Sexually dimorphic functional connectivity in response to high vs. low energy-dense food cues in obese humans: an fMRI study

Influence of insulin sensitivity on food cue evoked functional brain connectivity in children

Objective

Insulin resistance during childhood is a risk factor for developing type 2 diabetes and other health problems later in life. Studies in adults have shown that insulin resistance affects regional and network activity in the brain which are vital for behavior, e.g. ingestion and metabolic control. To date, no study has investigated whether brain responses to food cues in children are associated with peripheral insulin sensitivity.

Methods

We included 53 children (36 girls) between the age of 7-11 years, who underwent an oral Glucose Tolerance Test (oGTT) to estimate peripheral insulin sensitivity (ISI). Brain responses were measured using functional magnetic resonance imaging (fMRI) before and after glucose ingestion. We compared food-cue task-based activity and functional connectivity (FC) between children with low and high ISI, adjusted for age and BMIz.

Results

Independent of prandial state (i.e., glucose ingestion), children with lower ISI showed higher FC between the anterior insula and caudate and lower FC between the posterior insula and mid temporal cortex than children with higher ISI. Sex differences were found based on prandial state and peripheral insulin sensitivity in the insular FC. No differences were found on whole-brain food-cue reactivity.

Conclusions

Children with low peripheral insulin sensitivity showed differences in food cue evoked response particularly in insula functional connectivity. These differences might influence eating behavior and future risk of developing diabetes.

The influence of the COMT Val158Met polymorphism on prefrontal TDCS effects on aggression

Increasing dorsolateral prefrontal cortex (DLPFC) activity by anodal transcranial direct current stimulation (tDCS) enhances cognitive control and might reduce aggression. The Val158Met polymorphism within the catechol-O-methyltransferase gene (rs4680) plays a pivotal role in prefrontal dopamine signaling, displaying associations with aggressive behavior, and potentially influencing the effects of tDCS. In a double-blind, sham-controlled study, we investigated the influence of rs4680 on tDCS effects on aggression. While undergoing functional magnetic resonance imaging, 89 healthy male participants performed the Taylor aggression paradigm before and immediately after tDCS. Actively stimulated participants (n = 45) received anodal tDCS (1.5 mA) for 20 min targeting the right DLPFC. Carriers of the val-allele (val+; n = 46; active tDCS n = 23) were compared to met-allele homozygotes (val-; n = 43; active tDCS n = 22). Analysis revealed decreased aggressive behavior in the val- group following active tDCS (p < 0.001). The val+ group showed increased aggression during the second session (p < 0.001) with an even higher increase following active as compared to sham tDCS (p < 0.001). No effects of stimulation or rs4680 on brain activation were found. Our study provides evidence for opposite tDCS effects on aggressive behavior in val-carriers and val-noncarriers. By shedding light on genetic factors predicting tDCS responsivity, the study will help to pave the way toward individualized-and thus more effective-tDCS treatment options.

Neuroimaging Investigations of Obesity: a Review of the Treatment of Sex from 2010

PURPOSE OF REVIEW

To summarize the results of adult obesity neuroimaging studies (structural, resting-state, task-based, diffusion tensor imaging) published from 2010, with a focus on the treatment of sex as an important biological variable in the analysis, and identify gaps in sex difference research.

RECENT FINDINGS

Neuroimaging studies have shown obesity-related changes in brain structure, function, and connectivity. However, relevant factors such as sex are often not considered. We conducted a systematic review and keyword co-occurrence analysis. Literature searches identified 6281 articles, of which 199 met inclusion criteria. Among these, only 26 (13%) considered sex as an important variable in the analysis, directly comparing the sexes (n = 10; 5%) or providing single-sex/disaggregated data (n = 16, 8%); the remaining studies controlled for sex (n = 120, 60%) or did not consider sex in the analysis (n = 53, 27%). Synthesizing sex-based results, obesity-related parameters (e.g., body mass index, waist circumference, obese status) may be generally associated with more robust morphological alterations in men and more robust structural connectivity alterations in women. Additionally, women with obesity generally expressed increased reactivity in affect-related regions, while men with obesity generally expressed increased reactivity in motor-related regions; this was especially true under a fed state. The keyword co-occurrence analysis indicated that sex difference research was especially lacking in intervention studies. Thus, although sex differences in the brain associated with obesity are known to exist, a large proportion of the literature informing the research and treatment strategies of today has not specifically examined sex effects, which is needed to optimize treatment.

