Neural correlates of taste reactivity in autism spectrum disorder

Taste processing in autism spectrum disorder: A translational scoping review

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by persistent challenges in social communication and restricted/repetitive behaviors, including sensory atypicalities. Taste processing is critical for assessing the sensory and hedonic properties of food; however, it remains understudied in ASD, which may limit our understanding of the disorder's links to selective eating and nutritional deficits. This scoping review on autistic gustatory functioning followed a predefined protocol. We conducted searches across four databases and identified 37 studies involving human participants, categorized into three methodologies: questionnaires, neuroimaging, and psychophysical tests. Additionally, eight studies on ASD animal models were included to offer cross-species insights. Questionnaire data generally indicate that individuals with ASD exhibit differences in taste reactivity compared to those without ASD. Neuroimaging studies suggest potential involvement of specific brain regions, including hippocampal volume and anterior superior temporal sulcus (aSTS) connectivity in atypical taste processing. Psychophysical assessments and animal studies further reveal variability in basic taste preferences, with individuals with ASD showing particular aversion to bitterness and showing either no difference or a decreased preference for sweetness compared to typically developing peers. This review also highlights research gaps regarding specific qualitative tastes such as saltiness, sourness, and umami in ASD, limiting a comprehensive understanding of ASD's chemosensory profile and emphasizing the need for further research in these areas.

Automatic engagement of limbic and prefrontal networks in response to food images reflects distinct information about food hedonics and inhibitory control

Adaptive regulation of food consumption involves both identifying food as well as evaluating whether it should be eaten, a process that requires assessing relevant properties such as healthfulness and hedonic value. In order to identify how these fine-grained food properties are represented in the brain, we analyzed functional Magnetic Resonance Imaging data from 43 participants who viewed images of 36 different foods. A data-driven clustering approach based on Representational Similarity Analysis partitioned food-responsive brain regions into two sub-networks based on their multivariate response to food pictures: a Prefrontal network composed of fronto-parietal brain regions and a Limbic network composed of cortico-limbic and sub-cortical brain regions. Further analysis, using similarity judgments of those foods from a large online sample, revealed that the Prefrontal network predominantly represented information related to food healthfulness or processing, the key factor underlying food similarity. In another imaging task, we found that responses in the Prefrontal network were strongly influenced by judgments of food-related self-control, while the Limbic network responses were more affected by hedonic food judgments. These results suggest that, upon viewing food images, behaviorally relevant information is automatically retrieved from distinct brain networks that act as opponent processes in guiding food consumption.

Dental Adaptation Strategies for Children with Autism Spectrum Disorder-A Systematic Review of Randomized Trials

Background: Children with Autism Spectrum Disorder (ASD) often struggle with dental care due to sensory sensitivities and behavioral issues, increasing their risk for oral health problems. Adaptation strategies such as visual aids, video modeling, and sensory-adapted environments aim to improve their dental experiences. Methods: A systematic review of randomized controlled trials (RCTs) was conducted according to PRISMA 2020 guidelines using the PubMed, Scopus, Embase, and Cochrane databases. Of the 1072 records screened, nine RCTs were included in the analysis. Studies included children with ASD under 18 years and compared dental adaptation techniques with traditional care. The risk of bias and study quality were assessed. The quality of evidence for the results was determined using the GRADE tool. Results: Nine RCTs with sample sizes ranging from 25 to 138 participants showed significant improvements in oral hygiene, reduced anxiety, and increased cooperation. Video modeling and sensory-adapted environments were particularly effective in lowering distress during dental visits. Conclusions: Dental adaptation strategies, especially video modeling and sensory-adapted environments, effectively improve oral health outcomes and reduce anxiety in children with ASD. More research is needed to explore the long-term effects and include children with severe ASD.

Altered Functional Connectivity of Unimodal Sensory and Multisensory Integration Networks Is Related to Symptom Severity in Autism Spectrum Disorder

BACKGROUND

Atypical sensory processing is a prevalent feature of autism spectrum disorder (ASD) and constitutes a core diagnostic criterion in DSM-5. However, the neurocognitive underpinnings of atypical unimodal and multimodal sensory processing and their relationships with autism symptoms remain unclear.

