understanding the causalities that relate to the differences found here in the brains of different individuals.

The human posterior parietal cortex: effective connectome, and its relation to function

The effective connectivity between 21 regions in the human posterior parietal cortex, and 360 cortical regions was measured in 171 Human Connectome Project (HCP) participants using the HCP atlas, and complemented with functional connectivity and diffusion tractography. Intraparietal areas LIP, VIP, MIP, and AIP have connectivity from early cortical visual regions, and to visuomotor regions such as the frontal eye fields, consistent with functions in eye saccades and tracking. Five superior parietal area 7 regions receive from similar areas and from the intraparietal areas, but also receive somatosensory inputs and connect with premotor areas including area 6, consistent with functions in performing actions to reach for, grasp, and manipulate objects. In the anterior inferior parietal cortex, PFop, PFt, and PFcm are mainly somatosensory, and PF in addition receives visuo-motor and visual object information, and is implicated in multimodal shape and body image representations. In the posterior inferior parietal cortex, PFm and PGs combine visuo-motor, visual object, and reward input and connect with the hippocampal system. PGi in addition provides a route to motion-related superior temporal sulcus regions involved in social interactions. PGp has connectivity with intraparietal regions involved in coordinate transforms and may be involved in idiothetic update of hippocampal visual scene representations.

The orbitofrontal cortex, food reward, body weight and obesity

In primates including humans, the orbitofrontal cortex is the key brain region representing the reward value and subjective pleasantness of the sight, smell, taste and texture of food. At stages of processing before this, in the insular taste cortex and inferior temporal visual cortex, the identity of the food is represented, but not its affective value. In rodents, the whole organisation of reward systems appears to be different, with reward value reflected earlier in processing systems. In primates and humans, the amygdala is overshadowed by the great development of the orbitofrontal cortex. Social and cognitive factors exert a top-down influence on the orbitofrontal cortex, to modulate the reward value of food that is represented in the orbitofrontal cortex. Recent evidence shows that even in the resting state, with no food present as a stimulus, the liking for food, and probably as a consequence of that body mass index, is correlated with the functional connectivity of the orbitofrontal cortex and ventromedial prefrontal cortex. This suggests that individual differences in these orbitofrontal cortex reward systems contribute to individual differences in food pleasantness and obesity. Implications of how these reward systems in the brain operate for understanding, preventing and treating obesity are described.

Much Ado About Missingness: A Demonstration of Full Information Maximum Likelihood Estimation to Address Missingness in Functional Magnetic Resonance Imaging Data

The current paper leveraged a large multi-study functional magnetic resonance imaging (fMRI) dataset (N = 363) and a generated missingness paradigm to demonstrate different approaches for handling missing fMRI data under a variety of conditions. The performance of full information maximum likelihood (FIML) estimation, both with and without auxiliary variables, and listwise deletion were compared under different conditions of generated missing data volumes (i.e., 20, 35, and 50%). FIML generally performed better than listwise deletion in replicating results from the full dataset, but differences were small in the absence of auxiliary variables that correlated strongly with fMRI task data. However, when an auxiliary variable created to correlate r = 0.5 with fMRI task data was included, the performance of the FIML model improved, suggesting the potential value of FIML-based approaches for missing fMRI data when a strong auxiliary variable is available. In addition to primary methodological insights, the current study also makes an important contribution to the literature on neural vulnerability factors for obesity. Specifically, results from the full data model show that greater activation in regions implicated in reward processing (caudate and putamen) in response to tastes of milkshake significantly predicted weight gain over the following year. Implications of both methodological and substantive findings are discussed.