Effects of prefrontal theta burst stimulation on neuronal activity and subsequent eating behavior: an interleaved rTMS and fNIRS study

The dorsolateral prefrontal cortex (dlPFC) and dorsomedial prefrontal cortex (dmPFC) are both important nodes for self-control and decision-making but through separable processes (cognitive control vs evaluative processing). This study aimed to examine the effects of excitatory brain stimulation [intermittent theta burst stimulation (iTBS)] targeting the dlPFC and dmPFC on eating behavior. iTBS was hypothesized to decrease consumption of appetitive snack foods, via enhanced interference control for dlPFC stimulation and reduced delay discounting (DD) for dmPFC stimulation. Using a single-blinded, between-subjects design, participants (N = 43) were randomly assigned to one of three conditions: (i) iTBS targeting the left dlPFC, (ii) iTBS targeting bilateral dmPFC or (iii) sham. Participants then completed two cognitive tasks (DD and Flanker), followed by a bogus taste test. Functional near-infrared spectroscopy imaging revealed that increases in the medial prefrontal cortex activity were evident in the dmPFC stimulation group during the DD task; likewise, a neural efficiency effect was observed in the dlPFC stimulation group during the Flanker. Gender significantly moderated during the taste test, with females in the dmPFC showing paradoxical increases in food consumption compared to sham. Findings suggest that amplification of evaluative processing may facilitate eating indulgence when preponderant social cues are permissive and food is appetitive.

A systematic and meta-analytic review on the neural correlates of viewing high- and low-calorie foods among normal-weight adults

In the context of current-day online shopping, people select foods based on pictures and using their visual systems. Although there are some reviews of previous neuroimaging studies on appetitive behaviors, the findings on neural activation in response to pictures of high- and low-calorie foods seem inconsistent. This study aims to systematically review, integrate, and meta-analyze neuroimaging evidence of viewing high- and low-calorie foods. There were 25 samples from 24 studies, totalizing 489 normal-weight participants (311 female, 160 male, and 18 of unknown sex). We conducted a systematic review and Activation Likelihood Estimation (ALE) meta-analysis on viewing high-calorie foods (versus non-foods), low-calorie foods (versus non-foods), and high- versus low-calorie foods. In systematic review, several brain regions were shown to be activated when viewing high- or low-calorie foods (versus non-foods) and viewing high- versus low-calorie foods, including the prefrontal cortex, orbitofrontal cortex, amygdala, insula, ventral striatum, hippocampus, superior parietal lobe, and fusiform gyrus. However, the ALE meta-analysis showed that the left orbitofrontal cortex, left amygdala, insula, superior parietal lobe, and fusiform gyrus were activated when viewing high-calorie foods (versus non-foods); the left fusiform gyrus was activated when viewing low-calorie foods (versus non-foods); and no cluster was activated when viewing high- versus low-calorie foods. Our research suggests an appetitive brain network that includes visual perception and attentional processing, sensory input integration, subjective reward value encoding, decision-making, and top-down cognitive control. Future studies should control for the effects of methodological and physiological variables when examining the neural correlates of viewing high- and low-calorie foods.

Regional Neural Activity Abnormalities and Whole-Brain Functional Connectivity Reorganization in Bulimia Nervosa: Evidence From Resting-State fMRI

The management of eating behavior in bulimia nervosa (BN) patients is a complex process, and BN involves activity in multiple brain regions that integrate internal and external functional information. This functional information integration occurs in brain regions involved in reward, cognition, attention, memory, emotion, smell, taste, vision and so on. Although it has been reported that resting-state brain activity in BN patients is different from that of healthy controls, the neural mechanisms remain unclear and need to be further explored. The fractional amplitude of low-frequency fluctuation (fALFF) analyses are an important data-driven method that can measure the relative contribution of low-frequency fluctuations within a specific frequency band to the whole detectable frequency range. The fALFF is well suited to reveal the strength of interregional cooperation at the single-voxel level to investigate local neuronal activity power. FC is a brain network analysis method based on the level of correlated dynamics between time series, which establishes the connection between two spatial regions of interest (ROIs) with the assistance of linear temporal correlation. Based on the psychological characteristics of patients with BN and the abnormal brain functional activities revealed by previous neuroimaging studies, in this study, we investigated alterations in regional neural activity by applying fALFF analysis and whole-brain functional connectivity (FC) in patients with BN in the resting state and to explore correlations between brain activities and eating behavior. We found that the left insula and bilateral inferior parietal lobule (IPL), as key nodes in the reorganized resting-state neural network, had altered FC with other brain regions associated with reward, emotion, cognition, memory, smell/taste, and vision-related functional processing, which may have influenced restrained eating behavior. These results could provide a further theoretical basis and potential effective targets for neuropsychological treatment in patients with BN.