METHODS

In this study, we examined intrinsic functional connectivity (FC) patterns among 5 unimodal sensory and multisensory integration (MSI) networks in ASD using a large multisite dataset (N = 646) and investigated the relationships between altered FC, atypical sensory processing, social communicative deficits, and overall autism symptoms using correlation and mediation analyses.

RESULTS

Compared with typically developing control participants, participants in the ASD group demonstrated increased FC of the olfactory network, decreased FC within the MSI network, and decreased FC of the MSI-unimodal sensory networks. Furthermore, altered FC was positively associated with autism symptom severity, and such associations were completely mediated by atypical sensory processing and social communicative deficits.

CONCLUSIONS

ASD-specific olfactory overconnectivity and MSI-unimodal sensory underconnectivity lend support to the intense world theory and weak central coherence theory, suggesting olfactory hypersensitivity at the expense of MSI as a potential neural mechanism underlying atypical sensory processing in ASD. These atypical FC patterns suggest potential targets for psychological and neuromodulatory interventions.

Superior temporal sulcus folding, functional network connectivity, and autistic-like traits in a non-clinical population

BACKGROUND

Autistic-like traits (ALT) are prevalent across the general population and might be linked to some facets of a broader autism spectrum disorder (ASD) phenotype. Recent studies suggest an association of these traits with both genetic and brain structural markers in non-autistic individuals, showing similar spatial location of findings observed in ASD and thus suggesting a potential neurobiological continuum.

METHODS

In this study, we first tested an association of ALTs (assessed with the AQ questionnaire) with cortical complexity, a cortical surface marker of early neurodevelopment, and then the association with disrupted functional connectivity. We analysed structural T1-weighted and resting-state functional MRI scans in 250 psychiatrically healthy individuals without a history of early developmental disorders, in a first step using the CAT12 toolbox for cortical complexity analysis and in a second step we used regional cortical complexity findings to apply the CONN toolbox for seed-based functional connectivity analysis.

RESULTS

Our findings show a significant negative correlation of both AQ total and AQ attention switching subscores with left superior temporal sulcus (STS) cortical folding complexity, with the former being significantly correlated with STS to left lateral occipital cortex connectivity, while the latter showed significant positive correlation of STS to left inferior/middle frontal gyrus connectivity (n = 233; all p < 0.05, FWE cluster-level corrected). Additional analyses also revealed a significant correlation of AQ attention to detail subscores with STS to left lateral occipital cortex connectivity.

LIMITATIONS

Phenotyping might affect association results (e.g. choice of inventories); in addition, our study was limited to subclinical expressions of autistic-like traits.

CONCLUSIONS

Our findings provide further evidence for biological correlates of ALT even in the absence of clinical ASD, while establishing a link between structural variation of early developmental origin and functional connectivity.

Neural Hyperresponsivity During the Anticipation of Tangible Social and Nonsocial Rewards in Autism Spectrum Disorder: A Concurrent Neuroimaging and Facial Electromyography Study

BACKGROUND

Atypical anticipation of social reward has been shown to lie at the core of the social challenges faced by individuals with autism spectrum disorder (ASD). However, previous research has yielded inconsistent results and has often overlooked crucial characteristics of stimuli. Here, we investigated ASD reward processing using social and nonsocial tangible stimuli, carefully matched on several key dimensions.

METHODS

We examined the anticipation and consumption of social (interpersonal touch) and nonsocial (flavored milk) rewards in 25 high-functioning individuals with ASD and 25 neurotypical adult individuals. In addition to subjective ratings of wanting and liking, we measured physical energetic expenditure to obtain the rewards, brain activity with neuroimaging, and facial reactions through electromyography on a trial-by-trial basis.

RESULTS

Participants with ASD did not exhibit reduced motivation for social or nonsocial rewards; their subjective ratings, motivated efforts, and facial reactions were comparable to those of neurotypical participants. However, anticipation of higher-value rewards increased neural activation in lateral parietal cortices, sensorimotor regions, and the orbitofrontal cortex. Moreover, participants with ASD exhibited hyperconnectivity between frontal medial regions and occipital regions and the thalamus.