The use of 'artificial saliva' as a neutral control condition in gustatory research: Artificial saliva is not a neutral gustatory stimulus

Distilled water with NaHCO₃ and KCl is a solution often referred to as 'artificial saliva' because its chemical composition mimics human saliva. It is often used as a control stimulus in gustatory research, especially in neuroimaging, owing to the claim that it does not produce a response in primary gustatory cortex Yet evidence that human research volunteers perceive this liquid as affectively neutral is lacking. Unpublished data from our lab suggested that this solution might be perceived as aversive. This study set out to systematically test the parameters influencing taste neutrality. We used two different concentrations of distilled water with NaHCO₃ and KCl, as well as bottled water as a control stimulus. Healthy adults rated all stimuli on two separate scales to rule out an interpretation based on the specifics of a single scale. Our participants rated artificial saliva as aversive on both scales. The bottled water was rated as neutral in valence on both scales, and as significantly less intense in sensation than both concentrations of the artificial saliva. This is the first study to have directly tested the subjective feelings that accompany the ingestion of these oft-used solutions on a trial-by-trial basis. We found that these stimuli, which were previously assumed to be neutral, may not be perceived as such by research participants. Therefore, future gustatory studies should take care when using this solution as a neutral baseline. It is advised that trial-by-trial ratings are collected. Also, depending on the nature of future studies, bottled water may be considered as a preferable neutral baseline.

Rapid Rule-Based Reward Reversal and the Lateral Orbitofrontal Cortex

Humans and other primates can reverse their choice of stimuli in one trial when the rewards delivered by the stimuli change or reverse. Rapidly changing our behavior when the rewards change is important for many types of behavior, including emotional and social behavior. It is shown in a one-trial rule-based Go-NoGo deterministic visual discrimination reversal task to obtain points, that the human right lateral orbitofrontal cortex and adjoining inferior frontal gyrus is activated on reversal trials, when an expected reward is not obtained, and the non-reward allows the human to switch choices based on a rule. This reward reversal goes beyond model-free reinforcement learning. This functionality of the right lateral orbitofrontal cortex shown here in very rapid, one-trial, rule-based changes in human behavior when a reward is not received is related to the emotional and social changes that follow orbitofrontal cortex damage, and to depression in which this non-reward system is oversensitive and over-connected.

The orbitofrontal cortex: reward, emotion and depression

The orbitofrontal cortex in primates including humans is the key brain area in emotion, and in the representation of reward value and in non-reward, that is not obtaining an expected reward. Cortical processing before the orbitofrontal cortex is about the identity of stimuli, i.e. 'what' is present, and not about reward value. There is evidence that this holds for taste, visual, somatosensory and olfactory stimuli. The human medial orbitofrontal cortex represents many different types of reward, and the lateral orbitofrontal cortex represents non-reward and punishment. Not obtaining an expected reward can lead to sadness, and feeling depressed. The concept is advanced that an important brain region in depression is the orbitofrontal cortex, with depression related to over-responsiveness and over-connectedness of the non-reward-related lateral orbitofrontal cortex, and to under-responsiveness and under-connectivity of the reward-related medial orbitofrontal cortex. Evidence from large-scale voxel-level studies and supported by an activation study is described that provides support for this hypothesis. Increased functional connectivity of the lateral orbitofrontal cortex with brain areas that include the precuneus, posterior cingulate cortex and angular gyrus is found in patients with depression and is reduced towards the levels in controls when treated with medication. Decreased functional connectivity of the medial orbitofrontal cortex with medial temporal lobe areas involved in memory is found in patients with depression. Some treatments for depression may act by reducing activity or connectivity of the lateral orbitofrontal cortex. New treatments that increase the activity or connectivity of the medial orbitofrontal cortex may be useful for depression. These concepts, and that of increased activity in non-reward attractor networks, have potential for advancing our understanding and treatment of depression. The focus is on the orbitofrontal cortex in primates including humans, because of differences of operation of the orbitofrontal cortex, and indeed of reward systems, in rodents. Finally, the hypothesis is developed that the orbitofrontal cortex has a special role in emotion and decision-making in part because as a cortical area it can implement attractor networks useful in maintaining reward and emotional states online, and in decision-making.