Executive Functions in Predicting Weight Loss and Obesity Indicators: A Meta-Analysis

While previous studies have suggested that there exists a relationship between obesity and executive function (EF), the mechanisms and causal relationship between them remain unclear. There are important clinical implications of determining whether EF can predict and treat obesity. We conducted a multilevel meta-analysis of randomized controlled trials (RCTs) and longitudinal studies. Specifically, we investigate (a) whether EF interventions have an effect on weight loss, (b) whether baseline EF can be a predictor of future weight loss through obesity intervention, and (c) whether early-life EF can predict future weight loss. Eight RCTs and 17 longitudinal studies with a total of 11,393 participants were identified. We found that (a) EF interventions may not have an effect on weight loss, (b) baseline inhibition (β = 0.259, p = 0.03) and delay discounting (β = −0.17, p = 0.04) significantly predict future weight loss through obesity intervention, (c) age (F = 13.666, p = 0.005) moderates the relationship between working memory and weight loss through intervention, but not weight status, type of intervention, and percentage of female, and (d) early life inhibition (β = 0.185, p = 0.07) is a marginally significant predictor of future weight loss. Our results seem to support the assumption that the relationship between EF and obesity is not direct, and a higher-order factor, such as genes, may link obesity and EF. Building on the preliminary findings, further studies focusing on EF and obesity are needed in the future.

Sensory cue reactivity: Sensitization in alcohol use disorder and obesity

Neuroimaging techniques to measure the function of the human brain such as electroencephalography (EEG), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI), are powerful tools for understanding the underlying neural circuitry associated with alcohol use disorder (AUD) and obesity. The sensory (visual, taste and smell) paradigms used in neuroimaging studies represent an ideal platform to investigate the connection between the different neural circuits subserving the reward/executive control systems in these disorders, which may offer a translational mechanism for novel intervention predictions. Thus, the current review provides an integrated summary of the recent neuroimaging studies that have applied cue-reactivity paradigms and neuromodulation strategies to explore underlying alterations in neural circuitry as well in treatment strategies in AUD and obesity. Finally, we discuss literature on mechanisms associated with increased alcohol sensitivity post-bariatric surgery (BS) which offers guidance for future research to use sensory percepts in elucidating the relation of reward signaling in AUD development post-BS.

Abnormal functional connectivity of motor circuit in the schizophrenic patients with tardive dyskinesia: A resting-state fMRI study

BACKGROUND

Animal and neuroimaging studies suggest that the volume of the motor-circuit region decreases in tardive dyskinesia (TD). This study examined the differences in functional connectivity within the motor circuit of patients with schizophrenia with and without TD to further clarify how the dysfunction is related to the pathogenesis of TD.

METHODS

Functional magnetic resonance images were taken of 56 schizophrenic patients with TD (TD group), 64 without TD (non-TD group), and 68 healthy controls (HC group). The motor-circuit area was selected as the seed region for a whole brain resting-state functional connectivity (rsFC) analysis. Psychopathological symptoms and TD severity were assessed with the Positive and Negative Syndrome Scale (PANSS) and Abnormal Involuntary Movement Scale (AIMS), respectively. Group differences and correlations among 18 brain regions of interest (e.g., the global strength of connectivity between two regions) were analyzed.

RESULTS

The analysis of variance results were as follows: The three groups exhibited rsFC losses in the left primary motor cortex, bilateral parietal cortices, right postcentral gyrus, right putamen, right superior parietal lobule, right supplementary motor area and bilateral thalami (false discovery rate,p < 0.05). The TD group showed a significant rsFC loss between the right postcentral gyrus and the inferior frontal gyrus of the left triangular part when compared with the non-TD group (AlphaSim, p < 0.001), which was negatively correlated with the AIMS total score (r=-0.259, p = 0.03).

CONCLUSIONS

These findings may suggest dysfunction of the postcentral and inferior frontal gyri of the triangular part in patients with schizophrenia and TD.

A review of the relationship between eating behavior, obesity and functional brain network organization

Obesity is a major public health issue affecting nearly 40% of American adults and is associated with increased mortality and elevated risk for a number of physical and psychological illnesses. Obesity is associated with impairments in executive functions such as decision making and inhibitory control, as well as in reward valuation, which is thought to contribute to difficulty sustaining healthy lifestyle behaviors, including adhering to a healthy diet. Growing evidence indicates that these impairments are accompanied by disruptions in functional brain networks, particularly those that support self-regulation, reward valuation, self-directed thinking and homeostatic control. Weight-related differences in task-evoked and resting-state connectivity have most frequently been noted in the executive control network (ECN), salience network (SN) and default mode network (DMN), with obesity generally being associated with weakened connectivity in the ECN and enhanced connectivity in the SN and DMN. Similar disruptions have been observed in the much smaller literature examining the relationship between diet and disordered eating behaviors on functional network organization. The purpose of this narrative review was to summarize what is currently known about how obesity and eating behavior relate to functional brain networks, describe common patterns and provide recommendations for future research based on the identified gaps in knowledge.

