Functional neuroimaging: a new generation of human brain studies in obesity research

Effects of bariatric surgery and dietary interventions for obesity on brain neurotransmitter systems and metabolism: A systematic review of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies

This systematic review collates studies of dietary or bariatric surgery interventions for obesity using positron emission tomography and single-photon emission computed tomography. Of 604 publications identified, 22 met inclusion criteria. Twelve studies assessed bariatric surgery (seven gastric bypass, five gastric bypass/sleeve gastrectomy), and ten dietary interventions (six low-calorie diet, three very low-calorie diet, one prolonged fasting). Thirteen studies examined neurotransmitter systems (six used tracers for dopamine DRD2/3 receptors: two each for 11 C-raclopride, 18 F-fallypride, 123 I-IBZM; one for dopamine transporter, 123 I-FP-CIT; one used tracer for serotonin 5-HT2A receptor, 18 F-altanserin; two used tracers for serotonin transporter, 11 C-DASB or 123 I-FP-CIT; two used tracer for μ-opioid receptor, 11 C-carfentanil; one used tracer for noradrenaline transporter, 11 C-MRB); seven studies assessed glucose uptake using 18 F-fluorodeoxyglucose; four studies assessed regional cerebral blood flow using 15 O-H2 O (one study also used arterial spin labeling); and two studies measured fatty acid uptake using 18 F-FTHA and one using 11 C-palmitate. The review summarizes findings and correlations with clinical outcomes, eating behavior, and mechanistic mediators. The small number of studies using each tracer and intervention, lack of dietary intervention control groups in any surgical studies, heterogeneity in time since intervention and degree of weight loss, and small sample sizes hindered the drawing of robust conclusions across studies.

Food preferences after bariatric surgery: a review update

Obesity is a serious and global health problem. The multiple complications of obesity reduce quality of life and increase mortality. Bariatric surgery is one of the best treatment options for obesity management. Bariatric surgery helps people reduce their caloric intake by treating the disease of obesity effectively, in part by increasing signaling from the gut to the brain. The most frequent surgical options are Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). There is controversy regarding changes in food preferences and selection after bariatric surgery. In this review, we aim to outline the changes in food intake and selection, clarify the behavior changes in food intake, and assess the potential mechanisms responsible for these changes in patients after bariatric surgery.

Correlation of active contact location with weight gain after subthalamic nucleus deep brain stimulation: a case series

Background

Weight gain (WG) is a frequently reported side effect of subthalamic deep brain stimulation; however, the underlying mechanisms remain unclear. The active contact locations influence the clinical outcomes of subthalamic deep brain stimulation, but it is unclear whether WG is directly associated with the active contact locations. We aimed to determine whether WG is associated with the subthalamic deep brain stimulation active contact locations.

Methods

We enrolled 14 patients with Parkinson’s disease who underwent bilateral subthalamic deep brain stimulation between 2013 and 2019. Bodyweight and body mass index were measured before and one year following the surgery. The Lead-DBS Matlab toolbox was used to determine the active contact locations based on magnetic resonance imaging and computed tomography. We also created sweet spot maps for WG using voxel-wise statistics, based on volume of tissue activation and the WG of each patient. Fluorodeoxyglucose-positron emission tomography data were also acquired before and one year following surgery, and statistical parametric mapping was used to evaluate changes in brain metabolism. We examined which brain regions’ metabolism fluctuation significantly correlated with increased body mass index scores and positron emission tomography data.

Results

One year after surgery, the body mass index increase was 2.03 kg/m². The sweet spots for WG were bilateral, mainly located dorsally outside of the subthalamic nucleus (STN). Furthermore, WG was correlated with increased metabolism in the left limbic and associative regions, including the middle temporal gyrus, inferior frontal gyrus, and orbital gyrus.

Conclusions

Although the mechanisms underlying WG following subthalamic deep brain stimulation are possibly multifactorial, our findings suggest that dorsal stimulation outside of STN may lead to WG. The metabolic changes in limbic and associative cortical regions after STN-DBS may also be one of the mechanisms underlying WG. Further studies are warranted to confirm whether dorsal stimulation outside of STN changes the activities of these cortical regions.

Accurate neuroimaging biomarkers to predict body mass index in adolescents: a longitudinal study

Obesity is often associated with cardiovascular complications. Adolescent obesity is a risk factor for cardiovascular disease in adulthood; thus, intensive management is warranted in adolescence. The brain state contributes to the development of obesity in addition to metabolic conditions, and hence neuroimaging is an important tool for accurately assessing an individual's risk of developing obesity. Here, we aimed to predict body mass index (BMI) progression in adolescents with neuroimaging features using machine learning approaches. From an open database, we adopted 76 resting-state functional magnetic resonance imaging (rs-fMRI) datasets from adolescents with longitudinal BMI scores. Functional connectivity analyses were performed on cortical surfaces and subcortical volumes. We identified baseline functional connectivity features in the prefrontal-, posterior cingulate-, sensorimotor-, and inferior parietal-cortices as significant determinants of BMI changes. A BMI prediction model based on the identified fMRI biomarkers exhibited a high accuracy (intra-class correlation = 0.98) in predicting BMI at the second visit (1~2 years later). The identified brain regions were significantly correlated with the eating disorder-, anxiety-, and depression-related scores. Based on these results, we concluded that these functional connectivity features in brain regions related to eating disorders and emotional processing could be important neuroimaging biomarkers for predicting BMI progression.

Eating Disorders in Frontotemporal Dementia and Alzheimer's Disease: Evaluation of Brain Perfusion Correlates Using 99mTc-HMPAO SPECT with Brodmann Areas Analysis

BACKGROUND

Eating disorders (ED) in dementia represent a significant impairment affecting patients' and caregivers' lives. In frontotemporal dementia (FTD), ED include overeating, sweet food preference, stereotypical eating, and hyperorality, while in Alzheimer's disease (AD), anorexia and appetite loss are the most common ED.

OBJECTIVE

The aim of our study was to highlight Brodmann areas (BAs) implicated specifically in the appearance of ED in FTD and AD.

