The neurocognitive bases of human multimodal food perception: sensory integration

Odor-taste convergence in the nucleus of the solitary tract of the awake freely licking rat

Flavor is produced by the integration of taste, olfaction, texture, and temperature, currently thought to occur in the cortex. However, previous work has shown that brainstem taste-related nuclei also respond to multisensory inputs. Here, we test the hypothesis that taste and olfaction interact in the nucleus of the solitary tract (NTS; the first neural relay in the central gustatory pathway) in awake, freely licking rats. Electrophysiological recordings of taste and taste + odor responses were conducted in an experimental chamber following surgical electrode implantation and recovery. Tastants (0.1 m NaCl, 0.1 m sucrose, 0.01 m citric acid, and 0.0001 m quinine) were delivered for five consecutive licks interspersed with five licks of artificial saliva rinse delivered on a VR5 schedule. Odorants were n-amyl acetate (banana), acetic acid (vinegar), octanoic acid (rancid), and phenylethyl alcohol (floral). For each cell, metric space analyses were used to quantify the information conveyed by spike count, by the rate envelope, and by individual spike timing. Results revealed diverse effects of odorants on taste-response magnitude and latency across cells. Importantly, NTS cells were more competent at discriminating taste + odor stimuli versus tastants presented alone for all taste qualities using both rate and temporal coding. The strong interaction of odorants and tastants at the NTS underscores its role as the initial node in the neural circuit that controls food identification and ingestion.

Cross-modal tactile-taste interactions in food evaluations

Detecting the taste components within a flavoured substance relies on exposing chemoreceptors within the mouth to the chemical components of ingested food. In our paper, we show that the evaluation of taste components can also be influenced by the tactile quality of the food. We first discuss how multisensory factors might influence taste, flavour and smell for both typical and atypical (synaesthetic) populations and we then present two empirical studies showing tactile-taste interactions in the general population. We asked a group of non-synaesthetic adults to evaluate the taste components of flavoured food substances, whilst we presented simultaneous cross-sensory visuo-tactile cues within the eating environment. Specifically, we presented foodstuffs between subjects that were otherwise identical but had a rough versus smooth surface, or were served on a rough versus smooth serving-plate. We found no effect of the serving-plate, but we found the rough/smoothness of the foodstuff itself significantly influenced perception: food was rated as significantly more sour if it had a rough (versus smooth) surface. In modifying taste perception via ostensibly unrelated dimensions, we demonstrate that the detection of tastes within flavours may be influenced by higher level cross-sensory cues. Finally, we suggest that the direction of our cross-sensory associations may speak to the types of hedonic mapping found both in normal multisensory integration, and in the unusual condition of synaesthesia.

Coding of odor stimulus features among secondary olfactory structures

Sensory systems must represent stimuli in manners dependent upon a wealth of factors, including stimulus intensity and duration. One way the brain might handle these complex functions is to assign the tasks throughout distributed nodes, each contributing to information processing. We sought to explore this important aspect of sensory network function in the mammalian olfactory system, wherein the intensity and duration of odor exposure are critical contributors to odor perception. This is a quintessential model for exploring processing schemes given the distribution of odor information by olfactory bulb mitral and tufted cells into several anatomically distinct secondary processing stages, including the piriform cortex (PCX) and olfactory tubercle (OT), whose unique contributions to odor coding are unresolved. We explored the coding of PCX and OT neuron responses to odor intensity and duration. We found that both structures similarly partake in representing descending intensities of odors by reduced recruitment and modulation of neurons. Additionally, while neurons in the OT adapt to odor exposure, they display reduced capacity to adapt to either repeated presentations of odor or a single prolonged odor presentation compared with neurons in the PCX. These results provide insights into manners whereby secondary olfactory structures may, at least in some cases, uniquely represent stimulus features.