Neuroimaging of Sex/Gender Differences in Obesity: A Review of Structure, Function, and Neurotransmission

While the global prevalence of obesity has risen among both men and women over the past 40 years, obesity has consistently been more prevalent among women relative to men. Neuroimaging studies have highlighted several potential mechanisms underlying an individual’s propensity to become obese, including sex/gender differences. Obesity has been associated with structural, functional, and chemical alterations throughout the brain. Whereas changes in somatosensory regions appear to be associated with obesity in men, reward regions appear to have greater involvement in obesity among women than men. Sex/gender differences have also been observed in the neural response to taste among people with obesity. A more thorough understanding of these neural and behavioral differences will allow for more tailored interventions, including diet suggestions, for the prevention and treatment of obesity.

Effects of a novel combination of orlistat and acarbose on tolerability, appetite, and glucose metabolism in persons with obesity

OBJECTIVE

There is an unmet medical need for a safe and effective weight loss product with minimal systemic side-effects. In this study, the effect of a novel modified-release fixed-dose combination of orlistat and acarbose (MR-OA) was compared with conventional orlistat (CO) regarding tolerability, appetite and glucose metabolism.

METHODS

Sixty-seven men with obesity, aged 24 to 60 years with body mass indexes (BMIs) 33 to 40 kg m-2 or BMIs 30 to 32 kg m-2 and waist circumference above 102 cm were included. They were randomized to either three different doses of the test formulation MR-OA (60 mg orlistat/20 mg acarbose, 90/30 and 120/40) or CO (Xenical, 120 mg orlistat) for a 2-week study of daily treatment. The participants spent days 1 and 14 at the clinical research centre where they received standardized meals, had blood sampling and filled in questionnaires regarding tolerability and appetite after meals. In days 2 to 13, the participants were at home and continued to fill in the questionnaires daily.

RESULTS

In the MR-OA groups, reports of liquid and oily stools as well as faecal incontinence were fewer, whereas reports of gastric distension and flatulence were higher, compared with the CO group. More participants reported decreased hunger in the 90/30 and 120/40 MR-OA, and postprandial plasma glucose concentration was reduced in all MR-OA groups compared with CO.

CONCLUSIONS

This study shows that by using a modified-release dosage form, orlistat and acarbose can be combined without compromising tolerability. Furthermore, MR-OA shows promising effects regarding reduction of appetite and reduces postprandial glucose. Tolerability is coupled to compliance and thereby efficacy of a treatment; therefore, this novel combination MR-OA could be an effective approach for weight loss treatment. A follow-up study in a more diverse population and for a longer duration with weight loss as primary outcome variable is planned.

History of early life adversity is associated with increased food addiction and sex-specific alterations in reward network connectivity in obesity

BACKGROUND

Neuroimaging studies have identified obesity-related differences in the brain's resting state activity. An imbalance between homeostatic and reward aspects of ingestive behaviour may contribute to obesity and food addiction. The interactions between early life adversity (ELA), the reward network and food addiction were investigated to identify obesity and sex-related differences, which may drive obesity and food addiction.

METHODS

Functional resting state magnetic resonance imaging was acquired in 186 participants (high body mass index [BMI]: ≥25: 53 women and 54 men; normal BMI: 18.50-24.99: 49 women and 30 men). Participants completed questionnaires to assess ELA (Early Traumatic Inventory) and food addiction (Yale Food Addiction Scale). A tripartite network analysis based on graph theory was used to investigate the interaction between ELA, brain connectivity and food addiction. Interactions were determined by computing Spearman rank correlations, thresholded at q < 0.05 corrected for multiple comparisons.

RESULTS

Participants with high BMI demonstrate an association between ELA and food addiction, with reward regions playing a role in this interaction. Among women with high BMI, increased ELA was associated with increased centrality of reward and emotion regulation regions. Men with high BMI showed associations between ELA and food addiction with somatosensory regions playing a role in this interaction.

CONCLUSIONS

The findings suggest that ELA may alter brain networks, leading to increased vulnerability for food addiction and obesity later in life. These alterations are sex specific and involve brain regions influenced by dopaminergic or serotonergic signalling.

A neural signature of metabolic syndrome

That metabolic syndrome (MetS) is associated with age-related cognitive decline is well established. The neurobiological changes underlying these cognitive deficits, however, are not well understood. The goal of this study was to determine whether MetS is associated with regional differences in gray-matter volume (GMV) using a cross-sectional, between-group contrast design in a large, ethnically homogenous sample. T1-weighted MRIs were sampled from the genetics of brain structure (GOBS) data archive for 208 Mexican-American participants: 104 participants met or exceeded standard criteria for MetS and 104 participants were age- and sex-matched metabolically healthy controls. Participants ranged in age from 18 to 74 years (37.3 ± 13.2 years, 56.7% female). Images were analyzed in a whole-brain, voxel-wise manner using voxel-based morphometry (VBM). Three contrast analyses were performed, a whole sample analysis of all 208 participants, and two post hoc half-sample analyses split by age along the median (35.5 years). Significant associations between MetS and decreased GMV were observed in multiple, spatially discrete brain regions including the posterior cerebellum, brainstem, orbitofrontal cortex, bilateral caudate nuclei, right parahippocampus, right amygdala, right insula, lingual gyrus, and right superior temporal gyrus. Age, as shown in the post hoc analyses, was demonstrated to be a significant covariate. A further functional interpretation of the structures exhibiting lower GMV in MetS reflected a significant involvement in reward perception, emotional valence, and reasoning. Additional studies are needed to characterize the influence of MetS's individual clinical components on brain structure and to explore the bidirectional association between GMV and MetS.