CONCLUSIONS

Individuals with ASD who experienced rewards with tangible characteristics, whether social or nonsocial, displayed typical subjective and objective motivational and hedonic responses. Notably, the observed hyperactivations in sensory and attentional nodes during anticipation suggest atypical sensory overprocessing of forthcoming rewards rather than decreased reward value. While these atypicalities may not have manifested in observable behavior here, they could impact real-life social interactions that require nuanced predictions, potentially leading to the misperception of reduced interest in rewarding social stimuli in ASD.

Naturalistic food categories are driven by subjective estimates rather than objective measures of food qualities

Food-related studies often categorize foods using criteria such as fat and sugar content (e.g., high-fat, high-sugar foods; low-fat, low-sugar foods), and use these categorizations for further analyses. While these criteria are relevant to nutritional health, it is unclear whether they agree with the ways in which we typically group foods. Do these objective categories correspond to our subjective sense? To address this question, we recruited a group of 487 online participants to perform a triplet comparison task involving implicit object similarity judgements on images of 36 foods, which varied in their levels of fat and sugar. We also acquired subjective ratings of other food properties from another set of 369 online participants. Data from the online triplet task was used to generate a similarity matrix of these 36 foods. Principal Components Analysis (PCA) of this matrix identified that the strongest determinant of food similarity (the first PC) was most highly related to participants' judgements of how processed the foods were, while the second component was most related to estimates of sugar and fat content. K-means clustering analysis revealed five emergent food groupings along these PC axes: sweets, fats, starches, fruits, and vegetables. Our results suggest that naturalistic categorizations of food are driven primarily by knowledge of the origin of foods (i.e., grown or manufactured), rather than by their sensory or macronutrient properties. These differences should be considered and explored when developing methods for scientific food studies.

The Sensory Profiles, Eating Behaviors, and Quality of Life of Children with Autism Spectrum Disorder and Avoidant/Restrictive Food Intake Disorder

Eating disorders frequently accompany autism spectrum disorder (ASD). One such novel eating disorder is avoidant/restrictive food intake disorder (ARFID). This study compares the eating attitudes, quality of life, and sensory processing of typically developing children (TDC), autistic children, and autistic children with ARFID. A total of 111 children aged 4-10 with a diagnosis of ASD and ARFID (n = 37), ASD without ARFID (n = 37), and typical development (n = 37) were recruited. After an interview in which Childhood Autism Rating Scale (CARS) was administered, Child Eating Behavior Questionnaire (CEBQ), Pediatric Quality of Life Inventory (PedsQL), Social Responsiveness Scale (SRS) and Sensory Profile (SP) were completed by caregivers. Autistic children with ARFID had higher scores in CEBQ subscales relating to low appetite and lower scores on the subscales associated with weight gain. Both groups of autistic children scored lower than TDC on all PedsQL subscales and autistic children with ARFID had lower social QL scores than both groups. SRS scores were highest in autistic children with ARFID, followed by autistic and typically developing children. CARS scores were similar in both groups of autistic children, but higher than TDC. Auditory, vision, touch, multi-sensory, oral processing scores; as well as all quadrant scores, were significantly lower in autistic children with ARFID. Oral sensory processing scores were found to be the most significant predictor of ARFID comorbidity in ASD and reliably predicted ARFID in autistic children in the clinical setting. Autistic children with ARFID demonstrate differences in social functioning, sensory processing, eating attitudes, and quality of life compared to autistic and TD children.

Eating and Sensory Features of Children With Autism Spectrum Disorder and Their Typically Developing Peers

IMPORTANCE

Impaired sensory processing is associated with eating problems. There seem to be no previous studies that compare those who have autism spectrum disorder (ASD) with eating problems (ASD-W) and those with ASD without eating problems (ASD-WO) with typically developing (TD) groups. Comparisons are expected to provide further knowledge to guide the intervention programs.

OBJECTIVE

To investigate differences among ASD-W, ASD-WO, and TD groups in eating and sensory features; to detect associations between sensory and eating behaviors and any most involved sensory dimensions; and to search for age-related differences in sensory and eating features in ASD.

DESIGN

Nonrandomized comparison study.