Odor-taste convergence in the nucleus of the solitary tract of the awake freely licking rat

Flavor is produced by the integration of taste, olfaction, texture, and temperature, currently thought to occur in the cortex. However, previous work has shown that brainstem taste-related nuclei also respond to multisensory inputs. Here, we test the hypothesis that taste and olfaction interact in the nucleus of the solitary tract (NTS; the first neural relay in the central gustatory pathway) in awake, freely licking rats. Electrophysiological recordings of taste and taste + odor responses were conducted in an experimental chamber following surgical electrode implantation and recovery. Tastants (0.1 m NaCl, 0.1 m sucrose, 0.01 m citric acid, and 0.0001 m quinine) were delivered for five consecutive licks interspersed with five licks of artificial saliva rinse delivered on a VR5 schedule. Odorants were n-amyl acetate (banana), acetic acid (vinegar), octanoic acid (rancid), and phenylethyl alcohol (floral). For each cell, metric space analyses were used to quantify the information conveyed by spike count, by the rate envelope, and by individual spike timing. Results revealed diverse effects of odorants on taste-response magnitude and latency across cells. Importantly, NTS cells were more competent at discriminating taste + odor stimuli versus tastants presented alone for all taste qualities using both rate and temporal coding. The strong interaction of odorants and tastants at the NTS underscores its role as the initial node in the neural circuit that controls food identification and ingestion.

Neural correlates of taste perception in congenital blindness

Sight is undoubtedly important for the perception and the assessment of the palatability of tastants. Although many studies have addressed the consequences of visual impairment on food selection, feeding behavior, eating habits and taste perception, nothing is known about the neural correlates of gustation in blindness. In the current study we examined brain responses during gustation using functional magnetic resonance imaging (fMRI). We scanned nine congenitally blind and 14 age- and sex-matched blindfolded sighted control subjects, matched in age, gender and body mass index (BMI), while they made judgments of either the intensity or the (un)pleasantness of different tastes (sweet, bitter) or artificial saliva that were delivered intra-orally. The fMRI data indicated that during gustation, congenitally blind individuals activate less strongly the primary taste cortex (right posterior insula and overlying Rolandic operculum) and the hypothalamus. In sharp contrast with results of multiple other sensory processing studies in congenitally blind subjects, including touch, audition and smell, the occipital cortex was not recruited during taste processing, suggesting the absence of taste-related compensatory crossmodal responses in the occipital cortex. These results underscore our earlier behavioral demonstration that congenitally blind subjects have a lower gustatory sensitivity compared to normal sighted individuals. We hypothesize that due to an underexposure to a variety of tastants, training-induced crossmodal sensory plasticity to gustatory stimulation does not occur in blind subjects.

Direct behavioral and neurophysiological evidence for retronasal olfaction in mice

The neuroscience of flavor perception is hence becoming increasingly important to understand food flavor perception that guides food selection, ingestion and appreciation. We recently provided evidence that rats can use the retronasal mode of olfaction, an essential element of human flavor perception. We showed that in rats, like humans, odors can acquire a taste. We and others also defined how the input of the olfactory bulb (OB) -not functionally imageable in humans- codes retronasal smell in anesthetized rat. The powerful awake transgenic mouse, however, would be a valuable additional model in the study of flavor neuroscience. We used a go/no-go behavioral task to test the mouse's ability to detect and discriminate the retronasal odor amyl acetate. In this paradigm a tasteless aqueous odor solution was licked by water-restricted head-fixed mice from a lick spout. Orthonasal contamination was avoided. The retronasal odor was successfully discriminated by mice against pure distilled water in a concentration-dependent manner. Bulbectomy removed the mice's ability to discriminate the retronasal odor but not tastants. The OB showed robust optical calcium responses to retronasal odorants in these awake mice. These results suggest that mice, like rats, are capable of smelling retronasally. This direct neuro-behavioral evidence establishes the mouse as a useful additional animal model for flavor research.

Computational gene expression modeling identifies salivary biomarker analysis that predict oral feeding readiness in the newborn

OBJECTIVE

To combine mathematical modeling of salivary gene expression microarray data and systems biology annotation with reverse-transcription quantitative polymerase chain reaction amplification to identify (phase I) and validate (phase II) salivary biomarker analysis for the prediction of oral feeding readiness in preterm infants.