Cerebral hunger maps in rodents and humans by diffusion weighted MRI

We design, implement and validate a novel image processing strategy to obtain in vivo maps of hunger stimulation in the brain of mice, rats and humans, combining Diffusion Weighted Magnetic Resonance Imaging (DWI) datasets from fed and fasted subjects. Hunger maps were obtained from axial/coronal (rodents/humans) brain sections containing the hypothalamus and coplanar cortico-limbic structures using Fisher's Discriminant Analysis of the combined voxel ensembles from both feeding situations. These maps were validated against those provided by the classical mono-exponential diffusion model as applied over the same subjects and conditions. Mono-exponential fittings revealed significant Apparent Diffusion Coefficient (ADC) decreases through the brain regions stimulated by hunger, but rigorous parameter estimations imposed the rejection of considerable number of pixels. The proposed approach avoided pixel rejections and provided a representation of the combined DWI dataset as a pixel map of the "Hunger Index" (HI), a parameter revealing the hunger score of every pixel. The new methodology proved to be robust both, by yielding consistent results with classical ADC maps and, by reproducing very similar HI maps when applied to newly acquired rodent datasets. ADC and HI maps demonstrated similar patterns of activation by hunger in hypothalamic and cortico-limbic structures of the brain of rodents and humans, albeit with different relative intensities, rodents showing more intense activations by hunger than humans, for similar fasting periods. The proposed methodology may be easily extended to other feeding paradigms or even to alternative imaging methods.

Brain reactivity to visual food stimuli after moderate-intensity exercise in children

Exercise may play a role in moderating eating behaviors. The purpose of this study was to examine the effect of an acute bout of exercise on neural responses to visual food stimuli in children ages 8-11 years. We hypothesized that acute exercise would result in reduced activity in reward areas of the brain. Using a randomized cross-over design, 26 healthy weight children completed two separate laboratory conditions (exercise; sedentary). During the exercise condition, each participant completed a 30-min bout of exercise at moderate-intensity (~ 67% HR maximum) on a motor-driven treadmill. During the sedentary session, participants sat continuously for 30 min. Neural responses to high- and low-calorie pictures of food were determined immediately following each condition using functional magnetic resonance imaging. There was a significant exercise condition*stimulus-type (high- vs. low-calorie pictures) interaction in the left hippocampus and right medial temporal lobe (p < 0.05). Main effects of exercise condition were observed in the left posterior central gyrus (reduced activation after exercise) (p < 0.05) and the right anterior insula (greater activation after exercise) (p < 0.05). The left hippocampus, right medial temporal lobe, left posterior central gyrus, and right anterior insula appear to be activated by visual food stimuli differently following an acute bout of exercise compared to a non-exercise sedentary session in 8-11 year-old children. Specifically, an acute bout of exercise results in greater activation to high-calorie and reduced activation to low-calorie pictures of food in both the left hippocampus and right medial temporal lobe. This study shows that response to external food cues can be altered by exercise and understanding this mechanism will inform the development of future interventions aimed at altering energy intake in children.

Functional and structural plasticity contributing to obesity: roles for sex, diet, and individual susceptibility

The role of cortico-striatal pathways in cue-triggered motivational processes have been extensively studied. However, recent work has begun to examine the potential contribution of plasticity in these circuits to obesity. Despite the inclusion of women in human obesity studies examining neurobehavioral alterations in cue-triggered motivation, preclinical studies have focused mainly on male subjects. This lack of female subjects in preclinical research had led to a gap in the basic understanding of the neural mechanisms underlying over-eating in females. In this review, we highlight recent work from our lab and others that has begun to elucidate how diet, obesity, and individual susceptibility to weight gain influence functional and structural plasticity within the nucleus accumbens and prefrontal cortex in adult rats. As is the case throughout neuroscience, studies of females or sex differences are largely lacking in this area. Thus, below we describe preliminary neurobehavioral results from female studies in our labs and point out areas for future investigation.