METHODS

We studied 141 patients, 75 with FTD and 66 with AD. We used the NeuroGamTM software on the reconstructed single photon emission computed tomography-SPECT data for the automated comparison of BAs perfusion on the left (L) and right (R) hemisphere with perfusion in corresponding BAs of a normal database.

RESULTS

The FTD group included 27 men and 48 women, age (mean±SD) 65.8±8.5 years, duration of disease 3.4±3.3 years, Mini-Mental State Examination (MMSE) 17.9±8.6, ED score on Neuropsychiatric Inventory (NPI) 4.7±8.5. ED in FTD were correlated with hypoperfusion in right anterior and dorsolateral prefrontal cortices (BAs 10R, 46R), left orbitofrontal cortex (BA 12L), orbital part of the right inferior frontal gyrus (BA 47R), and left parahippocampal gyrus (BA 36L). The AD group included 21 men and 45 women, age (mean±SD) 70.2±8.0 years, duration of disease 3.3±2.4 years, MMSE 20.2±6, ED-NPI score 2.7±3.9. ED in AD were correlated with hypoperfusion in left inferior temporal cortex (BA 20L).

CONCLUSION

SPECT imaging with automated mapping of brain cortex could contribute to the understanding of the neural networks involved in the manifestation of ED in dementia.

Whole-brain functional connectivity correlates of obesity phenotypes

Dysregulated neural mechanisms in reward and somatosensory circuits result in an increased appetitive drive for and reduced inhibitory control of eating, which in turn causes obesity. Despite many studies investigating the brain mechanisms of obesity, the role of macroscale whole‐brain functional connectivity remains poorly understood. Here, we identified a neuroimaging‐based functional connectivity pattern associated with obesity phenotypes by using functional connectivity analysis combined with machine learning in a large‐scale (n ~ 2,400) dataset spanning four independent cohorts. We found that brain regions containing the reward circuit positively associated with obesity phenotypes, while brain regions for sensory processing showed negative associations. Our study introduces a novel perspective for understanding how the whole‐brain functional connectivity correlates with obesity phenotypes. Furthermore, we demonstrated the generalizability of our findings by correlating the functional connectivity pattern with obesity phenotypes in three independent datasets containing subjects of multiple ages and ethnicities. Our findings suggest that obesity phenotypes can be understood in terms of macroscale whole‐brain functional connectivity and have important implications for the obesity neuroimaging community.

Multivariate association between brain function and eating disorders using sparse canonical correlation analysis

Eating disorder is highly associated with obesity and it is related to brain dysfunction as well. Still, the functional substrates of the brain associated with behavioral traits of eating disorder are underexplored. Existing neuroimaging studies have explored the association between eating disorder and brain function without using all the information provided by the eating disorder related questionnaire but by adopting summary factors. Here, we aimed to investigate the multivariate association between brain function and eating disorder at fine-grained question-level information. Our study is a retrospective secondary analysis that re-analyzed resting-state functional magnetic resonance imaging of 284 participants from the enhanced Nathan Kline Institute-Rockland Sample database. Leveraging sparse canonical correlation analysis, we associated the functional connectivity of all brain regions and all questions in the eating disorder questionnaires. We found that executive- and inhibitory control-related frontoparietal networks showed positive associations with questions of restraint eating, while brain regions involved in the reward system showed negative associations. Notably, inhibitory control-related brain regions showed a positive association with the degree of obesity. Findings were well replicated in the independent validation dataset (n = 34). The results of this study might contribute to a better understanding of brain function with respect to eating disorder.

The orbitofrontal cortex functionally links obesity and white matter hyperintensities

Many studies have linked dysfunction in cognitive control-related brain regions with obesity and the burden of white matter hyperintensities (WMHs). This study aimed to explore how functional connectivity differences in the brain are associated with WMH burden and degree of obesity using resting-state functional magnetic resonance imaging (fMRI) in 182 participants. Functional connectivity measures were compared among four different groups: (1) low WMH burden, non-obese; (2) low WMH burden, obese; (3) high WMH burden, non-obese; and (4) high WMH burden, obese. At a large-scale network-level, no networks showed significant interaction effects, but the frontoparietal network showed a main effect of degree of obesity. At a finer node level, the orbitofrontal cortex showed interaction effects between periventricular WMH burden and degree of obesity. Higher functional connectivity was observed when the periventricular WMH burden and degree of obesity were both high. These results indicate that the functional connectivity of the orbitofrontal cortex is affected by the mutual interaction between the periventricular WMHs and degree of obesity. Our results suggest that this region links obesity with WMHs in terms of functional connectivity.

Cerebral glucose metabolism differs according to future weight change

The brain is known to play a central role in controlling the desire to eat. We aimed to evaluate the brain regions that might have a long-term effect on eating behavior and weight changes. We utilized the data of cognitively normal subjects who are examined by several neurologic tests, and followed-up for 36 months from Alzheimer's Disease Neuroimaging Initiative (ADNI) database, and investigated to search the brain regions that are associated with future weight change. The weight of each subject was measured on each visit at baseline (W0), 36 (W36) months after brain ¹⁸F-Fluorodeoxyglucose (FDG) positron emission tomography (PET). Percentage (%) change of weight was calculated as follows: [(W36-W0)/W0]*100. We classified each subject's change into one of three categories: weight loss, stable, and weight gain. Dynamic 3-dimensional scans of six 5-min frames were acquired 30 mins after injection of 185 MBq of FDG. Image analysis was done using Statistical Parametric Mapping 12. Ninety-six subjects were included in this study (male 54, female 42). Subjects with future weight gain showed hypometabolism in left cerebellum compared with those with future weight loss & stable. Percentage change of weight was positively associated with brain metabolism in right insula, and right caudate nucleus. In conclusion, subjects with future weight gain showed hypometabolism in left cerebellum, and percentage change of weight was positively associated with brain metabolism in right insula, and right caudate nucleus. This study raises the possibility that the brain glucose metabolism precedes the future weight change.

Anger and Coronary Artery Disease in Women Submitted to Coronary Angiography: A 48-Month Follow-Up

Background

Anger control was significantly lower in patients with coronary artery disease (CAD), regardless of traditionally known risk factors, occurrence of prior events or other anger aspects in a previous study of our research group.