Asociación entre el sistema de recompensa del cerebro y elección de comida en adultos mayores y de mediana edad

Introducción. Todos los días las personas toman diferentes decisiones relacionadas con su elección de alimentos, lo que a su vez determina sus hábitos alimenticios. El sistema de recompensa del cerebro (SRC) permite asociar ciertas situaciones con una sensación de placer, lo que influye en la posterior elección de alimentos.Objetivo. Describir cómo influye el SRC en el proceso de elección de comida en adultos de mediana edad y en adultos mayores autosuficientes.Materiales y métodos. Se realizó una búsqueda de la literatura en PubMed y SciELO. Se buscaron artículos escritos en inglés y español y publicados entre 1996 y 2018 utilizando los siguientes términos (en ambos idiomas): ”elección de la comida”, “sistema de recompensa”, “nutrición”, “adulto”, “adulto mayor”, “estado nutricional” y “envejecimiento”.Resultados. 50 artículos cumplieron con los criterios de inclusión. Solo 1 estudio estaba escrito en español; 22 fueron realizados en adultos mayores y el resto en adultos entre 20 y 40 años.Conclusiones. Teniendo en cuenta el escaso número de estudios sobre la conducta alimentaria en general, y en particular sobre la elección de comida en adultos mayores y de mediana edad, es necesario realizar más estudios en Latinoamérica sobre los procesos que subyacen al SRC y su relación con la elección de comida, y cómo estos cambian con la edad para predecir posibles conductas alimentarias e implementar intervenciones efectivas, pues una dieta saludable es esencial para un envejecimiento saludable.

The texture and taste of food in the brain

Oral texture is represented in the brain areas that represent taste, including the primary taste cortex, the orbitofrontal cortex, and the amygdala. Some neurons represent viscosity, and their responses correlate with the subjective thickness of a food. Other neurons represent fat in the mouth, and represent it by its texture not by its chemical composition, in that they also respond to paraffin oil and silicone in the mouth. The discovery has been made that these fat-responsive neurons encode the coefficient of sliding friction and not viscosity, and this opens the way for the development of new foods with the pleasant mouth feel of fat and with health-promoting designed nutritional properties. A few other neurons respond to free fatty acids (such as linoleic acid), do not respond to fat in the mouth, and may contribute to some "off" tastes in the mouth. Some other neurons code for astringency. Others neurons respond to other aspects of texture such as the crisp fresh texture of a slice of apple versus the same apple after blending. Different neurons respond to different combinations of these texture properties, oral temperature, taste, and in the orbitofrontal cortex to olfactory and visual properties of food. In the orbitofrontal cortex, the pleasantness and reward value of the food is represented, but the primary taste cortex represents taste and texture independently of value. These discoveries were made in macaques that have similar cortical brain areas for taste and texture processing as humans, and complementary human functional neuroimaging studies are described.

Food Preferences in Cats: Effect of Dietary Composition and Intrinsic Variables on Diet Selection

Simple Summary

Cats tend to retain food preferences across their lifetime, but intrinsic variables could affect their diet choices so as to preserve internal homoeostasis. This work intended to study the feeding behavior of cats in relation to diet composition and some intrinsic variables (sex, age, and body weight) by analyzing data from a 10-year database of two-feeder food preference tests (2007–2017). Diet mineral components (calcium, crude fiber and ashes) affected food preferences negatively. In addition, the influence of body weight and sex manifested as lower food intake in both females and the heaviest cats (relative to bodyweight). However, only body weight affected food preferences, where the heaviest animals presented the higher preferences overall. During the cold season, animals (especially females) displayed higher food intake, whereas hot seasons increased male cat preferences for palatable diets, hence we observed an interaction between sex and climate season. In conclusion, understanding the relationship that both food composition and some intrinsic variables cats have with their diet preference could help in improving the formulation of specific pet food diets, so that these adequately satisfy the physiological and hedonic needs of domestic cats.