Sex/gender differences in neural correlates of food stimuli: a systematic review of functional neuroimaging studies

Sex and gender differences in food perceptions and eating behaviors have been reported in psychological and behavioral studies. The aim of this systematic review was to synthesize studies that examined sex/gender differences in neural correlates of food stimuli, as assessed by functional neuroimaging. Published studies to 2016 were retrieved and included if they used food or eating stimuli, assessed patients with functional magnetic resonance imaging (fMRI) or positron emission tomography (PET), and compared activation between males and females. Fifteen studies were identified. In response to visual food cues, females, compared to males, showed increased activation in the frontal, limbic, and striatal areas of the brain as well as the fusiform gyrus. Differences in neural response to gustatory stimuli were inconsistent. This body of literature suggests that females may be more reactive to visual food stimuli. However, findings are based on a small number of studies and additional research is needed to establish a more definitive explanation and conclusion.

Sex differences in the influence of body mass index on anatomical architecture of brain networks

Background/Objective

The brain plays a central role in regulating ingestive behavior in obesity. Analogous to addiction behaviors, an imbalance in the processing of rewarding and salient stimuli results in maladaptive eating behaviors that override homeostatic needs. We performed network analysis based on graph theory to examine the association between body mass index (BMI) and network measures of integrity, information flow, and global communication (centrality) in reward, salience and sensorimotor regions, and to identify sex-related differences in these parameters.

Subjects/Methods

Structural and diffusion tensor imaging were obtained in a sample of 124 individuals (61 males and 63 females). Graph theory was applied to calculate anatomical network properties (centrality) for regions of the reward, salience, and sensorimotor networks. General linear models with linear contrasts were performed to test for BMI and sex-related differences in measures of centrality, while controlling for age.

Results

In both males and females, individuals with high BMI (obese and overweight) had greater anatomical centrality (greater connectivity) of reward (putamen) and salience (anterior insula) network regions. Sex differences were observed both in individuals with normal and elevated BMI. In individuals with high BMI, females compared to males showed greater centrality in reward (amygdala, hippocampus, nucleus accumbens) and salience (anterior mid cingulate cortex) regions, while males compared to females had greater centrality in reward (putamen) and sensorimotor (posterior insula) regions.

Conclusions

In individuals with increased BMI, reward, salience, and sensorimotor network regions are susceptible to topological restructuring in a sex related manner. These findings highlight the influence of these regions on integrative processing of food-related stimuli and increased ingestive behavior in obesity, or in the influence of hedonic ingestion on brain topological restructuring. The observed sex differences emphasize the importance of considering sex differences in obesity pathophysiology.

Winning is not enough: ventral striatum connectivity during physical aggression

Social neuroscience studies have shown that the ventral striatum (VS), a highly reward-sensitive brain area, is activated when participants win competitive tasks. However, in these settings winning often entails both avoiding punishment and punishing the opponent. It is thus unclear whether the rewarding properties of winning are mainly associated to punishment avoidance, or if punishing the opponent can be additionally gratifying. In the present paper we explored the neurophysiological correlates of each outcome, aiming to better understand the development of aggression episodes. We previously introduced a competitive reaction time task that separates both effects: in half of the won trials, participants can physically punish their opponent (active trials), whereas in the other half they can only avoid a punishment (passive trials). We performed functional connectivity analysis seeded in the VS to test for differential network interactions in active compared to passive trials. The VS showed greater connectivity with areas involved in reward valuation (orbitofrontal cortex), arousal (dorsal thalamus and posterior insula), attention (inferior occipital gyrus), and motor control (supplementary motor area) in active compared to passive trials, whereas connectivity between the VS and the inferior frontal gyrus decreased. Interindividual variability in connectivity strength between VS and posterior insula was related to aggressive behavior, whereas connectivity between VS and supplementary motor area was related to faster reaction times in active trials. Our results suggest that punishing a provoking opponent when winning might adaptively favor a "competitive state" in the course of an aggressive interaction.

Fat and lean tissue accretion in relation to reward motivation in children

'Reward sensitivity' explains inter-individual differences in the motivation to obtain rewards when reward cues are perceived. This psychobiological trait has been linked to higher consumption of palatable food when exposed to palatable food cues. The current study aims to examine if reward sensitivity explains differences in patterns of fat and lean tissue accretion over time in children. A longitudinal observational study with measurement waves in 2011 (baseline), 2012, 2013, and 2015 was conducted. The sample was a population-based Flemish cohort of children (n = 446, 50% boys and 5.5-12 years at baseline; 38.8% of the baseline sample also participated in 2015). Baseline reward sensitivity of the children was assessed by parent ratings on the Drive subscale of the Behavioral Inhibition System/Behavioral Approach System scales. Age- and sex-independent Fat and Lean Mass Index z-scores (zFMI and zLMI respectively) were computed for each study wave based on air-displacement plethysmography. In girls, but not boys, reward sensitivity was positively associated with the baseline zFMI and zLMI (95% confidence intervals of unstandardized estimates: 0.01 to 0.11 and 0.01 to 0.10 respectively, P values 0.01 and 0.02 respectively). Further, reward sensitivity explained 14.8% and 11.6% of the change in girls' zFMI and zLMI respectively over four years: the zFMI and zLMI increased and decreased respectively in high reward sensitive girls (95% confidence intervals of unstandardized estimates: 0.01 to 0.11 and -0.12 to -0.01 respectively, P values 0.01 and 0.02 respectively). Hence, girls high in reward sensitivity had significantly higher adiposity gain over four years parallel with lower increase in lean mass than was expected on the basis of their age and height. These results may help to identify appropriate targets for interventions for obesity prevention.