Objective

To assess the association between anger and CAD, its clinical course and predictors of low anger control in women submitted to coronary angiography.

Methods

This is a cohort prospective study. Anger was assessed by use of Spielberger’s State-Trait Anger Expression Inventory (STAXI). Women were consecutively scheduled to undergo coronary angiography, considering CAD definition as ≥ 50% stenosis of one epicardial coronary artery.

Results

During the study, 255 women were included, being divided into two groups according to their anger control average (26.99). Those with anger control below average were younger and had a family history of CAD. Patients were followed up for 48 months to verify the occurrence of major cardiovascular events.

Conclusion

Women with CAD undergoing coronary angiography had lower anger control, which was associated with age and CAD family history. On clinical follow-up, event-free survival did not significantly differ between patients with anger control above or below average.

Food-related salience processing in healthy subjects during word recognition: Fronto-parietal network activation as revealed by independent component analysis

BACKGROUND

The study aimed to isolate and localize mutually independent cognitive processes evoked during a word recognition task involving food-related and food-neutral words using independent component analysis (ICA) for continuously recorded EEG data. Recognition memory (old/new effect) involves cognitive subcomponents-familiarity and recollection-which may be temporally and spatially dissociated in the brain. Food words may evoke additional attentional salience which may interact with the old/new effect.

METHODS

Sixteen satiated female participants undertook a word recognition task consisting of an encoding phase (learning of presented words, 40 food-related and 40 food neutral) and a test phase (recognition of previously learned words and new words). Simultaneously recorded 64-channel EEG data were decomposed into mutually independent components using the Infomax algorithm in EEGLAB. The components were localized using single dipole fitting using a four-shell BESA head model. The resulting (nonartefactual) components with <15% residual variance were clustered across subjects using the kmeans algorithm resulting in five meaningful clusters localized to fronto-parietal regions. Repeated-measures anova was employed to test main effects (old/new and food relevance) and their interaction on cluster time courses.

RESULTS

Early task-relevant old/new effects were localized to the medial frontal gyrus (MFG) and later old/new effects to the right parietal regions (precuneus). Food-related (nontask-relevant) salience effects were localized to bilateral parietal regions (left precuneus and right postcentral gyrus). Food-related salience interacted with task relevance, the old/new effect in MFG being significant only for food-neutral words highlighting central the role of MFG as the converging site of endogenous and exogenous salience inputs.

CONCLUSION

Our results indicate ICA to be a valid technique to decompose complex neurophysiological signals involving multiple cognitive processes and implicate the fronto-parietal network as an important attentional network for processing salience and task demands.

Microstructure alterations in the hypothalamus in cranially radiated childhood leukaemia survivors but not in craniopharyngioma patients unaffected by hypothalamic damage

OBJECTIVE

Metabolic complications are frequent in childhood leukaemia (ALL) survivors treated with cranial radiotherapy (CRT). These complications are potentially mediated by damage to the hypothalamus (HT), as childhood onset (CO) craniopharyngioma (CP) survivors without HT involvement are spared overt obesity. Diffusion tensor imaging (DTI) shows brain tissue microstructure alterations, by fractional anisotrophy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD). We used DTI to determine the integrity of the microstructure of the HT in ALL survivors.

DESIGN

Case-control study.

PATIENTS

Three groups were included: (i) 27 CRT treated ALL survivors on hormone supplementation, (ii) 17 CO-CP survivors on hormone supplementation but without HT involvement and (iii) 27 matched controls.

MEASUREMENTS

DTI parameters of the HT were measured and body composition.

RESULTS

Microstructural alterations in the HT were more severe in ALL survivors with a BMI ≥25 than with BMI <25. Compared to controls, ALL survivors had reduced FA (P=.04), increased MD (P<.001), AD (P<.001) and RD (P<.001) in the right and left HT. In the right HT, ALL survivors with a BMI ≥25 showed elevated MD (P=.03) and AD (P=.02) compared to ALL survivors with BMI <25. In contrast, DTI parameters did not differ between CP survivors and controls.

CONCLUSIONS

Long-term follow-up after CRT for ALL DTI measures were affected in the HT despite complete hormone replacement. The present data suggest that ALL survivors have demyelination and axonal loss in the HT.

Functional neuroimaging in obesity

PURPOSE OF REVIEW

This review examines recent advances in the use of functional neuroimaging to study human obesity, a field that is rapidly expanding and continues to be of paramount importance for a better understanding of the pathogenesis of this condition. With rising levels of obesity worldwide and limited therapeutic options, there is a great need for the development of new solutions that can benefit patients.

RECENT FINDINGS

Studies that utilize functional neuroimaging are beginning to shed light on the nature of behavioral and neurocognitive dysfunctions previously identified in individuals with obesity. Significant progress has occurred in the study of reward-related processes, cognition-reward interactions, mechanisms of weight loss, genetic influences and the case of obesity in children and adolescents. Research findings confirm that obesity and its related overeating behaviors are strongly associated with the brain, both at a regional level and a large-scale network level.

SUMMARY

Functional neuroimaging studies bring unprecedented levels of detail to examine the brain basis of obesity and show promise for the development of future brain-based biomarkers and interventions in this condition.

Functional neuroimaging in obesity

PURPOSE OF REVIEW

The review examines recent advances in the use of functional neuroimaging to study human obesity, a field that is rapidly expanding and continues to be of paramount importance for a better understanding of the pathogenesis of this condition. With rising levels of obesity worldwide and limited therapeutic options, there is a great need for the development of new solutions that can benefit patients.

RECENT FINDINGS

Studies that utilize functional neuroimaging are beginning to shed light on the nature of behavioral and neurocognitive dysfunctions previously identified in individuals with obesity. Significant progress has occurred in the study of reward-related processes, cognition-reward interactions, mechanisms of weight loss, genetic influences, and the case of obesity in children and adolescents. Research findings confirm that obesity and its related overeating behaviors are strongly associated with the brain, both at a regional level and a large-scale network level.

SUMMARY

Functional neuroimaging studies bring unprecedented levels of detail to examine the brain basis of obesity, and show promise for the development of future brain-based biomarkers and interventions in this condition.