Abstract

A ten-year database of food preference tests (n = 1021; period 2007−2017) was used to explore the feeding behavior of domestic cats. Principal component (PC) analysis and linear regression between food nutrients and preferences (for the most preferred diet of each test; Diet A) were performed. Intake and preference for Diet A were analyzed by intrinsic cats’ variables and climate season. The PC1 (calcium (Ca), phosphorus (P), and ash), PC2 (lipids and ether extract) and PC4 (crude fiber; CF) had borderline significance (p < 0.06; β = −1.42, β = −1.56, and β = 2.68, respectively). Ash and CF contents presented negative correlations with food preference (rho = −0.269, p = 0.031; rho = −0.338, p = 0.006, respectively), and Ca had borderline significance and negative correlation with food preference (rho = −0.241, p = 0.054). Body weight and sex influenced the intake of Diet A, being lower for females (β = 11.758; p = 0.014) and heaviest cats (β = −5.490; p < 0.001). However, only body weight affected food preferences, where the heaviest cats had greater preferences for Diet A. Hot season decreased food intake (β = −2,117; p = 0.032), mostly in females (rho = −3.537; p = 0.002). Males had greater preferences for Diet A during hot seasons (β = 10.216; p = 0.023) and females presented similar preferences throughout the year (p = 0.950). Mineral contents, body weight and sex affected food intake and preferences of cats under the influence of climate season, probably explained by adaptive changes in food detection.

Amygdala activation during unconscious visual processing of food

Hedonic or emotional responses to food have important positive and negative effects on human life. Behavioral studies have shown that hedonic responses to food images are elicited rapidly, even in the absence of conscious awareness of food. Although a number of previous neuroimaging studies investigated neural activity during conscious processing of food images, the neural mechanisms underlying unconscious food processing remain unknown. To investigate this issue, we measured neural activity using functional magnetic resonance imaging while participants viewed food and mosaic images presented subliminally and supraliminally. Conjunction analyses revealed that the bilateral amygdala was more strongly activated in response to food images than to mosaic images under both subliminal and supraliminal conditions. Interaction analyses revealed that the broad bilateral posterior regions, peaking at the posterior fusiform gyrus, were particularly active when participants viewed food versus mosaic images under the supraliminal compared with the subliminal condition. Dynamic causal modeling analyses supported the model in which the subcortical visual pathway from the pulvinar to the amygdala was modulated by food under the subliminal condition; in contrast, the model in which both subcortical and cortical (connecting the primary visual cortex, fusiform gyrus, and the amygdala) visual pathways were modulated by food received the most support under the supraliminal condition. These results suggest the possibility that unconscious hedonic responses to food may exert an effect through amygdala activation via the subcortical visual pathway.

Taste and smell processing in the brain

Taste pathways in humans and other primates project from the nucleus of the solitary tract directly to the taste thalamus, and then to the taste insula. The taste cortex in the anterior insula provides separate and combined representations of the taste, temperature, and texture of food in the mouth independently of hunger and thus of reward value and pleasantness. One synapse on, in the orbitofrontal cortex, these sensory inputs are for some neurons combined by associative learning with olfactory inputs received from the pyriform cortex, and visual inputs from the temporal lobe, and these neurons encode food reward value in that they only respond to food when hungry, and in that activations correlate linearly with subjective pleasantness. Cognitive factors, including word-level descriptions, and selective attention to affective value, modulate the representation of the reward value of taste, olfactory and flavor stimuli in the orbitofrontal cortex and a region to which it projects, the anterior cingulate cortex. These food reward representations are important in the control of appetite, and the liking of food. Individual differences in these reward representations may contribute to obesity, and there are age-related differences in these reward representations.

A low-cost open-architecture taste delivery system for gustatory fMRI and BCI experiments

BACKGROUND

Tasting is a complex process involving chemosensory perception and cognitive evaluation. Different experimental designs and solution delivery approaches may in part explain the variability reported in literature. These technical aspects certainly limit the development of taste-related brain computer interface devices.

NEW METHOD

We propose a novel modular, scalable and low-cost device for rapid injection of small volumes of taste solutions during fMRI experiments that gathers the possibility to flexibly increase the number of channels, allowing complex multi-dimensional taste experiments. We provide the full description of the hardware and software architecture and illustrate the application of the working prototype in single-subject event-related fMRI experiments by showing the BOLD responses to basic taste qualities and to five intensities of tastes during the course of perception.

RESULTS

The device is shown to be effective in activating multiple clusters within the gustatory pathway and a precise time-resolved event-related analysis is shown to be possible by the impulsive nature of the induced perception.