Reported appetite, taste and smell changes following Roux-en-Y gastric bypass and sleeve gastrectomy: Effect of gender, type 2 diabetes and relationship to post-operative weight loss

Reduced energy intake drives weight loss following Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) procedures. Post-operative changes in subjective appetite, taste, and smell and food preferences are reported and suggested to contribute to reduced energy intake. We aimed to investigate the prevalence of these changes following RYGB and SG and to evaluate their relationship with weight loss. 98 patients post-RYGB and 155 post-SG from a single bariatric centre were recruited to a cross-sectional study. Participants completed a questionnaire, previously utilised in post-operative bariatric patients, to assess the prevalence of post-operative food aversions and subjective changes in appetite, taste and smell. Anthropometric data were collected and percentage weight loss (%WL) was calculated. The relationship between food aversions, changes in appetite, taste and smell and %WL was assessed. The influence of time post-surgery, gender and type 2 diabetes (T2D) were evaluated. Following RYGB and SG the majority of patients reported food aversions (RYGB = 62%, SG = 59%), appetite changes (RYGB = 91%, SG = 91%) and taste changes (RYGB = 64%, SG = 59%). Smell changes were more common post-RYGB than post-SG (RYGB = 41%, SG = 28%, p = 0.039). No temporal effect was observed post-RYGB. In contrast, the prevalence of appetite changes decreased significantly with time following SG. Post-operative appetite changes associated with and predicted higher %WL post-SG but not post-RYGB. Taste changes associated with and predicted higher %WL following RYGB but not post-SG. There was no gender effect post-RYGB. Post-SG taste changes were less common in males (female = 65%, males = 40%, p = 0.008). T2D status in females did not influence post-operative subjective changes. However, in males with T2D, taste changes were less common post-SG than post-RYGB together with lower %WL (RYGB = 27.5 ± 2.7, SG = 14.6 ± 2.1, p = 0.003). Further research is warranted to define the biology underlying these differences and to individualise treatments.

Sex and estrogens alter the action of glucagon-like peptide-1 on reward

Background

Feeding behavior is regulated through an intricate array of anorexic and orexigenic hormones acting on the central nervous system (CNS). Some of these hormones may have differential effects in males and females, effects potentially attributed to actions of gonadal steroids, especially estrogens. Central stimulation of the glucagon-like peptide-1 (GLP-1) receptors reduces feeding and food-reward behavior by acting on CNS regions important for the anorexic actions of estrogens. Thus, we propose that the action of GLP-1 on food intake and reward may differ between sexes.

Methods

Male and female rats were centrally injected with the GLP-1 analog exendin-4 (Ex4) in a non-deprived or food-restricted state; reward behavior was measured in a progressive ratio operant conditioning task. Intake of chow and palatable food were also measured. To determine if sex differences in the actions of Ex4 are due to interactions with estrogens, Ex4 treatment was preceded by treatment with a nonselective estrogen receptor-α (ERα) and ERβ or ERα-selective antagonist.

Results

Central injection of Ex4 revealed increased reward behavior suppression in females, compared to males, in the operant conditioning task. This increase was present in both non-deprived and food-restricted animals with larger differences in the fed state. Intake of chow and palatable food, after Ex4, were similar in males and females. Food reward, but not food intake, effect of Ex4 was attenuated by pretreatment with ER antagonist in both sexes, suggesting that estrogens may modulate effects of Ex4 in both sexes. Furthermore, central pretreatment with ERα-selective antagonist was sufficient to attenuate effects of Ex4 on reward.

Conclusions

Collectively, these data reveal that females display much higher sensitivity to the food reward impact of central GLP-1 receptor activation. Surprisingly, they also demonstrate that central ERα signaling is necessary for the actions of GLP-1 on food-reward behavior in both sexes.