Voxel-based morphometry reveals brain gray matter volume changes in successful dieters

OBJECTIVE

To compare regional brain volume predictors of percent weight loss (WL) in dieters with obesity (DwO) and in the same participants categorized as "successful" (≥7% WL) or "unsuccessful" dieters (<7% WL).

METHODS

DwO (n = 72) and participants with healthy weight (n = 22) completed a structural MRI at baseline and 3 months. All DwO participants were enrolled in a 12-week program consisting of a reduced calorie diet, increased physical activity, and behavioral modification. SPM8-based voxel-based morphometry processing streams were used for measurements of regional gray (GMV) and white matter volume and longitudinal changes in volume. Correlations between WL and baseline brain volume and change in brain volume, as well as differences between groups, were then tested.

RESULTS

%WL was positively correlated with baseline GMV in right parahippocampal and orbitofrontal gyri in DwO. Successful dieters showed greater GMV loss in the left precentral gyrus and the insula compared with unsuccessful dieters. A negative correlation was found between %WL and GMV change from baseline in the left prefrontal regions.

CONCLUSIONS

Findings illustrate that WL is related to volumetric changes in brain areas previously linked to interoception and food motivation.

The Effect of Depo Medroxyprogesterone Acetate (DMPA) on Cerebral Food Motivation Centers: A Pilot Study using Functional Magnetic Resonance Imaging

OBJECTIVE

The primary objective is to examine activation of food motivation centers in the brain before and 8 weeks after depo medroxyprogesterone acetate (DMPA) administration.

STUDY DESIGN

This prospective experimental pilot study examined the effects of DMPA on food motivation centers utilizing functional magnetic resonance imaging (fMRI) in eight nonobese, ovulatory subjects. fMRI blood oxygen level dependent (BOLD) signal was measured using a 3-Tesla Scanner while participants viewed images of high-calorie foods, low-calorie foods and nonfood objects. fMRI scans were performed at baseline and 8 weeks after participants received one intramuscular dose of DMPA 150 mg. fMRI data were analyzed using the FMRIB Software Library. Changes in adiposity and circulating leptin and ghrelin levels were also measured.

RESULTS

There was a greater BOLD signal response to food cues in brain regions associated with food motivation (anterior cingulate gyrus, orbitofrontal cortex) 8 weeks after DMPA administration compared to baseline (z>2.3, p<.05 whole-brain analysis clustered corrected). No statistically significant change was detected in circulating leptin or ghrelin levels or fat mass 8 weeks after DMPA administration.

CONCLUSION

Analysis of differences in food motivation may guide the development of interventions to prevent weight gain in DMPA users.

IMPLICATIONS

These data support a neural origin as one of the mechanisms underlying weight gain in DMPA users and may guide future research examining weight gain and contraception.

Deep brain stimulation for obesity: rationale and approach to trial design

Obesity is one of the most serious public health concerns in the US. While bariatric surgery has been shown to be successful for treatment of morbid obesity for those who have undergone unsuccessful behavioral modification, its associated risks and rates of relapse are not insignificant. There exists a neurological basis for the binge-like feeding behavior observed in morbid obesity that is believed to be due to dysregulation of the reward circuitry. The authors present a review of the evidence of the neuroanatomical basis for obesity, the potential neural targets for deep brain stimulation (DBS), as well as a rationale for DBS and future trial design. Identification of an appropriate patient population that would most likely benefit from this type of therapy is essential. There are also significant cost and ethical considerations for such a neuromodulatory intervention designed to alter maladaptive behavior. Finally, the authors present a consolidated set of inclusion criteria and study end points that should serve as the basis for any trial of DBS for obesity.

Neurobiological features of binge eating disorder

Biobehavioral features associated with binge-eating disorder (BED) have been investigated; however, few systematic reviews to date have described neuroimaging findings from studies of BED. Emerging functional and structural studies support BED as having unique and overlapping neural features as compared with other disorders. Neuroimaging studies provide evidence linking heightened responses to palatable food cues with prefrontal areas, particularly the orbitofrontal cortex (OFC), with specific relationships to hunger and reward-sensitivity measures. While few studies to date have investigated non-food-cue responses; these suggest a generalized hypofunctioning in frontostriatal areas during reward and inhibitory control processes. Early studies applying neuroimaging to treatment efforts suggest that targeting neural function underlying motivational processes may prove important in the treatment of BED.

Prospective associations of eating behaviors with weight gain in infants

OBJECTIVE

To examine whether maternal reports of infant eating behaviors are stable over time and whether eating behaviors are prospectively associated with weight gain.

METHODS

In an ongoing study of infant growth, weight and length were measured at 2 weeks, 3 months, and 5 months of age. Food responsiveness (FR), satiety responsiveness (SR), enjoyment of feeding (EF), and slow eating (SE) were assessed with the Baby Eating Behavior Questionnaire. Repeated measures ANOVA was used to examine changes in eating behaviors from 2 weeks to 5 months. Simple Pearson correlations examined associations among eating behaviors across time and associations of eating behaviors with subsequent change in weight-for-length z-scores.

RESULTS

Among 31 infants studied from 2 weeks to 3 months, FR and SR remained consistent (P < 0.05), and among 21 infants studied from 3 to 5 months, FR, EF, and SE were consistent (P < 0.01). Infants ate more quickly (P < 0.01) and tended to have greater SR with age (P = 0.09). Only SE at 3 months was associated with subsequent gain in weight-for-length (P < 0.05).

CONCLUSIONS

Consistent with previous research, SE was predictive of weight gain during infancy. Given that eating behaviors were largely consistent after 3 months of age, it may be important to encourage the development of healthy eating behaviors during early infancy.