SETTING

Questionnaires administered as parent interviews.

PARTICIPANTS

A total of 165 children were recruited: 117 with ASD and 48 TD children.

OUTCOMES AND MEASURES

Standardized questionnaires: the Brief Autism Mealtime Behaviors Inventory for eating problems; the Short Sensory Profile and the Sensory Experience Questionnaire for sensory problems.

RESULTS

The ASD-W group showed generalized, impaired eating behaviors and turned out to be the most impaired with regard to sensory responsiveness. No differences in feeding behaviors were found between the ASD-WO and TD groups. All children with ASD showed sensory hyper- or hyporesponsiveness. Four main sensory dimensions were found to be associated with eating behaviors in ASD. No age differences were found in the eating and sensory behaviors of children with ASD.

CONCLUSIONS AND RELEVANCE

Differing eating and sensory profiles were found between the ASD and TD groups, especially in children with ASD-W. Early eating interventions using sensory stimulations are strongly recommended. What This Article Adds: This study reports novel information derived from the comparisons of children with ASD with eating problems and those with ASD without eating problems with typically developing groups of children.

A working taxonomy for describing the sensory differences of autism

BACKGROUND

Individuals on the autism spectrum have been long described to process sensory information differently than neurotypical individuals. While much effort has been leveraged towards characterizing and investigating the neurobiology underlying the sensory differences of autism, there has been a notable lack of consistency in the terms being used to describe the nature of those differences.

MAIN BODY

We argue that inconsistent and interchangeable terminology-use when describing the sensory differences of autism has become problematic beyond mere pedantry and inconvenience. We begin by highlighting popular terms that are currently being used to describe the sensory differences of autism (e.g. "sensitivity", "reactivity" and "responsivity") and discuss why poor nomenclature may hamper efforts towards understanding the aetiology of sensory differences in autism. We then provide a solution to poor terminology-use by proposing a hierarchical taxonomy for describing and referring to various sensory features.

CONCLUSION

Inconsistent terminology-use when describing the sensory features of autism has stifled discussion and scientific understanding of the sensory differences of autism. The hierarchical taxonomy proposed was developed to help resolve lack of clarity when discussing the sensory differences of autism and to place future research targets at appropriate levels of analysis.

Insights on dental care management and prevention in children with autism spectrum disorder (ASD). What is new?

Autistic subjects represent a severe concern to dentistry due to the considerable difficulty in managing their oral health, maintaining routine toothbrushing, and preventing dental and periodontal problems. The social and economic burden of managing dental care in autism spectrum disorder (ASD) children is particularly cumbersome for families and public and private health expenditure, especially when children reach the dentist following a late diagnosis with evident oral health problems. An early diagnosis of ASD helps dentists better address these children's oral health. Unfortunately, insufficient attention is paid to the training and education of general pediatricians, dentists, and dental hygienists, allowing them to get to approach the different clinical aspects of ASD. Usually, children diagnosed with ASD are scheduled for dental appointments like their neurotypical peers, whereas their needs are typically complex and personalized. Scant attention is also devoted to these patients by commercial manufacturers of dental products and devices for oral hygiene and prevention of caries and periodontal diseases, leaving parents without the support and often failing when they address the oral health of autistic children. The difficulties of oral care do not derive simply from the behavior of ASD patients, as is commonly assumed, and therefore cannot be overcome solely by the patience and attention of parents and dentists. Genetics, dietary habits, sensory impairments, and cognition disorders are other causes contributing in various degrees to the impact on the mood and psychological reactions of autistic children towards dentists. How can we prevent teeth caries, periodontal disorders, and other oral health impairments by properly managing ASD children? This manuscript gives an up-to-date overview of these problems and helps to provide good remarks.