STUDY DESIGN

Comparative whole-transcriptome microarray analysis from 12 preterm newborns pre- and postoral feeding success was used for computational modeling and systems biology analysis to identify potential salivary transcripts associated with oral feeding success (phase I). Selected gene expression biomarkers (15 from computational modeling; 6 evidence-based; and 3 reference) were evaluated by reverse-transcription quantitative polymerase chain reaction amplification on 400 salivary samples from successful (n = 200) and unsuccessful (n = 200) oral feeders (phase II). Genes, alone and in combination, were evaluated by a multivariate analysis controlling for sex and postconceptional age (PCA) to determine the probability that newborns achieved successful oral feeding.

RESULTS

Advancing PCA (P < .001) and female sex (P = .05) positively predicted an infant's ability to feed orally. A combination of 5 genes, neuropeptide Y2 receptor (hunger signaling), adneosine-monophosphate-activated protein kinase (energy homeostasis), plexin A1 (olfactory neurogenesis), nephronophthisis 4 (visual behavior), and wingless-type MMTV integration site family, member 3 (facial development), in addition to PCA and sex, demonstrated good accuracy for determining feeding success (area under the receiver operator characteristic curve = 0.78).

CONCLUSIONS

We have identified objective and biologically relevant salivary biomarkers that noninvasively assess a newborn's developing brain, sensory, and facial development as they relate to oral feeding success. Understanding the mechanisms that underlie the development of oral feeding readiness through translational and computational methods may improve clinical decision making while decreasing morbidities and health care costs.

Imaging methodologies and applications for nutrition research: what can functional MRI offer?

Food intake is influenced by a complex regulatory system involving the integration of a wide variety of sensory inputs across multiple brain areas. Over the past decade, advances in neuroimaging using functional MRI (fMRI) have provided valuable insight into these pathways in the human brain. This review provides an outline of the methodology of fMRI, introducing the widely used blood oxygenation level-dependent contrast for fMRI and direct measures of cerebral blood flow using arterial spin labelling. A review of fMRI studies of the brain's response to taste, aroma and oral somatosensation, and how fat is sensed and mapped in the brain in relation to the pleasantness of food, and appetite control is given. The influence of phenotype on individual variability in cortical responses is addressed, and an overview of fMRI studies investigating hormonal influences (e.g. peptide YY, cholecystokinin and ghrelin) on appetite-related brain processes provided. Finally, recent developments in MR technology at ultra-high field (7 T) are introduced, highlighting the advances this can provide for fMRI studies to investigate the neural underpinnings in nutrition research. In conclusion, neuroimaging methods provide valuable insight into the mechanisms of flavour perception and appetite behaviour.

Oral texture influences the neural processing of ortho- and retronasal odors in humans

Eating implies mutual interactions between different senses. In the present work we aimed at studying relations between food texture and food odor, using both psychophysical and imaging techniques. Eighteen right-handed healthy human subjects participated to both behavioral and fMRI sessions. Fresh, sweetened milk and a more thickened version were delivered orally; in addition, a buttery-cream aroma was presented ortho- or retronasally. Stimuli were applied using a gustometer and or an air-dilution olfactometer, both computer-controlled. In each session subjects rated separately odor-, taste- and thickness intensities of the stimuli. The behavioral data show that odors, presented through either retro- or orthonasal path, induce a significant flavor enhancement with respect to the no-odor condition. Brain functional data indicated a significant enhancement of the activation of olfactory eloquent areas in favor of ortho-nasal odor presentation while activations of mechanosensory areas were favored by the retro-nasal odor route. As effect of oral stimuli we found a significant correlation between the texture intensity rating vs. the BOLD signal in the supplementary motor area, known to drive subconsciously primed movement, putatively associated in this case with the tongue movement required with the handling of the stimulus. Moreover, we found inhibition of the signal in different sensory specific areas as an effect of the mutual interaction between stimulus qualities. In conclusion, ortho- and retronasal odors differentially affect the neural processing of the texture of oral stimuli.