Brain function predictors and outcome of weight loss and weight loss maintenance

Obesity rates are associated with public health consequences and rising health care costs. Weight loss interventions, while effective, do not work for everyone, and weight regain is a significant problem. Eating behavior is influenced by a convergence of processes in the brain, including homeostatic factors and motivational processing that are important contributors to overeating. Initial neuroimaging studies have identified brain regions that respond differently to visual food cues in obese and healthy weight individuals that are positively correlated with reports of hunger in obese participants. While these findings provide mechanisms of overeating, many important questions remain. It is not known whether brain activation patterns change after weight loss, or if they change differentially based on amount of weight lost. Also, little is understood regarding biological processes that contribute to long-term weight maintenance. This study will use neuroimaging in participants while viewing food and non-food images. Functional Magnetic Resonance Imaging will take place before and after completion of a twelve-week weight loss intervention. Obese participants will be followed though a 6-month maintenance period. The study will address three aims: 1. Characterize brain activation underlying food motivation and impulsive behaviors in obese individuals. 2. Identify brain activation changes and predictors of weight loss. 3. Identify brain activation predictors of weight loss maintenance. Findings from this study will have implications for understanding mechanisms of obesity, weight loss, and weight maintenance. Results will be significant to public health and could lead to a better understanding of how differences in brain activation relate to obesity.

Increased brain response to appetitive tastes in the insula and amygdala in obese compared with healthy weight children when sated

Objective

There is evidence of altered neural taste response in female adolescents who are obese, and in adolescents who are at risk for obesity. To further understand risk factors for the development of overeating and obesity, we investigated response to tastes of sucrose and water in 23 obese and healthy weight children.

Methods and design

Thirteen healthy weight (HW) and 10 obese (OB) 8–12 year old children underwent functional magnetic resonance imaging while tasting sucrose and water. Additionally, children completed an eating in the absence of hunger paradigm and a sucrose liking task.

Results

A region of interest analysis revealed an elevated BOLD response to taste (sucrose and water) within the bilateral insula and amygdala in OB children relative to HW children. Whole brain analyses revealed a group by condition interaction within the paracingulate, medial frontal, middle frontal gyri, and right amygdala: post hoc analyses suggested an increased response to sucrose for OB relative to HW children, whereas HW children responded more strongly to water relative to sucrose. In addition, OB children, relative to HW, tended to recruit the right putamen as well as medial and lateral frontal and temporal regions bilaterally.

Conclusion

This study showed increased reactivity in the amygdala and insula in the OB compared to HW children, but no functional differentiation in the striatum, despite differences in the striatum previously seen in older samples. These findings support the concept of the association between increased neural processing of food reward in the development of obesity, and raise the possibility that emotional and interoceptive sensitivity could be an early vulnerability in obesity.

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.

Obesity-associated melanocortin-4 receptor mutations are associated with changes in the brain response to food cues

CONTEXT

Mutations in the melanocortin-4 receptor (MC4R) represent the commonest genetic form of obesity and are associated with hyperphagia.

OBJECTIVE

The aim of this study was to investigate whether melanocortin signaling modulates anticipatory food reward by studying the brain activation response to food cues in individuals with MC4R mutations. Design/Setting/Participants/Main Outcome Measure: We used functional magnetic resonance imaging to measure blood oxygen level-dependent responses to images of highly palatable, appetizing foods, bland foods, and non-food objects in eight obese individuals with MC4R mutations, 10 equally obese controls, and eight lean controls with normal MC4R genotypes. Based on previous evidence, we performed a region-of-interest analysis centered on the caudate/putamen (dorsal striatum) and ventral striatum.

RESULTS

Compared to non-foods, appetizing foods were associated with activation in the dorsal and ventral striatum in lean controls and in MC4R-deficient individuals. Surprisingly, we observed reduced activation of the dorsal and ventral striatum in obese controls relative to MC4R-deficient patients and lean controls. There were no group differences for the contrast of disgusting foods with bland foods or non-foods, suggesting that the effects observed in response to appetizing foods were not related to arousal.

CONCLUSION

We identified differences in the striatal response to food cues between two groups of obese individuals, those with and those without MC4R mutations. These findings are consistent with a role for central melanocortinergic circuits in the neural response to visual food cues.

Response to deep brain stimulation in the lateral hypothalamic area in a rat model of obesity: in vivo assessment of brain glucose metabolism

PURPOSE

To investigate changes in glucose brain metabolism after deep brain stimulation (DBS) in the lateral hypothalamic area (LHA) in a rat model of obesity.

PROCEDURES

Ten obese male Zucker rats were divided into two groups: LHA-control and LHA-DBS. Concentric bipolar platinum-iridium electrodes were implanted bilaterally. After 7 days, DBS was applied for 15 days. Weight and food and water intake were monitored. 2-Deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) PET-CT imaging studies were performed the day after the end of DBS. Differences in glucose uptake between the groups were assessed with statistical parametric mapping.

RESULTS

A difference in weight gain of 3.19 percentage points was found between groups. Average food consumption during the first 15 days was lower in DBS-treated animals than in non-stimulated animals. DBS increased metabolism in the mammillary body, subiculum-hippocampal area, and amygdala, while a decrease in metabolism was recorded in the thalamus, caudate, temporal cortex, and cerebellum.

CONCLUSIONS

DBS produced significant changes in brain regions associated with the control of food intake and the brain reward system. DBS seems to normalize the impaired hippocampal functioning that has been described in obese rats. The smaller weight gain in the DBS group suggests that this technique could be considered an option for the treatment of obesity.

Differential reward response to palatable food cues in past and current dieters: a fMRI study

OBJECTIVE

Prior neuroimaging research has shown that restrained and unrestrained eaters demonstrate differential brain activation in response to food cues that parallels their food intake in lab studies. These findings were extended by comparing brain activation in response to food cues in normal weight nondieters, historical dieters, and current dieters under the conditions that mimicked past lab studies.

METHODS

Participants (N = 30) were shown pictures of highly and moderately palatable food and neutral cues while being scanned in an fMRI BOLD paradigm following an 8-h fast and again after a liquid meal.

RESULTS

In the Fed state, historical dieters showed elevated reward circuitry activation in response to highly palatable food, as compared to nondieters and current dieters. In contrast, current dieters did not show the same pattern of activation as historical dieters, despite their shared history of frequent weight-loss dieting.

CONCLUSIONS

The parallels between eating behavior and regional brain activation across groups suggest that (1) a neurophysiological response which could represent a vulnerability to overeat exists in some normal weight young women that may increase susceptibility to weight gain in the long term, and (2) current dieting temporarily reverses this vulnerability.