Oxytocin and cardiometabolic interoception: Knowing oneself affects ingestive and social behaviors

Maintaining homeostasis while navigating one's environment involves accurately assessing and interacting with external stimuli while remaining consciously in tune with internal signals such as hunger and thirst. Both atypical social interactions and unhealthy eating patterns emerge as a result of dysregulation in factors that mediate the prioritization and attention to salient stimuli. Oxytocin is an evolutionarily conserved peptide that regulates attention to exteroceptive and interoceptive stimuli in a social environment by functioning in the brain as a modulatory neuropeptide to control social behavior, but also in the periphery as a hormone acting at oxytocin receptors (Oxtr) expressed in the heart, gut, and peripheral ganglia. Specialized sensory afferent nerve endings of Oxtr-expressing nodose ganglia cells transmit cardiometabolic signals via the Vagus nerve to integrative regions in the brain that also express Oxtr(s). These brain regions are influenced by vagal sensory pathways and coordinate with external events such as those demanding attention to social stimuli, thus the sensations related to cardiometabolic function and social interactions are influenced by oxytocin signaling. This review investigates the literature supporting the idea that oxytocin mediates the interoception of cardiovascular and gastrointestinal systems, and that the modulation of this awareness likewise influences social cognition. These concepts are then considered in relation to Autism Spectrum Disorder, exploring how atypical social behavior is comorbid with cardiometabolic dysfunction.

Functional Connectivity of the Chemosenses: A Review

Functional connectivity approaches have long been used in cognitive neuroscience to establish pathways of communication between and among brain regions. However, the use of these analyses to better understand how the brain processes chemosensory information remains nascent. In this review, we conduct a literature search of all functional connectivity papers of olfaction, gustation, and chemesthesis, with 103 articles discovered in total. These publications largely use approaches of seed-based functional connectivity and psychophysiological interactions, as well as effective connectivity approaches such as Granger Causality, Dynamic Causal Modeling, and Structural Equation Modeling. Regardless of modality, studies largely focus on elucidating neural correlates of stimulus qualities such as identity, pleasantness, and intensity, with task-based paradigms most frequently implemented. We call for further "model free" or data-driven approaches in predictive modeling to craft brain-behavior relationships that are free from a priori hypotheses and not solely based on potentially irreproducible literature. Moreover, we note a relative dearth of resting-state literature, which could be used to better understand chemosensory networks with less influence from motion artifacts induced via gustatory or olfactory paradigms. Finally, we note a lack of genomics data, which could clarify individual and heritable differences in chemosensory perception.

Evaluating the Use of Self-reported Measures in Autistic Individuals in the Context of Psychiatric Assessment: A Systematic Review

The current review examined the use of self-report measures in autistic individuals in the context of psychiatric assessments. It focused on inter-rater agreement, internal consistency, test-retest reliability, and criterion validity with clinical diagnoses. It also gathered information on constructs measured, the nature of the samples, and the quality of the studies. Thirty-six out of 10,557 studies met inclusion criteria. We found that the majority of studies (1) targeted young people with average or above average cognitive abilities, (2) measured anxiety symptoms, and (3) evaluated parent-child agreement. More studies are needed on individuals with lower cognitive abilities, adults, and other constructs. Studies assessing criterion validity and test-retest reliability are also needed.

Perception and Motion in Real and Virtual Environments: A Narrative Review of Autism Spectrum Disorders

Atypical sensorimotor developmental trajectories greatly contribute to the profound heterogeneity that characterizes Autism Spectrum Disorders (ASD). Individuals with ASD manifest deviations in sensorimotor processing with early markers in the use of sensory information coming from both the external world and the body, as well as motor difficulties. The cascading effect of these impairments on the later development of higher-order abilities (e.g., executive functions and social communication) underlines the need for interventions that focus on the remediation of sensorimotor integration skills. One of the promising technologies for such stimulation is Immersive Virtual Reality (IVR). In particular, head-mounted displays (HMDs) have unique features that fully immerse the user in virtual realities which disintegrate and otherwise manipulate multimodal information. The contribution of each individual sensory input and of multisensory integration to perception and motion can be evaluated and addressed according to a user’s clinical needs. HMDs can therefore be used to create virtual environments aimed at improving people’s sensorimotor functioning, with strong potential for individualization for users. Here we provide a narrative review of the sensorimotor atypicalities evidenced by children and adults with ASD, alongside some specific relevant features of IVR technology. We discuss how individuals with ASD may interact differently with IVR versus real environments on the basis of their specific atypical sensorimotor profiles and describe the unique potential of HMD-delivered immersive virtual environments to this end.

