Working memory and reward association learning impairments in obesity

Contrasting frontal cortical responses to food versus money rewards across BMI groups

Previous research has linked obesity with an altered perception of rewards. This study aimed to contrast frontal cortical activities across body mass index (BMI) groups, in responding to differential rewards (monetary versus food). A total of 60 male participants (27.43 ± 6.07 years of age; 21 normal weight [BMI: 18.5-24.9 kg·m-2]; 20 overweight [BMI: 25.0-29.9 kg·m-2]; and 19 individuals with obesity [BMI ≥ 30 kg·m-2]) were tested for their response bias towards food and money rewards using the Probabilistic Reward Task (PRT), while their frontal cortical responses were recorded using electroencephalography (EEG). The feedback-related negativity (FRN), a reliable measure of reward valuation and learning, was calculated for food (FRN(Food)) and money (FRN(Money)). Results indicate a left-lateralised frontal cortical activity associated with the food reward condition, in the group of overweight and obesity. In contrast, a right-lateralisation was observed in the money reward condition only in the group with obesity. More specifically, FRN(Food) was shown to significantly differ between left and right frontal cortical areas among individuals with obesity (p = 0.035) and overweight (p = 0.012), but not in normal-weight individuals (p = 0.153). Additionally, results revealed that FRN(Food) and FRN(Money) were significantly different for individuals with obesity (p = 0.019), but such a significant difference was not evident in the overweight and normal-weight individuals (p ≥ 0.05). These findings offer intriguing new insights into neuropsychological differentiation across BMI groups, adding to the understanding of obesity-related behaviour.

Practical strategies to manage obesity in type 2 diabetes

The rising phenomenon of obesity, a major risk factor for the development and progression of type 2 diabetes, is a complex and multifaceted issue that requires a comprehensive and coordinated approach to be prevented and managed. Although novel pharmacological measures to combat obesity have achieved unprecedented efficacy, a healthy lifestyle remains essential for the long-term success of any therapeutic intervention. However, this requires a high level of intrinsic motivation and continued behavioural changes in the face of multiple metabolic, psychological and environmental factors promoting weight gain, particularly in the context of type 2 diabetes. This review is intended to provide practical recommendations in the context of a holistic, person-centred approach to weight management, including evidence-based and expert recommendations addressing supportive communication, shared decision-making, as well as nutritional and pharmacological therapeutic approaches to achieve sustained weight loss.

LRP1 in GABAergic neurons is a key link between obesity and memory function

OBJECTIVE

Low-density lipoprotein receptor-related protein-1 (LRP1) regulates energy homeostasis, blood-brain barrier integrity, and metabolic signaling in the brain. Deficiency of LRP1 in inhibitory gamma-aminobutyric acid (GABA)ergic neurons causes severe obesity in mice. However, the impact of LRP1 in inhibitory neurons on memory function and cognition in the context of obesity is poorly understood.

METHODS

Mice lacking LRP1 in GABAergic neurons (Vgat-Cre; LRP1loxP/loxP) underwent behavioral tests for locomotor activity and motor coordination, short/long-term and spatial memory, and fear learning/memory. This study evaluated the relationships between behavior and metabolic risk factors and followed the mice at 16 and 32 weeks of age.

RESULTS

Deletion of LRP1 in GABAergic neurons caused a significant impairment in memory function in 32-week-old mice. In the spatial Y-maze test, Vgat-Cre; LRP1loxP/loxP mice exhibited decreased travel distance and duration in the novel arm compared with controls (LRP1loxP/loxP mice). In addition, GABAergic neuron-specific LRP1-deficient mice showed a diminished capacity for performing learning and memory tasks during the water T-maze test. Moreover, reduced freezing time was observed in these mice during the contextual and cued fear conditioning tests. These effects were accompanied by increased neuronal necrosis and satellitosis in the hippocampus. Importantly, the distance and duration in the novel arm, as well as the performance of the reversal water T-maze test, negatively correlated with metabolic risk parameters, including body weight, serum leptin, insulin, and apolipoprotein J. However, in 16-week-old Vgat-Cre; LRP1loxP/loxP mice, there were no differences in the behavioral tests or correlations between metabolic parameters and cognition.