Neuromodulation for eating disorders: obesity and anorexia

Extremes of eating disorders (ED) have become prevalent in both developed and developing countries. Available therapies, though largely effective, fail in a substantial number of patients and carry considerable side effects. Morbid obesity and anorexia nervosa (AN) represent important causes of morbidity and mortality among young adults. Morbid obesity affects disproportionate numbers of children. AN is also important for its high mortality in young adults. The challenges of effectively treating AN are well recognized. In this article, important aspects of ED are reviewed in detail and novel approaches to the treatment of ED are proposed.

Regional cerebral blood flow and abnormal eating behavior in Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is a genetically determined neurodevelopmental disorder and is generally regarded as a genetic model of obesity. Individuals with PWS exhibit behavioral symptoms including temper tantrums, rigid thinking, and compulsive behavior. The most striking feature of PWS is abnormal eating behavior, including hyperphagia, intense preoccupation with food, and incessant food seeking. To explore brain regions associated with the behavioral symptoms of PWS, we investigated differences in resting-state regional cerebral blood flow (rCBF) between individuals with PWS and healthy controls. Correlation analyses were also performed to examine the relationship between rCBF and altered eating behavior in PWS individuals.

METHODS

Twelve adults with PWS and 13 age- and gender-matched controls underwent resting-state single photon emission computerized tomography (SPECT) with N-isopropyl-p-[(123)I] iodoamphetamine (IMP). The rCBF data were analyzed on a voxel-by-voxel basis using SPM5 software.

RESULTS

The results demonstrated that compared with controls, individuals with PWS had significantly lower rCBF in the right thalamus, left insular cortex, bilateral lingual gyrus, and bilateral cerebellum. They had significantly higher rCBF in the right inferior frontal gyrus, left middle/inferior frontal gyrus (anterior and posterior clusters), and bilateral angular gyrus. Additionally, rCBF in the left insula, which was significantly lower in PWS individuals, was negatively correlated with the eating behavior severity score.

CONCLUSIONS

These results suggest that specific brain regions, particularly the left insula, may be partly responsible for the behavioral symptoms in PWS.

Neural correlates of stress- and food cue-induced food craving in obesity: association with insulin levels

OBJECTIVE

Obesity is associated with alterations in corticolimbic-striatal brain regions involved in food motivation and reward. Stress and the presence of food cues may each motivate eating and engage corticolimibic-striatal neurocircuitry. It is unknown how these factors interact to influence brain responses and whether these interactions are influenced by obesity, insulin levels, and insulin sensitivity. We hypothesized that obese individuals would show greater responses in corticolimbic-striatal neurocircuitry after exposure to stress and food cues and that brain activations would correlate with subjective food craving, insulin levels, and HOMA-IR.

RESEARCH DESIGN AND METHODS

Fasting insulin levels were assessed in obese and lean subjects who were exposed to individualized stress and favorite-food cues during functional MRI.

RESULTS

Obese, but not lean, individuals exhibited increased activation in striatal, insular, and hypothalamic regions during exposure to favorite-food and stress cues. In obese but not lean individuals, food craving, insulin, and HOMA-IR levels correlated positively with neural activity in corticolimbic-striatal brain regions during favorite-food and stress cues. The relationship between insulin resistance and food craving in obese individuals was mediated by activity in motivation-reward regions including the striatum, insula, and thalamus.

CONCLUSIONS

These findings demonstrate that obese, but not lean, individuals exhibit increased corticolimbic-striatal activation in response to favorite-food and stress cues and that these brain responses mediate the relationship between HOMA-IR and food craving. Improving insulin sensitivity and in turn reducing corticolimbic-striatal reactivity to food cues and stress may diminish food craving and affect eating behavior in obesity.

The relationship between executive function and obesity in children and adolescents: a systematic literature review

The objective of this paper is to examine the relationship between the development of executive function (EF) and obesity in children and adolescents. We reviewed 1,065 unique abstracts: 31 from PubMed, 87 from Google Scholar, 16 from Science Direct, and 931 from PsycINFO. Of those abstracts, 28 met inclusion criteria and were reviewed. From the articles reviewed, an additional 3 articles were added from article references (N = 31). Twenty-three studies pertained to EF (2 also studied the prefrontal and orbitofrontal cortices (OFCs); 6 also studied cognitive function), five studied the relationship between obesity and prefrontal and orbitofrontal cortices, and three evaluated cognitive function and obesity. Inhibitory control was most often studied in both childhood (76.9%) and adolescent (72.7%) studies, and obese children performed significantly worse (P < 0.05) than healthy weight controls on various tasks measuring this EF domain. Although 27.3% of adolescent studies measured mental flexibility, no childhood studies examined this EF domain. Adolescents with higher BMI had a strong association with neurostructural deficits evident in the OFC. Future research should be longitudinal and use a uniform method of EF measurement to better establish causality between EF and obesity and consequently direct future intervention strategies.

Disfunção hipotalâmica na obesidade

A obesidade, definida como o acúmulo excessivo ou anormal de gordura que pode causar dano à saúde do indivíduo, é considerada atualmente um dos principais problemas de saúde pública. Resulta de um desequilíbrio entre a ingestão alimentar e o gasto corporal de energia. O controle do balanço energético de animais e seres humanos é realizado pelo sistema nervoso central (SNC) por meio de conexões neuroendócrinas, em que hormônios periféricos circulantes, como a leptina e a insulina, sinalizam neurônios especializados do hipotálamo sobre os estoques de gordura do organismo e induzem respostas apropriadas para a manutenção da estabilidade desses estoques. A maioria dos casos de obesidade se associa a um quadro de resistência central à ação da leptina e da insulina. Em animais de experimentação, a dieta hiperlipídica é capaz de induzir um processo inflamatório no hipotálamo, que interfere com as vias intracelulares de sinalização por esses hormônios, resultando em hiperfagia, diminuição do gasto de energia e, por fim, obesidade. Evidências recentes obtidas por intermédio de estudos de neuroimagem e avaliação de marcadores inflamatórios no líquido cefalorraquidiano de indivíduos obesos sugerem que alterações semelhantes podem estar presentes também em seres humanos. Nesta revisão, apresentamos sumariamente os mecanismos envolvidos com a perda do controle homeostático do balanço energético em modelos animais de obesidade e as evidências atuais de disfunção hipotalâmica em humanos obesos.