Viewing images of foods evokes taste quality-specific activity in gustatory insular cortex

Previous studies have shown that the conceptual representation of food involves brain regions associated with taste perception. The specificity of this response, however, is unknown. Does viewing pictures of food produce a general, nonspecific response in taste-sensitive regions of the brain? Or is the response specific for how a particular food tastes? Building on recent findings that specific tastes can be decoded from taste-sensitive regions of insular cortex, we asked whether viewing pictures of foods associated with a specific taste (e.g., sweet, salty, and sour) can also be decoded from these same regions, and if so, are the patterns of neural activity elicited by the pictures and their associated tastes similar? Using ultrahigh-resolution functional magnetic resonance imaging at high magnetic field strength (7-Tesla), we were able to decode specific tastes delivered during scanning, as well as the specific taste category associated with food pictures within the dorsal mid-insula, a primary taste responsive region of brain. Thus, merely viewing food pictures triggers an automatic retrieval of specific taste quality information associated with the depicted foods, within gustatory cortex. However, the patterns of activity elicited by pictures and their associated tastes were unrelated, thus suggesting a clear neural distinction between inferred and directly experienced sensory events. These data show how higher-order inferences derived from stimuli in one modality (i.e., vision) can be represented in brain regions typically thought to represent only low-level information about a different modality (i.e., taste).

The Impact of Atypical Sensory Processing on Adaptive Functioning and Maladaptive Behaviors in Autism Spectrum Disorder During Childhood: Results From the ELENA Cohort

Atypical sensory processing is common in autism spectrum disorders (ASD), but their role in adaptive difficulties and problem behaviors is poorly understood. Our aim was to determine the prevalence and type of atypical sensory processing in children with ASD and investigate its impact on their adaptive functioning and maladaptive behaviors. We studied a subsample of 197 children rigorously diagnosed with ASD from the ELENA cohort. Children were divided into atypical and typical sensory processing groups and several independent variables were compared, including adaptive functioning and maladaptive behaviors. Overall, 86.8% of the children had at least one atypical sensory pattern and all sensory modalities were disturbed. Atypical sensory processing explained a significant part of the variance of behavioral problems.

Sensory Profiles of Children with Autism Spectrum Disorder with and without Feeding Problems: A Comparative Study in Sicilian Subjects

The aim of this study is to better understand the relationship between sensory and feeding problems in Autism Spectrum Disorder (ASD) by comparing sensory responsiveness of ASD children with (ASD-W) and without (ASD-WO) feeding problems. The feeding and sensory characteristics of 111 children with ASD (37 ASD-W and 74 ASD-WO) were assessed by using two questionnaires tapping on feeding problems and two on sensory problems. A comparative study was carried out with between-group as well as intra-group comparisons design; a correlation analysis was also added. A statistically significant correlation was found between sensory and feeding problems. ASD-W children showed more severe and extensively impaired sensory responses than ASD-WO, with lower sensory adaptation and more generalized and severe deficits in all subdomains. Taste/Smell sensitivity was strongly impaired only in ASD-W, whereas in ASD-WO it was found to be a point of strength. Both groups showed a Hyporesponsive profile, though it was more marked in ASD-W. Both groups showed strengths in Visual/Auditory sensitivity, Low-Energy/Weak, and Movement sensitivity, again more marked in ASD-WO. These results might prove to be particularly useful for sensory training and psychoeducational treatment.

Visual Body Part Representation in the Lateral Occipitotemporal Cortex in Children/Adolescents and Adults

The lateral occipitotemporal cortex (LOTC) that responds to human bodies and body parts has been implicated in social development and neurodevelopmental disorders like autism spectrum disorder (ASD). Neuroimaging studies using a representational similarity analysis (RSA) revealed that body representation in the LOTC of typically developing (TD) adults is categorized into 3 clusters: action effector body parts, noneffector body parts, and face parts. However, its organization of younger people (i.e., children and adolescents) and its association with individual traits remain unclear. In this functional MRI study, TD adults and children/adolescents observed photographs of hands, feet, arms, legs, chests, waists, upper/lower faces, the whole body, and chairs. The univariate analysis showed that fewer child/adolescent participants showed left LOTC activation in response to whole-body images (relative to those of chairs) than adult participants. Contrastingly, the RSA on both age groups revealed a comparable body representation with 3 clusters of body parts in the bilateral LOTC. Hence, this result indicates that, although response to whole-body images can differ, LOTC body part representations for children/ adolescents and adults are highly similar. Furthermore, sensory atypicality is associated with spatial LOTC organization, suggesting the importance of this region for understanding individual difference, which is frequently observed in ASD.