Neural correlates of taste perception in congenital olfactory impairment

Olfaction and gustation contribute both to the appreciation of food flavours. Although acquired loss of smell has profound consequences on the pleasure of eating, food habits and body weight, less is known about the impact of congenital olfactory impairment on gustatory processing. Here we examined taste identification accuracy and its neural correlates using functional magnetic resonance imaging (fMRI) in 12 congenitally olfactory impaired individuals and 8 normosmic controls. Results showed that taste identification was worse in congenitally olfactory impaired compared to control subjects. The fMRI results demonstrated that olfactory impaired individuals had reduced activation in medial orbitofrontal cortex (mOFC) relative to normosmic subjects while tasting. In addition, olfactory performance as measured with the Sniffin' Sticks correlated positively with taste-induced blood-oxygen-level dependent (BOLD) signal increases in bilateral mOFC and anterior insula. Our data provide a neurological underpinning for the reduced taste perception in congenitally olfactory impaired individuals.

Smelling directions: olfaction modulates ambiguous visual motion perception

Senses of smells are often accompanied by simultaneous visual sensations. Previous studies have documented enhanced olfactory performance with concurrent presence of congruent color- or shape- related visual cues, and facilitated visual object perception when congruent smells are simultaneously present. These visual object-olfaction interactions suggest the existences of couplings between the olfactory pathway and the visual ventral processing stream. However, it is not known if olfaction can modulate visual motion perception, a function that is related to the visual dorsal stream. We tested this possibility by examining the influence of olfactory cues on the perceptions of ambiguous visual motion signals. We showed that, after introducing an association between motion directions and olfactory cues, olfaction could indeed bias ambiguous visual motion perceptions. Our result that olfaction modulates visual motion processing adds to the current knowledge of cross-modal interactions and implies a possible functional linkage between the olfactory system and the visual dorsal pathway.

Olfactory preference conditioning changes the reward value of reinforced and non-reinforced odors

Olfaction is determinant for the organization of rodent behavior. In a feeding context, rodents must quickly discriminate whether a nutrient can be ingested or whether it represents a potential danger to them. To understand the learning processes that support food choice, aversive olfactory learning and flavor appetitive learning have been extensively studied. In contrast, little is currently known about olfactory appetitive learning and its mechanisms. We designed a new paradigm to study conditioned olfactory preference in rats. After 8 days of exposure to a pair of odors (one paired with sucrose and the other with water), rats developed a strong and stable preference for the odor associated with the sucrose solution. A series of experiments were conducted to further analyze changes in reward value induced by this paradigm for both stimuli. As expected, the reward value of the reinforced odor changed positively. Interestingly, the reward value of the alternative odor decreased. This devaluation had an impact on further odor comparisons that the animal had to make. This result suggests that appetitive conditioning involving a comparison between two odors not only leads to a change in the reward value of the reinforced odor, but also induces a stable devaluation of the non-reinforced stimulus.

New centrally acting agents for appetite control: from biological mechanisms to clinical efficacy

BACKGROUND

Obesity is one of the major problems of health policy in different countries. Pharmacological attempts have been made to help affected people without a definitive solution. Some agents--either with peripheral or central effect--are available in the market. On July 2012, the FDA approved two novel preparations for obese patients: (1) topiramate-phentermine--the first one an anticonvulsant and the second one a sympathomimetic amine--and (2) lorcaserin, a 5-HT2CR agonist. Both preparations emerged as new options for weight management.

SCOPE

Based on the complex biology of eating behavior, in this review we discuss the features, mechanisms of action, pharmacokinetics, advantages and possible disadvantages of these new agents.

CONCLUSION

With differences in efficacy (higher for the topiramate-phentermine combination), both preparations are active in reducing appetite and body weight, as well as in improving comorbidities. Additional information will be collected from Phase IV surveillance. Focus on cardiovascular, neuropsychiatric (for both introductions) and embrio-fetal safety (especially for topiramate) is expected.

Characterization of the key aroma compounds in pork soup stock by using an aroma extract dilution analysis

The aroma extract dilution analysis of an extract prepared from pork stock and subsequent experiments led to the identification of 15 aroma-active compounds in the flavor dilution factor range of 64-2048. Omission experiments to select the most aroma-active compounds from the 15 odor compounds suggested acetol, octanoic acid, δ-decalactone, and decanoic acid as the main active compounds contributing to the aroma of pork stock. Aroma recombination, addition, and omission experiments of these four aroma compounds in taste-reconstituted pork stock showed that each compound had an individual aroma profile. A comparison of the overall aroma between this recombined mixture and pork stock showed strong similarity, suggesting that the key aroma compounds had been successfully identified.