COMPARISON WITH EXISTING METHOD(S)

This gustometer represents the first implementation of a low-cost, easily replicable and portable device that is suitable for all kinds of fMRI taste experiments. Its scalability will boost the experimental design of more complex multi-dimensional fMRI studies of the human taste pathway.

CONCLUSIONS

The gustometer represents a valid open-architecture alternative to other available devices and its spread and development may contribute to an increased standardization of experimental designs in human fMRI studies of taste perception and pave the way to the development of novel taste-related BCIs.

Age but no sex effects on subareas of the amygdala

The amygdala, an anatomical composite of several nuclei that have been grouped anatomically and functionally into three major subareas, has been reported to decrease in size with increasing age and to differ in size between male and female brains. However, findings are rather inconsistent across existing studies, possibly reflecting differences in the cohorts examined or the approaches chosen to define and measure the dimensions of the amygdala. Here, we investigated possible effects of age and sex on the amygdala as well as age-by-sex interactions in 100 healthy subjects (50 men/50 women) aged 18-69 years. For this purpose, we enhanced conventional imaging-based information with microscopically defined cytoarchitectonic probabilities to discriminate between different subareas. We observed significant negative correlations between age and all subareas of the amygdala indicating decreases over time, but with subarea-specific trajectories. In addition, we detected a significant quadratic association with age for the left superficial subarea suggesting an accelerating volume loss over time. Such regional information may serve as a frame of reference in future studies, not only for normative samples but also potentially for clinical populations known to present with an atypical atrophy of the amygdala. There were no sex differences and no interactions between sex and age, suggesting that the size of the amygdala is similar in male and female brains (at least when properly accounting for total intracranial volume) and that its age-related decline follows a similar trajectory in both sexes.

Gustatory responses in macaque monkeys revealed with fMRI: Comments on taste, taste preference, and internal state

Studies of the neural mechanisms underlying value-based decision making typically employ food or fluid rewards to motivate subjects to perform cognitive tasks. Rewards are often treated as interchangeable, but it is well known that the specific tastes of foods and fluids and the values associated with their taste sensations influence choices and contribute to overall levels of food consumption. Accordingly, we characterized the gustatory system in three macaque monkeys (Macaca mulatta) and examined whether gustatory responses were modulated by preferences and hydration status. To identify taste-responsive cortex, we delivered small quantities (0.1 ml) of sucrose (sweet), citric acid (sour), or distilled water in random order without any predictive cues while scanning monkeys using event-related fMRI. Neural effects were evaluated by using each session in each monkey as a data point in a second-level analysis. By contrasting BOLD responses to sweet and sour tastes with those from distilled water in a group level analysis, we identified taste responses in primary gustatory cortex area G, an adjacent portion of the anterior insular cortex, and prefrontal cortex area 12o. Choice tests administered outside the scanner revealed that all three monkeys strongly preferred sucrose to citric acid or water. BOLD responses in the ventral striatum, ventral pallidum, and amygdala reflected monkeys' preferences, with greater BOLD responses to sucrose than citric acid. Finally, we examined the influence of hydration level by contrasting BOLD responses to receipt of fluids when monkeys were thirsty and after ad libitum water consumption. BOLD responses in area G and area 12o in the left hemisphere were greater following full hydration. By contrast, BOLD responses in portions of medial frontal cortex were reduced after ad libitum water consumption. These findings highlight brain regions involved in representing taste, taste preference and internal state.

Appetite, Metabolism and Hormonal Regulation in Normal Ageing and Dementia

Feeding and nutrition follow the growth trajectory of the course of life. The profound physiological changes that human body experiences during ageing affect separate aspects of food intake, from tastant perception to satiety. Concurrent morbidities, such as neurodegeneration, as seen in dementia, and metabolic syndrome, may further shape nutritional behaviours, status and adequacy. In an effort to fill the gap between the exhausting basic research and the actual needs of professionals caring for the exponentially expanding ageing population, the current review addresses major factors relevant to appetite and eating disturbances. Does age alter the perception of food modalities? Is food generally still perceived as alluring and delicious with age? Is there an interplay between ageing, cognitive decline, and malnutrition? What tools can we adopt for proper and timely monitoring? Finally, what anatomical and pathophysiological evidence exists to support a hypothesis of central regulation of metabolic perturbations in normal and accelerated cognitive impairment, and how can we benefit from it in health practice?