Heterogeneity in brain reactivity to pleasant and food cues: evidence of sign-tracking in humans

Aberrant brain reward responses to food-related cues are an implied characteristic of human obesity; yet, findings are inconsistent. To explain these inconsistencies, we aimed to uncover endophenotypes associated with heterogeneity in attributing incentive salience to food cues in the context of other emotionally salient cues; a phenomenon described as sign- vs goal tracking in preclinical models. Data from 64 lean and 88 obese adults who were 35.5 ± 9.4 years old and predominantly women (79%) were analyzed. Participants viewed food-related, pleasant, neutral and unpleasant images while recording electroencephalograph. Late positive potentials were used to assess incentive salience attributed to the visual stimuli. Eating and affective traits were also assessed. Findings demonstrated that obese individuals, in general, do not demonstrate aberrant brain reward responses to food-related cues. As hypothesized, latent profile analysis of the late positive potential uncovered two distinct groups. 'Sign-trackers' showed greater responses to food-related cues (P < 0.001) but lower responses to pleasant stimuli (P < 0.001) compared with 'goal-trackers'. There were proportionally more obese than lean 'sign-trackers' (P = 0.03). Obese 'sign-trackers' reported significantly higher levels of emotional eating and food craving (P < 0.001). By examining the heterogeneity in brain reactivity to various emotional stimuli, this translational study highlights the need to consider important neurobehavioral endophenotypes of obesity.

Aberrant mesolimbic dopamine-opiate interaction in obesity

Dopamine and opioid neurotransmitter systems share many functions such as regulation of reward and pleasure. μ-Opioid receptors (MOR) modulate the mesolimbic dopamine system in ventral tegmental area and striatum, key areas implicated in reward. We hypothesized that dopamine and opioid receptor availabilities correlate in vivo and that this correlation is altered in obesity, a disease with altered reward processing. Twenty lean females (mean BMI 22) and 25 non-binge eating morbidly obese females (mean BMI 41) underwent two positron emission tomography scans with [(11)C]carfentanil and [(11)C]raclopride to measure the MOR and dopamine D2 receptor (DRD2) availability, respectively. In lean subjects, the MOR and DRD2 availabilities were positively associated in the ventral striatum (r=0.62, p=0.003) and dorsal caudate nucleus (r=0.62, p=0.004). Moreover, DRD2 availability in the ventral striatum was associated with MOR availability in other regions of the reward circuitry, particularly in the ventral tegmental area. In morbidly obese subjects, this receptor interaction was significantly weaker in ventral striatum but unaltered in the caudate nucleus. Finally, the association between DRD2 availability in the ventral striatum and MOR availability in the ventral tegmental area was abolished in the morbidly obese. The study demonstrates a link between DRD2 and MOR availabilities in living human brain. This interaction is selectively disrupted in mesolimbic dopamine system in morbid obesity. We propose that interaction between the dopamine and opioid systems is a prerequisite for normal reward processing and that disrupted cross-talk may underlie altered reward processing in obesity.

Poor ability to resist tempting calorie rich food is linked to altered balance between neural systems involved in urge and self-control

Background

The loss of self-control or inability to resist tempting/rewarding foods, and the development of less healthful eating habits may be explained by three key neural systems: (1) a hyper-functioning striatum system driven by external rewarding cues; (2) a hypo-functioning decision-making and impulse control system; and (3) an altered insula system involved in the translation of homeostatic and interoceptive signals into self-awareness and what may be subjectively experienced as a feeling.

Methods

The present study examined the activity within two of these neural systems when subjects were exposed to images of high-calorie versus low-calorie foods using functional magnetic resonance imaging (fMRI), and related this activity to dietary intake, assessed by 24-hour recall. Thirty youth (mean BMI = 23.1 kg/m², range = 19.1 - 33.7; age =19.7 years, range = 14 - 22) were scanned using fMRI while performing food-specific go/nogo tasks.

Results

Behaviorally, participants more readily pressed a response button when go trials consisted of high-calorie food cues (HGo task) and less readily pressed the response button when go trials consisted of low-calorie food cues (LGo task). This habitual response to high-calorie food cues was greater for individuals with higher BMI and individuals who reportedly consume more high-calorie foods. Response inhibition to the high-calorie food cues was most difficult for individuals with a higher BMI and individuals who reportedly consume more high-calorie foods. fMRI results confirmed our hypotheses that (1) the "habitual" system (right striatum) was more activated in response to high-calorie food cues during the go trials than low-calorie food go trials, and its activity correlated with participants’ BMI, as well as their consumption of high-calorie foods; (2) the prefrontal system was more active in nogo trials than go trials, and this activity was inversely correlated with BMI and high-calorie food consumption.

Conclusions

Using a cross-sectional design, our findings help increase understanding of the neural basis of one’s loss of ability to self-control when faced with tempting food cues. Though the design does not permit inferences regarding whether the inhibitory control deficits and hyper-responsivity of reward regions are individual vulnerability factors for overeating, or the results of habitual overeating.

Electronic supplementary material

The online version of this article (doi:10.1186/1475-2891-13-92) contains supplementary material, which is available to authorized users.