Where is the comfort in comfort foods? Mechanisms linking fat signaling, reward, and emotion

BACKGROUND

Food in general, and fatty foods in particular, have obtained intrinsic reward value throughout evolution. This reward value results from an interaction between exteroceptive signals from different sensory modalities, interoceptive hunger/satiety signals from the gastrointestinal tract to the brain, as well as ongoing affective and cognitive processes. Further evidence linking food to emotions stems from folk psychology ('comfort foods') and epidemiological studies demonstrating high comorbidity rates between disorders of food intake, including obesity, and mood disorders such as depression.

PURPOSE

This review paper aims to give an overview of current knowledge on the neurophysiological mechanisms underlying the link between (fatty) foods, their reward value, and emotional responses to (anticipation of) their intake in humans. Firstly, the influence of exteroceptive sensory signals, including visual, olfactory ('anticipatory food reward'), and gustatory ('consummatory food reward'), on the encoding of reward value in the (ventral) striatum and of subjective pleasantness in the cingulate and orbitofrontal cortex will be discussed. Differences in these pathways and mechanisms between lean and obese subjects will be highlighted. Secondly, recent studies elucidating the mechanisms of purely interoceptive fatty acid-induced signaling from the gastrointestinal tract to the brain, including the role of gut peptides, will be presented. These studies have demonstrated that such subliminal interoceptive stimuli may impact on hedonic circuits in the brain, and thereby influence the subjective and neural responses to negative emotion induction. This suggests that the effect of foods on mood may even occur independently from their exteroceptive sensory properties.

Studying the effects of smell and taste experience in the pediatric population using functional near infrared spectroscopy: a hypothesis

There are different postnatal sensitive periods throughout the development course of sensory functions. During sensitive periods, there is a biological display of an extreme neural sensitivity to the storage of experience-driven sensory information that is not present outside these developmental stages. This neural property is reflected in subjects' reported preferences for sensory stimuli, such as odors and tastes. The human brain mapping approach (HBA) has demonstrated that disease-free human postnatal and later development of any sensory function parallels morphological and functional development of the CNS and that this development correlates with signal changes that have been acquired by means of neuroimaging techniques. Whether experience with tastes and/or odors has a stronger effect on the perception of gustatory and/or olfactory stimuli the earlier subjects are exposed to certain odors and tastes is still unknown. It is also unknown, whether as well as how this effect is reflected in brain activation patterns and whether we are currently able to identify sensitive periods of gustatory and olfactory development from the imaging signals. To answer these research questions, repeated exposure to tastes and/or odors should be applied in children of different age ranges in order to induce different age-related degrees of olfactory/gustatory preferences as well as different aged-related patterns of oxyhemoglobin (OH) and deoxyhemoglobin (DOH) changes that should be measured by means of the functional near-infrared spectroscopy (fNIRS) technique.

Training, hypnosis, and drugs: artificial synaesthesia, or artificial paradises?

The last few years have seen the publication of a number of studies by researchers claiming to have induced "synaesthesia," "pseudo-synaesthesia," or "synaesthesia-like" phenomena in non-synaesthetic participants. Although the intention of these studies has been to try and shed light on the way in which synaesthesia might have been acquired in developmental synaesthestes, we argue that they may only have documented a phenomenon that has elsewhere been accounted for in terms of the acquisition of sensory associations and is not evidently linked to synaesthesia. As synaesthesia remains largely defined in terms of the involuntary elicitation of conscious concurrents, we suggest that the theoretical rapprochement with synaesthesia (in any of its guises) is unnecessary, and potentially distracting. It might therefore, be less confusing if researchers were to avoid referring to synaesthesia when characterizing cases that lack robust evidence of a conscious manifestation. Even in the case of those other conditions for which conscious experiences are better evidenced, when training has been occurred during hypnotic suggestion, or when it has been combined with drugs, we argue that not every conscious manifestation should necessarily be counted as synaesthetic. Finally, we stress that cases of associative learning are unlikely to shed light on two highly specific characteristic of the majority of cases of developmental synaesthesia in terms of learning patterns: First, their resistance to change through exposure once the synaesthetic repertoire has been fixed; Second, the transfer of conditioned responses between concurrents and inducers after training. We conclude by questioning whether, in adulthood, it is ever possible to acquire the kind of synaesthesia that is typically documented in the developmental form of the condition. The available evidence instead seems to point to there being a critical period for the development of synaesthesia, probably only in those with a genetic predisposition to develop the condition.