Neural processing of food and emotional stimuli in adolescent and adult anorexia nervosa patients

Background

A constant preoccupation with food and restrictive eating are main symptoms of anorexia nervosa (AN). Imaging studies revealed aberrant neural activation patterns in brain regions processing hedonic and reward reactions as well as–potentially aversive–emotions. An imbalance between so called “bottom-up” and “top-down” control areas is discussed. The present study is focusing on neural processing of disease-specific food stimuli and emotional stimuli and its developmental course in adolescent and adult AN patients and could offer new insight into differential mechanisms underlying shorter or more chronic disease.

Methods

33 adolescents aged 12–18 years (15 AN patients, 18 control participants) and 32 adult women (16 AN patients, 16 control participants) underwent functional magnetic resonance imaging (fMRI, 3T high-field scanner) while watching pictures of high and low-calorie food and affective stimuli. Afterwards, they rated subjective valence of each picture. FMRI data analysis was performed using a region of interest based approach.

Results

Pictures of high-calorie food items were rated more negatively by AN patients.

Differences in activation between patients and controls were found in “bottom up” and “top down” control areas for food stimuli and in several emotion processing regions for affective stimuli which were more pronounced in adolescents than in adults.

Conclusion

A differential pattern was seen for food stimuli compared to generally emotion eliciting stimuli. Adolescents with AN show reduced processing of affective stimuli and enhanced activation of regions involved in “bottom up” reward processing and “top down” control as well as the insula with regard to food stimuli with a focus on brain regions which underlie changes during adolescent development. In adults less clear and less specific activation differences were present, pointing towards a high impact that regions undergoing maturation might have on AN symptoms.

Learned Value Shapes Responses to Objects in Frontal and Ventral Stream Networks in Macaque Monkeys

We have an incomplete picture of how the brain links object representations to reward value, and how this information is stored and later retrieved. The orbitofrontal cortex (OFC), medial frontal cortex (MFC), and ventrolateral prefrontal cortex (VLPFC), together with the amygdala, are thought to play key roles in these processes. There is an apparent discrepancy, however, regarding frontal areas thought to encode value in macaque monkeys versus humans. To address this issue, we used fMRI in macaque monkeys to localize brain areas encoding recently learned image values. Each week, monkeys learned to associate images of novel objects with a high or low probability of water reward. Areas responding to the value of recently learned reward-predictive images included MFC area 10 m/32, VLPFC area 12, and inferior temporal visual cortex (IT). The amygdala and OFC, each thought to be involved in value encoding, showed little such effect. Instead, these 2 areas primarily responded to visual stimulation and reward receipt, respectively. Strong image value encoding in monkey MFC compared with OFC is surprising, but agrees with results from human imaging studies. Our findings demonstrate the importance of VLPFC, MFC, and IT in representing the values of recently learned visual images.

Sensory Functioning in Older Adults: Relevance for Food Preference

The world's population is aging and older adults represent the fastest growing segment of the consumer market. Changes in sensory, perceptual and cognitive function in this segment of the population have been described psychophysically, however, more is known about the young-old than the old-old or oldest-old. Only now are we exploring the potential for neuroimaging tools to probe the changes in central nervous system function related to taste and smell that are relevant to sensory perception, reward value, anticipation of and consumption of food stimuli. There is real potential for brain imaging to provide a greater understanding of older adults' consumer behavior.