CONCLUSIONS

Our findings demonstrate that LRP1 from GABAergic neurons is important in regulating normal learning and memory. Metabolically, obesity caused by GABAergic LRP1 deletion negatively regulates memory and cognitive function in an age-dependent manner. Thus, LRP1 in GABAergic neurons may play a crucial role in maintaining normal excitatory/inhibitory balance, impacting memory function, and reinforcing the potential importance of LRP1 in neural system integrity.

Electrophysiological Characteristics of Inhibitive Control for Adults with Different Physiological or Psychological Obesity

Individuals exhibiting high scores on the fatness subscale of the negative-physical-self scale (NPSS-F) are characterized by heightened preoccupation with body fat accompanied by negative body image perceptions, often leading to excessive dieting behaviors. This demographic constitutes a considerable segment of the populace in China, even among those who are not obese. Nonetheless, scant empirical inquiries have delved into the behavioral and neurophysiological profiles of individuals possessing a healthy body mass index (BMI) alongside elevated NPSS-F scores. This study employed an experimental paradigm integrating go/no-go and one-back tasks to assess inhibitory control and working memory capacities concerning food-related stimuli across three adult cohorts: those with normal weight and low NPSS-F scores, those with normal weight and high NPSS-F scores, and individuals classified as obese. Experimental stimuli comprised high- and low-caloric-food pictures with concurrent electroencephalogram (EEG) and photoplethysmogram (PPG) recordings. Individuals characterized by high NPSS-F scores and normal weight exhibited distinctive electrophysiological responses compared to the other two cohorts, evident in event-related potential (ERP) components, theta and alpha band oscillations, and heart rate variability (HRV) patterns. In essence, the findings underscore alterations in electrophysiological reactivity among individuals possessing high NPSS-F scores and a healthy BMI in the context of food-related stimuli, underscoring the necessity for increased attention to this demographic alongside individuals affected by obesity.

Working memory gating in obesity: Insights from a case-control fMRI study

Computational models and neurophysiological data propose that a 'gating mechanism' coordinates distractor-resistant maintenance and flexible updating of working memory contents: While maintenance of information is mainly implemented in the prefrontal cortex, updating of information is signaled by phasic increases in dopamine in the striatum. Previous literature demonstrates structural and functional alterations in these brain areas, as well as differential dopamine transmission among individuals with obesity, suggesting potential impairments in these processes. To test this hypothesis, we conducted an observational case-control fMRI study, dividing participants into groups with and without obesity based on their BMI. We probed maintenance and updating of working memory contents using a modified delayed match to sample task and investigated the effects of SNPs related to the dopaminergic system. While the task elicited the anticipated brain responses, our findings revealed no evidence for group differences in these two processes, neither at the neural level nor behaviorally. However, depending on Taq1A genotype, which affects dopamine receptor density in the striatum, participants with obesity performed worse on the task. In conclusion, this study does not support the existence of overall obesity-related differences in working memory gating. Instead, we propose that potentially subtle alterations may manifest specifically in individuals with a 'vulnerable' genotype.

Early-life cumulative exposure to excess bodyweight and midlife cognitive function: longitudinal analysis in three British birth cohorts

BACKGROUND

Excess bodyweight (BMI >25 kg/m2) in midlife (age 40-65 years) has been linked to future cognitive decline and an increased risk of dementia. Whether chronic exposure to excess bodyweight in the early decades of life (<40 years) is associated with compromised cognitive function by midlife, however, remains unclear. This study therefore aimed to test potential bidirectional direct and indirect pathways linking cumulative exposure to excess bodyweight and cognitive function in the early decades of life.

METHODS

In this longitudinal analysis, harmonised measures of BMI and cognitive function were available in 19 742 participants aged 47-53 years recruited to the 1946 National Survey of Health and Development (n=2131), the 1958 National Child Development Study (n=9385), and the 1970 British Cohort Study (n=8226). Individual BMI trajectories spanning three decades from age 10-40 years were created for each participant and excess bodyweight duration, BMI change between ages, and cumulative excess bodyweight exposure were calculated. Harmonised measures of verbal and non-verbal ability, mathematical ability, and reading ability were used to create a latent factor for childhood cognitive function, and immediate and delayed recall, animal naming, and letter-search speed tests were used for midlife cognitive function. Multivariable linear regression and structural equation models (SEM) were used to test for potential bidirectional relationships between cognition and excess bodyweight in both individual cohorts and pooled datasets while accounting for other potential early-life confounders.