The representation of oral fat texture in the human somatosensory cortex

How fat is sensed in the mouth and represented in the brain is important in relation to the pleasantness of food, appetite control, and the design of foods that reproduce the mouthfeel of fat yet have low energy content. We show that the human somatosensory cortex (SSC) is involved in oral fat processing via functional coupling to the orbitofrontal cortex (OFC), where the pleasantness of fat texture is represented. Using functional MRI, we found that activity in SSC was more strongly correlated with the OFC during the consumption of a high fat food with a pleasant (vanilla) flavor compared to a low fat food with the same flavor. This effect was not found in control analyses using high fat foods with a less pleasant flavor or pleasant-flavored low fat foods. SSC activity correlated with subjective ratings of fattiness, but not of texture pleasantness or flavor pleasantness, indicating a representation that is not involved in hedonic processing per se. Across subjects, the magnitude of OFC-SSC coupling explained inter-individual variation in texture pleasantness evaluations. These findings extend known SSC functions to a specific role in the processing of pleasant-flavored oral fat, and identify a neural mechanism potentially important in appetite, overeating, and obesity.

Sensory neuroscience: taste responses in primary olfactory cortex

A new electrophysiological study in rodents demonstrates that taste-odor convergence occurs in posterior piriform olfactory cortex and calls for a reformulation of classic models of the central representation of flavor.

Functional organization of neuronal and humoral signals regulating feeding behavior

Energy homeostasis--ensuring that energy availability matches energy requirements--is essential for survival. One way that energy balance is achieved is through coordinated action of neural and neuroendocrine feeding circuits, which promote energy intake when energy supply is limited. Feeding behavior engages multiple somatic and visceral tissues distributed throughout the body--contraction of skeletal and smooth muscles in the head and along the upper digestive tract required to consume and digest food, as well as stimulation of endocrine and exocrine secretions from a wide range of organs. Accordingly, neurons that contribute to feeding behaviors are localized to central, peripheral, and enteric nervous systems. To promote energy balance, feeding circuits must be able to identify and respond to energy requirements, as well as the amount of energy available from internal and external sources, and then direct appropriate coordinated responses throughout the body.

Localization of the primary taste cortex by contrasting passive and attentive conditions

The primary taste cortex is located in the insula. However, exactly where in the insula the human primary taste cortex is located remains a controversial issue. Human neuroimaging studies have shown prominent variation concerning the location of taste-responsive activation within the insula. A standard protocol for gustatory testing in neuroimaging studies has not been developed, which might underlie such variations. In order to localize the primary taste cortex in an fMRI experiment, we used a taste delivery system to suppress non-taste stimuli and psychological effects. Then, we compared brain response to taste solution during a passive tasting task condition and a taste quality identification task condition to verify whether this cognitive task affected the location of taste-responsive activation within the insula. To examine which part of insula is the primary taste area, we performed dynamic causal modeling (DCM) to verify the neural network of the taste coding-related region and random-effects Bayesian model selection (BMS) at the family level to reveal the optimal input region. Passive tasting resulted in activation of the right middle insula (MI), and the most favorable model selected by DCM analysis showed that taste effect directly influenced the MI. Additionally, BMS results at the family level suggested that the taste inputs entered into the MI. Taken together, our results suggest that the human primary taste cortex is located in the MI.