Age-Related Changes in Gustatory, Homeostatic, Reward, and Memory Processing of Sweet Taste in the Metabolic Syndrome: An fMRI Study

Age affects the human taste system at peripheral and central levels. Metabolic syndrome is a constellation of risk factors (e.g., abdominal obesity and hypertension) that co-occur, increase with age, and heighten risk for cardiovascular disease, diabetes, and cognitive decline. Little is known about how age, metabolic syndrome, and hunger state interact to influence how the brain processes information about taste. We investigated brain activation during the hedonic evaluation of a pleasant, nutritive stimulus (sucrose) within regions critical for taste, homeostatic energy regulation, and reward, as a function of the interactions among age, metabolic syndrome, and hunger condition. We scanned young and elderly adults, half with risk factors associated with metabolic syndrome twice: Once fasted overnight and once after a preload. Functional magnetic resonance imaging data indicated significant effects of age as well as interactive effects with metabolic syndrome and hunger condition. Age-related differences in activation were dependent on the hunger state in regions critical for homoeostatic energy regulation and basic as well as higher order sensory processing and integration. The effects of age and metabolic syndrome on activation in the insula, orbital frontal cortex, caudate, and the hypothalamus may have particularly important implications for taste processing, energy regulation, and dietary choices.

Increased Subjective Distaste and Altered Insula Activity to Umami Tastant in Patients with Bulimia Nervosa

The aim of this study was to examine differences in brain neural activation in response to monosodium glutamate (MSG), the representative component of umami, between patients with bulimia nervosa (BN) and healthy women (HW) controls. We analyzed brain activity after ingestion of an MSG solution using functional magnetic resonance imaging (fMRI) in a group of women with BN (n = 18) and a group of HW participants (n = 18). Both groups also provided a subjective assessment of the MSG solution via a numerical rating scale. The BN group subjectively rated the MSG solution lower in pleasantness and liking than the control group, although no difference in subjective intensity was noted. The fMRI results demonstrated greater activation of the right insula in the BN group versus the control group. Compared with the HW controls, the BN patients demonstrated both altered taste perception-related brain activity and more negative hedonic scores in response to MSG stimuli. Different hedonic evaluation, expressed as the relative low pleasing taste of umami tastant and associated with altered insula function, may explain disturbed eating behaviors, including the imbalance in food choices, in BN patients.

Psychological and Neurobiological Correlates of Food Addiction

Food addiction (FA) is loosely defined as hedonic eating behavior involving the consumption of highly palatable foods (ie, foods high in salt, fat, and sugar) in quantities beyond homeostatic energy requirements. FA shares some common symptomology with other pathological eating disorders, such as binge eating. Current theories suggest that FA shares both behavioral similarities and overlapping neural correlates to other substance addictions. Although preliminary, neuroimaging studies in response to food cues and the consumption of highly palatable food in individuals with FA compared to healthy controls have shown differing activation patterns and connectivity in brain reward circuits including regions such as the striatum, amygdala, orbitofrontal cortex, insula, and nucleus accumbens. Additional effects have been noted in the hypothalamus, a brain area responsible for regulating eating behaviors and peripheral satiety networks. FA is highly impacted by impulsivity and mood. Chronic stress can negatively affect hypothalamic-pituitary-adrenal axis functioning, thus influencing eating behavior and increasing desirability of highly palatable foods. Future work will require clearly defining FA as a distinct diagnosis from other eating disorders.

Functions of the anterior insula in taste, autonomic, and related functions

The anterior insula contains the primary taste cortex, in which neurons in primates respond to different combinations providing a distributed representation of different prototypical tastes, oral texture including fat texture, and oral temperature. These taste neurons do not represent food reward value, in that feeding to satiety does not reduce their responses to zero, in contrast to the next stage of processing, the orbitofrontal cortex, where food reward value is represented. Corresponding results are found with fMRI in humans. A more ventral part of the anterior insula is implicated using fMRI in autonomic-visceral functions. 'Salient' stimuli, including rewarding, punishing, non-rewarding, and novel stimuli may activate this viscero-autonomic system, via inputs received from regions that represent these stimuli such as the orbitofrontal and anterior cingulate cortex. More posteriorly in the insula, there is an oral somatosensory region, and posterior to this somatosensory regions that respond to touch to the body. These taste and somatosensory representations in the insula provide representations that are about the external world (touch), are intermediate (oral taste and texture), and are about internal signals related to visceral and autonomic function. This functionality needs to be taken into account when considering activations of the insula found in cognitive tasks.