FINDINGS

Increases in BMI during adolescence and greater cumulative exposure to excess bodyweight across early life were associated with lower midlife cognitive function in all cohorts (eg, pooled difference in cognitive function per 10 years excess bodyweight duration -0·10; 95% CI -0·12 to -0·08; p<0·001). Further adjustment for childhood cognitive function attenuated many of these associations towards the null (eg, pooled difference in cognitive function per 10 years excess bodyweight duration -0·04; 95% CI -0·06 to -0·02; p=0·001), however, with any remaining associations then fully attenuating once further adjusted for other early-life factors (eg, pooled difference in cognitive function per 10 years excess bodyweight duration 0, -0·03 to 0·01; p=0·38). In the reverse direction, low childhood cognition was associated with greater cumulative exposure to excess bodyweight over the next four decades, although much of this relationship was found to probably be explained via other potentially modifiable upstream early-life factors such as childhood disadvantage. SEM in all cohorts suggested the presence of modest direct and indirect pathways connecting earlier cognitive function to later excess bodyweight, but scarce evidence for an effect of early-life excess bodyweight on cognitive function by midlife.

INTERPRETATION

The association between cumulative exposure to excess bodyweight in early life and lower cognitive function in midlife is probably confounded by a persistently lower cognitive function from childhood. Initiatives to improve early-life factors such as childhood disadvantage and education, however, might exert dual but independent benefits on both of these factors before old age.

FUNDING

Alzheimer's Research UK, Diabetes Research and Wellness Foundation, Diabetes UK, British Heart Foundation, and Medical Research Council.

A narrative review about cognitive impairment in metabolic Dysfunction-Associated liver disease (MASLD): Another matter to face through a holistic approach

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic hepatic disorder worldwide in both adults and children. It is well established that MASLD represents the hepatic manifestation of the metabolic syndrome whose definition includes the presence of obesity, type 2 diabetes (T2D), dyslipidemia, hypertension and hypercoagulability. All these conditions contribute to a chronic inflammatory status which may impact on blood brain barrier (BBB) integrity leading to an impaired function of central nervous system (CNS).

AIM OF REVIEW

Since the mechanisms underlying the brain-liver-gut axis derangement are still inconclusive, the present narrative review aims to make a roundup of the most recent studies regarding the cognitive decline in MASLD also highlighting possible therapeutic strategies to reach a holistic advantage for the patients.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Due to its ever-growing prevalence, the MASLD-related mental dysfunction represents an enormous socio-economic burden since it largely impacts on the quality of life of patients as well as on their working productivity. Indeed, cognitive decline in MASLD translates in low concentration and processing speed, reduced memory, sleepiness but also anxiety and depression. Chronic systemic inflammation, hyperammonemia, genetic background and intestinal dysbiosis possibly contribute to the cognitive decline in MASLD patients. However, its diagnosis is still underestimated since the leading mechanisms are multi-faceted and unexplained and do not exist standardized diagnostic tools or cognitive test strategies. In this scenario, nutritional and lifestyle interventions as well as intestinal microbiota manipulation (probiotics, fecal transplantation) may represent new approaches to counteract mental impairment in these subjects. In sum, to face the "mental aspect" of this multifactorial disease which is almost unexplored, cognitive tools should be introduced in the management of MASLD patients.

Long-Term Brain Structure and Cognition Following Bariatric Surgery

Importance

Weight loss induced by bariatric surgery (BS) is associated with improved cognition and changed brain structure; however, previous studies on the association have used small cohorts and short follow-up periods, making it difficult to determine long-term neurological outcomes associated with BS.

Objective

To investigate long-term associations of weight loss after BS with cognition and brain structure and perfusion.

Design, Setting, and Participants

This cohort study included participants from the Bariatric Surgery Rijnstate and Radboudumc Neuroimaging and Cognition in Obesity study. Data from participants with severe obesity (body mass index [BMI; calculated as weight in kilograms divided by height in meters squared] >40, or BMI >35 with comorbidities) eligible for Roux-en-Y gastric bypass and aged 35 to 55 years were enrolled from a hospital specialized in BS (Rijnstate Hospital, Arnhem, the Netherlands). Participants were recruited between September 2018 and December 2020 with follow-up till March 2023. Data were collected before BS and at 6 and 24 months after BS. Data were analyzed from March to November 2023.