Evaluation of multisensory stimuli--dimensions of meaning and electrical brain activity

The semantic differential technique is used to statistically define connotative dimensions of meaning. The brain depends on these dimensions to process words. Earlier studies demonstrated that stimuli of the different semantic classes led to differences in neuronal processing. We investigated the influence of connotative meaning on multisensory processing (food words strongly related to odor, taste, vision or somatosensory texture). A group of 795 subjects rated 197 food words on the basis of 11 pairs of adjectives with opposite meanings. Factor analysis revealed three dimensions (Evaluation, Potency and Texture). Words with high positive or negative scores, and low scores on the other dimensions, were used as stimuli in an ERP experiment. EEG was recorded in 40 healthy adults from 30 channels and averaged according to semantic stimulus class. Component latency, global field power and topography were influenced by semantic meaning. These experiments determined that very early effects at 107 ms after stimulus presentation where latency and GFP were affected by stimulus class. When mapped topographically, different stimulus classes led to different scalp topography of evoked brain activity in sagittal direction already at an early state of processing (around 107 ms). The extent of lateralization of potential fields' centers of gravity was influenced by stimulus class around 304 ms. In summary, semantic dimensions influence neuronal processing of words related to multisensory perception. Such effects suggest a rapid and complex way of processing multisensory stimuli.

Children's reward responses to picture- and odor-cued food stimuli: a developmental analysis between 6 and 11years

The reward system is largely involved in the control of food intake. Whether components of this system (i.e., wanting and liking) change during development remains understudied, as well as how proximate factors (sensory cues, motivational state) modulate reward reactivity across development. We examined the developmental pattern of wanting and liking for sensorily-cued food stimuli in 6-11year old children as a function of the child's motivational state (hunger/satiety), gender, and the nature of foods. School children were exposed before or after their lunch on alternative days to visual and odor stimuli representing different categories of familiar foods. Their task was to rate wanting and liking of pictures and odorants of pizza, meat, vegetables, fruits, and chocolate. The following results were found: (1) While liking appeared to be stable from age 6 to 11, more particularly for visually-cued foods, wanting decreased, as well as did subjective hunger perception; (2) there were smaller or absent state-effects in 7-to-9-year-olds; (3) reward ratings were higher in boys than in girls; (4) reward ratings of vegetables were the lowest at all ages. These results suggest that wanting, but not liking, is developmentally variable over childhood, and that this variation depends on age, gender, motivational state (hunger/satiety), the nature of the food and the modality of the sensory cue representing it. Such developmental changes are discussed in relation to biological (adiposity rebound) and cognitive (dietary restraint) factors influencing the motivation to eat during middle (6-7years) and late (9-11years) childhood.

Chemosensory convergence on primary olfactory cortex

Food perception and preference formation relies on the ability to combine information from both the taste and olfactory systems. Accordingly, psychophysical investigations in humans and behavioral work in animals has shown that the taste system plays an integral role in odor processing. However, the neural basis for the influence of taste (gustation) on odor (olfaction) remains essentially unknown. Here we tested the hypothesis that gustatory influence on olfactory processing occurs at the level of primary olfactory cortex. We recorded activity from single neurons in posterior olfactory (piriform) cortex (pPC) of awake rats while presenting basic taste solutions directly to the tongue. A significant portion of pPC neurons proved to respond selectively to taste stimuli. These taste responses were significantly reduced by blockade of the gustatory epithelium, were unaffected by blockade of the olfactory epithelium, and were independent of respiration behavior. In contrast, responses to olfactory stimuli, recorded from the same area, were reduced by nasal epithelial deciliation and phase-locked to the respiration cycle. These results identify pPC as a likely site for gustatory influences on olfactory processing, which play an important role in food perception and preference formation.

Sensory processing issues in young children presenting to an outpatient feeding clinic

OBJECTIVES

The aim of the study was to describe the relation between sensory issues and medical complexity in a series of patients presenting to an outpatient multidisciplinary feeding team for evaluation, by a standardized measure of sensory-processing abilities.

METHODS

A retrospective chart review of all of the patients seen from 2004 to 2009 on 2 key variables: medical diagnostic category and short sensory profile (SSP) score.