Aerobic exercise reduces neuronal responses in food reward brain regions

Acute exercise suppresses ad libitum energy intake, but little is known about the effects of exercise on food reward brain regions. After an overnight fast, 30 (17 men, 13 women), healthy, habitually active (age = 22.2 ± 0.7 yr, body mass index = 23.6 ± 0.4 kg/m(2), Vo(2peak) = 44.2 ± 1.5 ml·kg(-1)·min(-1)) individuals completed 60 min of exercise on a cycle ergometer or 60 min of rest (no-exercise) in a counterbalanced, crossover fashion. After each condition, blood oxygen level-dependent responses to high-energy food, low-energy food, and control visual cues, were measured by functional magnetic resonance imaging. Exercise, compared with no-exercise, significantly (P < 0.005) reduced the neuronal response to food (high and low food) cues vs. control cues in the insula (-0.37 ± 0.13 vs. +0.07 ± 0.18%), putamen (-0.39 ± 0.10 vs. -0.10 ± 0.09%), and rolandic operculum (-0.37 ± 0.17 vs. 0.17 ± 0.12%). Exercise alone significantly (P < 0.005) reduced the neuronal response to high food vs. control and low food vs. control cues in the inferior orbitofrontal cortex (-0.94 ± 0.33%), insula (-0.37 ± 0.13%), and putamen (-0.41 ± 0.10%). No-exercise alone significantly (P < 0.005) reduced the neuronal response to high vs. control and low vs. control cues in the middle (-0.47 ± 0.15%) and inferior occipital gyrus (-1.00 ± 0.23%). Exercise reduced neuronal responses in brain regions consistent with reduced pleasure of food, reduced incentive motivation to eat, and reduced anticipation and consumption of food. Reduced neuronal response in these food reward brain regions after exercise is in line with the paradigm that acute exercise suppresses subsequent energy intake.

Expanding applications of deep brain stimulation: a potential therapeutic role in obesity and addiction management

BACKGROUND

The indications for deep brain stimulation (DBS) are expanding, and the feasibility and efficacy of this surgical procedure in various neurologic and neuropsychiatric disorders continue to be tested. This review attempts to provide background and rationale for applying this therapeutic option to obesity and addiction. We review neural targets currently under clinical investigation for DBS—the hypothalamus and nucleus accumbens—in conditions such as cluster headache and obsessive-compulsive disorder. These brain regions have also been strongly implicated in obesity and addiction. These disorders are frequently refractory, with very high rates of weight regain or relapse, respectively, despite the best available treatments.

METHODS

We performed a structured literature review of the animal studies of DBS, which revealed attenuation of food intake, increased metabolism, or decreased drug seeking. We also review the available radiologic evidence in humans, implicating the hypothalamus and nucleus in obesity and addiction.

RESULTS

The available evidence of the promise of DBS in these conditions combined with significant medical need, support pursuing pilot studies and clinical trials of DBS in order to decrease the risk of dietary and drug relapse.

CONCLUSIONS

Well-designed pilot studies and clinical trials enrolling carefully selected patients with obesity or addiction should be initiated.

Relation of regional gray and white matter volumes to current BMI and future increases in BMI: a prospective MRI study

OBJECTIVE

This study tested whether global and regional brain volumes correlated with body mass index (BMI) and increases in BMI over 1-year follow-up.

METHODS

A total of 83 young females (M age=18.4, s.d.=2.8; BMI range=17.3-38.9) were scanned using magnetic resonance imaging. Voxel-based morphometry was used to assess global brain volume and regional gray matter (GM) and white matter (WM) volumes in regions implicated in taste, reward and inhibitory control.

RESULTS

Obese participants had less total GM volume than lean and overweight participants. Obese participants had lower total WM volume than overweight participants. BMI correlated with higher WM volumes in the middle temporal gyrus, fusiform gyrus, parahippocampal gyrus, Rolandic operculum and dorsal striatum. Trend-level reduced GM volumes in the superior frontal gyrus and middle frontal gyrus were related to increases in BMI over 1-year follow-up.

CONCLUSION

Findings suggest that BMI is related to global and regional differences in brain matter volume in female adolescents. Most importantly, findings suggest that low GM volume in regions implicated in inhibitory control are related to future weight gain. Results taken in conjunction with prior findings suggest that abnormalities in regional GM volumes, but not WM volumes, increase the risk for future weight gain and abnormalities in regional WM volumes, but not GM volumes, are secondary to weight gain.

Resting state cortical electroencephalographic rhythms in subjects with normal and abnormal body weight

It is well known that resting state regional cerebral blood flow is abnormal in obese when compared to normal-weight subjects but the underlying neurophysiological mechanisms are poorly known. To address this issue, we tested the hypothesis that amplitude of resting state cortical electroencephalographic (EEG) rhythms differ among underweight, normal-weight, and overweight/obese subjects as a reflection of the relationship between cortical neural synchronization and regulation of body weight. Eyes-closed resting state EEG data were recorded in 16 underweight subjects, 25 normal-weight subjects, and 18 overweight/obese subjects. All subjects were psychophysically healthy (no eating disorders or major psychopathologies). EEG rhythms of interest were delta (2-4Hz), theta (4-8Hz), alpha 1 (8-10.5Hz), alpha 2 (10.5-13Hz), beta 1 (13-20Hz), beta 2 (20-30Hz), and gamma (30-40Hz). EEG cortical sources were estimated by low-resolution brain electromagnetic tomography (LORETA). Statistical results showed that parietal and temporal alpha 1 sources fitted the pattern underweight>normal-weight>overweight/obese (p<0.004), whereas occipital alpha 1 sources fitted the pattern normal-weight>underweight>overweight/obese (p<0.00003). Furthermore, amplitude of the parietal, occipital, and temporal alpha 2 sources was stronger in the normal-weight subjects than in the underweight and overweight/obese subjects (p<0.0007). These results suggest that abnormal weight in healthy overweight/obese subjects is related to abnormal cortical neural synchronization at the basis of resting state alpha rhythms and fluctuation of global brain arousal.