Exposure

Roux-en-Y gastric bypass.

Main Outcomes and Measures

Primary outcomes included body weight, BMI, waist circumference, blood pressure, medication use, cognitive performance (20% change index of compound z-score), brain volumes, cortical thickness, cerebral blood flow (CBF), and spatial coefficient of variation (sCOV). Secondary outcomes include cytokines, adipokines, depressive symptoms (assessed using the Beck Depression Inventory), and physical activity (assessed using the Baecke Questionnaire).

Results

A total of 133 participants (mean [SD] age, 46.8 [5.7] years; 112 [84.2%] female) were included. Global cognition was at least 20% higher in 52 participants (42.9%) at 24 months after BS. Compared with baseline, at 24 months, inflammatory markers were lower (mean [SD] high-sensitivity C-reactive protein: 4.77 [5.80] μg/mL vs 0.80 [1.09] μg/mL; P < .001), fewer patients used antihypertensives (48 patients [36.1%] vs 22 patients [16.7%]), and patients had lower depressive symptoms (median [IQR] BDI score: 9.0 [5.0-13.0] vs 3.0 [1.0-6.0]; P < .001) and greater physical activity (mean [SD] Baecke score: 7.64 [1.29] vs 8.19 [1.35]; P < .001). After BS, brain structure and perfusion were lower in most brain regions, while hippocampal and white matter volume remained stable. CBF and sCOV did not change in nucleus accumbens and parietal cortex. The temporal cortex showed a greater thickness (mean [SD] thickness: 2.724 [0.101] mm vs 2.761 [0.007] mm; P = .007) and lower sCOV (median [IQR] sCOV: 4.41% [3.83%-5.18%] vs 3.97% [3.71%-4.59%]; P = .02) after BS.

Conclusions and Relevance

These findings suggest that BS was associated with health benefits 2 years after surgery. BS was associated with improved cognition and general health and changed blood vessel efficiency and cortical thickness of the temporal cortex. These results may improve treatment options for patients with obesity and dementia.

How are overweight and obesity associated with reinforcement learning deficits? A systematic review

Reinforcement learning (RL) refers to the ability to learn stimulus-response or response-outcome associations relevant to the acquisition of behavioral repertoire and adaptation to the environment. Research data from correlational and case-control studies have shown that obesity is associated with impairments in RL. The aim of the present study was to systematically review how obesity and overweight are associated with RL performance. More specifically, the relationship between high body mass index (BMI) and task performance was explored through the analysis of specific RL processes associated with different physiological, computational, and behavioral manifestations. Our systematic analyses indicate that obesity might be associated with impairments in the use of aversive outcomes to change ongoing behavior, as revealed by results involving instrumental negative reinforcement and extinction/reversal learning, but further research needs to be conducted to confirm this association. Hypotheses regarding how obesity might be associated with altered RL were discussed.

Inflammatory Pathways in Overweight and Obese Persons as a Potential Mechanism for Cognitive Impairment and Earlier Onset Alzeihmer's Dementia in the General Population: A Narrative Review

The overweight status or obesity can be confirmed through classical methods such as the body mass index (BMI) and the waist-to-hip ratio (WHR). Apart from metabolic issues such as atherosclerosis, liver steatosis, or diabetes mellitus, long-term obesity or overweight status can pose a risk for cardiovascular and neurovascular complications. While some acute adverse events like coronary syndromes of strokes are well-documented to be linked to an increased body mass, there are also chronic processes that, due to their silent onset and evolution, are underdiagnosed and not as thoroughly studied. Through this review, we aimed to collect all relevant data with regard to the long-term impact of obesity on cognitive function in all ages and its correlation with an earlier onset of dementia such as Alzheimer's disease (AD). The exact mechanisms through which a decline in cognitive functions occurs in overweight or obese persons are still being discussed. A combination of factors has been acknowledged as potential triggers, such as a sedentary lifestyle and stress, as well as a genetic predisposition, for example, the apolipoprotein E (ApoE) alleles in AD. Most research highlights the impact of vascular dysfunction and systemic inflammation on the nervous system in patients with obesity and the subsequent neurological changes. Obesity during the early to mid-ages leads to an earlier onset of cognitive dysfunction in various forms. Also, lifestyle intervention can reverse cognitive dysfunction, especially dieting, to encourage weight loss.