RESULTS

On the SSP, 67.6% of children scored in the clinical ("definite difference") range. The most common diagnostic categories were developmental (n = 23), gastrointestinal (n = 16), and neurological (n = 13). Behavioral and cardiorespiratory medical diagnostic categories were significantly related to SSP total score and SSP definite difference score.

CONCLUSIONS

Children who present for feeding evaluation do indeed tend to have clinically elevated scores regarding sensory processing, and these elevated scores are significantly related to certain medical diagnostic categories. Future research is needed to determine why these significant relations exist as well as their implications for treatment of feeding-related issues.

Brain imaging in the context of food perception and eating

PURPOSE OF REVIEW

Eating behavior depends heavily on brain function. In recent years, brain imaging has proved to be a powerful tool to elucidate brain function and brain structure in the context of eating. In this review, we summarize recent findings in the fast growing body of literature in the field and provide an overview of technical aspects as well as the basic brain mechanisms identified with imaging. Furthermore, we highlight findings linking neural processing of eating-related stimuli with obesity.

RECENT FINDINGS

The consumption of food is based on a complex interplay between homeostatic and hedonic mechanisms. Several hormones influence brain activity to regulate food intake and interact with the brain's reward circuitry, which is partly mediated by dopamine signaling. Additionally, it was shown that food stimuli trigger cognitive control mechanisms that incorporate internal goals into food choice. The brain mechanisms observed in this context are strongly influenced by genetic factors, sex and personality traits.

SUMMARY

Overall, a complex picture arises from brain-imaging findings, because a multitude of factors influence human food choice. Although several key mechanisms have been identified, there is no comprehensive model that is able to explain the behavioral observations to date. Especially a careful characterization of patients according to genotypes and phenotypes could help to better understand the current and future findings in neuroimaging studies.

Neural dynamics in response to binary taste mixtures

Taste stimuli encountered in the natural environment are usually combinations of multiple tastants. Although a great deal is known about how neurons in the taste system respond to single taste stimuli in isolation, less is known about how the brain deals with such mixture stimuli. Here, we probe the responses of single neurons in primary gustatory cortex (GC) of awake rats to an array of taste stimuli including 100% citric acid (100 mM), 100% sodium chloride (100 mM), 100% sucrose (100 mM), and a range of binary mixtures (90/10, 70/30, 50/50, 30/70, and 10/90%). We tested for the presence of three different hypothetical response patterns: 1) responses varying monotonically as a function of concentration of sucrose (or acid) in the mixture (the "monotonic" pattern); 2) responses increasing or decreasing as a function of degree of mixture of the stimulus (the "mixture" pattern); and 3) responses that change abruptly from being similar to one pure taste to being similar the other (the "categorical" pattern). Our results demonstrate the presence of both monotonic and mixture patterns within responses of GC neurons. Specifically, further analysis (that included the presentation of 50 mM sucrose and citric acid) made it clear that mixture suppression reliably precedes a palatability-related pattern. The temporal dynamics of the emergence of the palatability-related pattern parallel the temporal dynamics of the emergence of preference behavior for the same mixtures as measured by a brief access test. We saw no evidence of categorical coding.

Physiological and psychosocial age-related changes associated with reduced food intake in older persons

Dietary intake changes during the course of aging. Normally an increase in food intake is observed around 55 years of age, which is followed by a reduction in food intake in individuals over 65 years of age. This reduction in dietary intake results in lowered levels of body fat and body weight, a phenomenon known as anorexia of aging. Anorexia of aging has a variety of consequences, including a decline in functional status, impaired muscle function, decreased bone mass, micronutrient deficiencies, reduced cognitive functions, increased hospital admission and even premature death. Several changes during lifetime have been implicated to play a role in the reduction in food intake and the development of anorexia of aging. These changes are both physiological, involving peripheral hormones, senses and central brain regulation and non-physiological, with differences in psychological and social factors. In the present review, we will focus on age-related changes in physiological and especially non-physiological factors, that play a role in the age-related changes in food intake and in the etiology of anorexia of aging. At the end we conclude with suggestions for future nutritional research to gain greater understanding of the development of anorexia of aging which could lead to earlier detection and better prevention.