Prefrontal systems involvement in binge eating

OBJECTIVE

This study examined whether severity of binge eating is associated with dysfunction in behaviors mediated by the three main areas of the prefrontal cortex (PFC).

METHODS

One hundred fifty-one adults (mean BMI=49.50) were classified into three groups based on the presence and severity of binge eating behaviors: Binge Eating Disorder (BED) group (N=22), Binge Eating Prone (BEP) group (N=47), and non-Eating Disorder (non-ED) group (N=82). Participants completed the Frontal Systems Behavior Scale (FrSBe), a widely used measure of neurobehavioral traits associated with the three primary regions of the PFC corresponding with the behavioral traits of apathy, disinhibition, and executive dysfunction.

RESULTS

The BED and BEP groups scored significantly higher than the non-ED group on the three FrSBe subscales, as well as the FrSBe Total score. There were no significant correlations between the FrSBe and participant BMI.

DISCUSSION

As expected, individuals who engaged in binge eating endorsed greater PFC dysfunction than those who did not binge eat. These results provide a complement to studies utilizing neuroimaging and neuropsychological methodologies and further support for the role of prefrontal systems in the regulation of eating behavior.

Molecular annotation of integrative feeding neural circuits

The identity of higher-order neurons and circuits playing an associative role to control feeding is unknown. We injected pseudorabies virus, a retrograde tracer, into masseter muscle, salivary gland, and tongue of BAC-transgenic mice expressing GFP in specific neural populations and identified several CNS regions that project multisynaptically to the periphery. MCH and orexin neurons were identified in the lateral hypothalamus, and Nurr1 and Cnr1 in the amygdala and insular/rhinal cortices. Cholera toxin β tracing showed that insular Nurr1(+) and Cnr1(+) neurons project to the amygdala or lateral hypothalamus, respectively. Finally, we show that cortical Cnr1(+) neurons show increased Cnr1 mRNA and c-Fos expression after fasting, consistent with a possible role for Cnr1(+) neurons in feeding. Overall, these studies define a general approach for identifying specific molecular markers for neurons in complex neural circuits. These markers now provide a means for functional studies of specific neuronal populations in feeding or other complex behaviors.

Peptide hormones regulating appetite--focus on neuroimaging studies in humans

In recent years, knowledge about hormonal feedback from the gastrointestinal tract and adipose tissue has increased tremendously. Peptide hormones modulating hunger have been intensively studied, mostly in animals but increasingly also in humans. The first therapeutic agents, such as GLP-1 analogues, are in successful clinical use for T2D and may beneficially affect hunger and reduce weight. Data from in vitro studies and animals provide detailed insight into regulatory mechanisms leading to peptide secretion and receptor bindings, as well as to the distribution of receptors involved in different parts of the body. With neuroimaging techniques human brain structures have been identified that play a role in hunger, satiety and eating behaviour. These include the primary gustatory (insular) and olfactory (pyriform) cortex and regions with a highly permeable blood-brain barrier (hypothalamus, brain stem), which facilitates humoral input via gut peptides and leptin. In addition, cerebral networks involved in higher cognitive functions, especially those relevant to reward, pleasure and also addiction (ventral and dorsal striatum, amygdala, orbitofrontal cortex (OFC), prefrontal cortex (PFC)) were shown to be involved. First indications of direct influences of peptide hormones on these networks have become available from neuroimaging studies administrating synthetic PYY, ghrelin and leptin. Insulin also appears to play an important role as a central satiety hormone, and evidence indicating the possibility of central insulin resistance in obesity is available.

Mood disorders and obesity: understanding inflammation as a pathophysiological nexus

The aim of this review is to evaluate the evidentiary base supporting the hypothesis that the increased hazard for obesity in mood disorder populations (and vice versa) is a consequence of shared pathophysiological pathways. We conducted a PubMed search of all English-language articles with the following search terms: obesity, inflammation, hypothalamic-pituitary-adrenal axis, insulin, cognition, CNS, and neurotransmitters, cross-referenced with major depressive disorder and bipolar disorder. The frequent co-occurrence of mood disorders and obesity may be characterized by interconnected pathophysiology. Both conditions are marked by structural and functional abnormalities in multiple cortical and subcortical brain regions that subserve cognitive and/or affective processing. Abnormalities in several interacting biological networks (e.g. immuno-inflammatory, insulin signaling, and counterregulatory hormones) contribute to the co-occurence of mood disorders and obesity. Unequivocal evidence now indicates that obesity and mood disorders are chronic low-grade pro-inflammatory states that result in a gradual accumulation of allostatic load. Abnormalities in key effector proteins of the pro-inflammatory cascade include, but are not limited to, cytokines/adipokines such as adiponectin, leptin, and resistin as well as tumor necrosis factor alpha and interleukin-6. Taken together, the bidirectional relationship between obesity and mood disorders may represent an exophenotypic manifestation of aberrant neural and inflammatory networks. The clinical implications of these observations are that, practitioners should screen individuals with obesity for the presence of clinically significant depressive symptoms (and vice versa). This clinical recommendation is amplified in individuals presenting with biochemical indicators of insulin resistance and other concurrent conditions associated with abnormal inflammatory signaling (e.g. cardiovascular disease).

Food addiction and obesity: evidence from bench to bedside

Obesity has become a major health problem and epidemic. However, much of the current debate has been fractious and etiologies of obesity have been attributed to eating behavior or fast food, personality issues, depression, addiction, or genetics. One of the interesting new hypotheses for epidemic obesity is food addiction, which is associated with both substance-related disorder and eating disorder. Accumulating evidences have shown that there are many shared neural and hormonal pathways as well as distinct differences that may help researchers find why certain individuals overeat and become obese. Functional neuroimaging studies have further revealed that good or great smelling, looking, tasting, and reinforcing food has characteristics similar to that of drugs of abuse. Many of the brain changes reported for hedonic eating and obesity are also seen in various forms of addictions. Most importantly, overeating and obesity may have an acquired drive like drug addiction with respect to motivation and incentive; craving, wanting, and liking occur after early and repeated exposures to stimuli. The acquired drive for great food and relative weakness of the satiety signal would cause an imbalance between the drive and hunger/reward centers in the brain and their regulation.