Central mechanisms in sympathetic nervous dysregulation in obesity

Cardiovascular and metabolic complications associated with excess adiposity are linked to chronic activation of the sympathetic nervous system, resulting in a high risk of mortality among obese individuals. Obesity-related positive energy balance underlies the progression of hypertension, end-organ damage, and insulin resistance, driven by increased sympathetic tone throughout the body. It is, therefore, important to understand the central network that drives and maintains sustained activation of the sympathetic nervous system in the obese state. Experimental and clinical studies have identified structural changes and altered dynamics in both grey and white matter regions in obesity. Aberrant activation in certain brain regions has been associated with altered reward circuitry and metabolic pathways including leptin and insulin signaling along with adiposity-driven systemic and central inflammation. The impact of these pathways on the brain via overactivity of the sympathetic nervous system has gained interest in the past decade. Primarily, the brainstem, hypothalamus, amygdala, hippocampus, and cortical structures including the insular, orbitofrontal, temporal, cingulate, and prefrontal cortices have been identified in this context. Although the central network involving these structures is much more intricate, this review highlights recent evidence identifying these regions in sympathetic overactivity in obesity.

The cerebellum plays more than one role in the dysregulation of appetite: Review of structural evidence from typical and eating disorder populations

OBJECTIVE

Dysregulated appetite control is characteristic of anorexia nervosa (AN), bulimia nervosa (BN), and obesity (OB). Studies using a broad range of methods suggest the cerebellum plays an important role in aspects of weight and appetite control, and is implicated in both AN and OB by reports of aberrant gray matter volume (GMV) compared to nonclinical populations. As functions of the cerebellum are anatomically segregated, specific localization of aberrant anatomy may indicate the mechanisms of its relationship with weight and appetite in different states. We sought to determine if there were consistencies in regions of cerebellar GMV changes in AN/BN and OB, as well as across normative (NOR) variation.

METHOD

Systematic review and meta-analysis using GingerALE.

RESULTS

Twenty-six publications were identified as either case-control studies (nOB  = 277; nAN/BN  = 510) or regressed weight from NOR data against brain volume (total n = 3830). AN/BN and OB analyses both showed consistently decreased GMV within Crus I and Lobule VI, but volume reduction was bilateral for AN/BN and unilateral for OB. Analysis of the NOR data set identified a cluster in right posterior lobe that overlapped with AN/BN cerebellar reduction. Sensitivity analyses indicated robust repeatability for NOR and AN/BN cohorts, but found OB-specific heterogeneity.

DISCUSSION

Findings suggest that more than one area of the cerebellum is involved in control of eating behavior and may be differentially affected in normal variation and pathological conditions. Specifically, we hypothesize an association with sensorimotor and emotional learning via Lobule VI in AN/BN, and executive function via Crus I in OB.

Presurgical microstructural coherence predicts cognitive change for bariatric surgery patients

OBJECTIVE

This observational study examined the relationship between presurgical white matter microstructural coherence and cognitive change after weight loss. It was hypothesized that higher baseline fractional anisotropy (FA) would predict greater baseline and change cognition.

METHODS

A sample of 24 adults (BMI ≥ 35 kg/m2 ) underwent neuropsychological assessment at baseline and 12 weeks after bariatric surgery. A magnetic resonance imaging brain scan was administered at baseline and processed through Tract-Based Spatial Statistics to compute FA in white matter tracts of interest. Composite scores for attention, learning, processing speed, executive function, verbal fluency, working memory, and overall cognition were calculated.

RESULTS

As expected, FA in some tracts of interest was significantly (p < 0.05) positively associated with change in cognition. Inverse relationships were observed between baseline FA and presurgical cognition, which may be explained by increased medial and radial diffusivity and preserved axonal diffusivity. Cognition generally improved after surgery; however, relative but clinically nonsignificant deterioration was observed on learning measures. Poorer baseline cognitive performance was associated with greater postsurgical cognitive improvement.

CONCLUSIONS

Presurgical microstructural coherence is associated with magnitude of cognitive change after weight loss. An observed reduction in learning suggests that bariatric surgery may lead to negative outcomes in some cognitive domains, at least temporarily.