Dietary Approaches to the Management of Autism Spectrum Disorders

This chapter reviews the literature surrounding autism spectrum disorders (ASD) and their relation to gastrointestinal (GI), behavioral, neurological, and immunological functioning. Individuals with ASD often have poor GI health, including bowel motility issues, autoimmune and/or other adverse responses to certain foods, and lack of necessary nutrient absorption. These issues may be caused or exacerbated by restrictive behavioral patterns (e.g., preference for sweet and salty foods and/or refusal of healthy foods). Those individuals with GI issues tend to demonstrate more behavioral deficits (e.g., irritability, agitation, hyperactivity) and also tend to have an imbalance in overall gut microbiome composition, thus corroborating several studies that have implicated brain-gut pathways as potential mediators of behavioral dysfunction.We examine the literature regarding dietary approaches to managing ASDs, including elimination diets for gluten, casein, or complex carbohydrates, a ketogenic diet, and a low oxalate diet. We also explore the research examining dietary supplements such as fatty acids, pro- and prebiotics, vitamins, minerals, glutathione, phytochemicals, and hormones. The research on dietary approaches to managing ASDs is limited and the results are mixed. However, a few approaches, such as the gluten-free/casein-free diet, fatty acid supplementation, and pre/probiotics have generally demonstrated improved GI and associated behavioral symptoms. Given that GI issues seem to be overrepresented in ASD populations, and that GI issues have been associated with a number behavioral and neurological deficits, dietary manipulation may offer a cheap and easily implemented approach to improve the lives of those with ASD.

Taste Quality Representation in the Human Brain

In the mammalian brain, the insula is the primary cortical substrate involved in the perception of taste. Recent imaging studies in rodents have identified a "gustotopic" organization in the insula, whereby distinct insula regions are selectively responsive to one of the five basic tastes. However, numerous studies in monkeys have reported that gustatory cortical neurons are broadly-tuned to multiple tastes, and tastes are not represented in discrete spatial locations. Neuroimaging studies in humans have thus far been unable to discern between these two models, though this may be because of the relatively low spatial resolution used in taste studies to date. In the present study, we examined the spatial representation of taste within the human brain using ultra-high resolution functional magnetic resonance imaging (MRI) at high magnetic field strength (7-tesla). During scanning, male and female participants tasted sweet, salty, sour, and tasteless liquids, delivered via a custom-built MRI-compatible tastant-delivery system. Our univariate analyses revealed that all tastes (vs tasteless) activated primary taste cortex within the bilateral dorsal mid-insula, but no brain region exhibited a consistent preference for any individual taste. However, our multivariate searchlight analyses were able to reliably decode the identity of distinct tastes within those mid-insula regions, as well as brain regions involved in affect and reward, such as the striatum, orbitofrontal cortex, and amygdala. These results suggest that taste quality is not represented topographically, but by a distributed population code, both within primary taste cortex as well as regions involved in processing the hedonic and aversive properties of taste.SIGNIFICANCE STATEMENT The insula is the primary cortical substrate involved in taste perception, yet some question remains as to whether this region represents distinct tastes topographically or via a population code. Using high field (7-tesla), high-resolution functional magnetic resonance imaging in humans, we examined the representation of different tastes delivered during scanning. All tastes activated primary taste cortex within the bilateral mid-insula, but no brain region exhibited any consistent taste preference. However, multivariate analyses reliably decoded taste quality within the bilateral mid-insula as well as the striatum, orbitofrontal cortex, and bilateral amygdala. This suggests that taste quality is represented by a spatial population code within regions involved in sensory and appetitive properties of taste.