The Addiction-Susceptibility TaqIA/Ankk1 Controls Reward and Metabolism Through D2 Receptor-Expressing Neurons

BACKGROUND

A large body of evidence highlights the importance of genetic variants in the development of psychiatric and metabolic conditions. Among these, the TaqIA polymorphism is one of the most commonly studied in psychiatry. TaqIA is located in the gene that codes for the ankyrin repeat and kinase domain containing 1 kinase (Ankk1) near the dopamine D2 receptor (D2R) gene. Homozygous expression of the A1 allele correlates with a 30% to 40% reduction of striatal D2R, a typical feature of addiction, overeating, and other psychiatric pathologies. The mechanisms by which the variant influences dopamine signaling and behavior are unknown.

METHODS

Here, we used transgenic and viral-mediated strategies to reveal the role of Ankk1 in the regulation of activity and functions of the striatum.

RESULTS

We found that Ankk1 is preferentially enriched in striatal D2R-expressing neurons and that Ankk1 loss of function in the dorsal and ventral striatum leads to alteration in learning, impulsivity, and flexibility resembling endophenotypes described in A1 carriers. We also observed an unsuspected role of Ankk1 in striatal D2R-expressing neurons of the ventral striatum in the regulation of energy homeostasis and documented differential nutrient partitioning in humans with or without the A1 allele.

CONCLUSIONS

Overall, our data demonstrate that the Ankk1 gene is necessary for the integrity of striatal functions and reveal a new role for Ankk1 in the regulation of body metabolism.

Reliability of gamified reinforcement learning in densely sampled longitudinal assessments

Reinforcement learning is a core facet of motivation and alterations have been associated with various mental disorders. To build better models of individual learning, repeated measurement of value-based decision-making is crucial. However, the focus on lab-based assessment of reward learning has limited the number of measurements and the test-retest reliability of many decision-related parameters is therefore unknown. In this paper, we present an open-source cross-platform application Influenca that provides a novel reward learning task complemented by ecological momentary assessment (EMA) of current mental and physiological states for repeated assessment over weeks. In this task, players have to identify the most effective medication by integrating reward values with changing probabilities to win (according to random Gaussian walks). Participants can complete up to 31 runs with 150 trials each. To encourage replay, in-game screens provide feedback on the progress. Using an initial validation sample of 384 players (9729 runs), we found that reinforcement learning parameters such as the learning rate and reward sensitivity show poor to fair intra-class correlations (ICC: 0.22-0.53), indicating substantial within- and between-subject variance. Notably, items assessing the psychological state showed comparable ICCs as reinforcement learning parameters. To conclude, our innovative and openly customizable app framework provides a gamified task that optimizes repeated assessments of reward learning to better quantify intra- and inter-individual differences in value-based decision-making over time.

Habitual intake of fat and sugar is associated with poorer memory and greater impulsivity in humans

The vicious cycle model of obesity suggests that repeated habitual intake of a diet high in fat and sugar (HFS) results in impairment in hippocampal function which in turn increases impulsive behaviours, making it harder to resist unhealthy diet choices. Evidence from studies with rodents consistently show switching to a HFS diet impairs performance on hippocampally-sensitive memory tasks. The limited literature in humans also suggest impaired memory and increased impulsivity related to higher habitual HFS intake. However, these changes in memory and impulsivity have been looked at independently. To investigate how these effects are inter-related, three experiments were conducted where relative HFS intake was related to measures of memory and impulsivity. In Experiment 1 (90 female participants), HFS was associated with higher scores on the Everyday Memory Questionnaire-revised (EMQ), and higher scores on the total, Attention (BISatt) and Motor (BISmot) sub-scales of the Barratt Impulsiveness Scale (BIS11). Experiment 2 (84 women and 35 men), replicated the association between HFS and EMQ, and also found HFS related to poorer performance on the hippocampally-sensitive 4 mountain (4MT) memory task. The association between HFS intake and the BISatt replicated, but there were no significant associations with other BIS11 measures or delay-discounting for monetary rewards. Experiment 3 (199 women and 87 men) replicated the associations between DFS and 4MT and EMQ, and also found an association with overall recall, but not response inhibition, from a Remembering Causes Forgetting task: HFS was also significantly associated with BIS total, BISatt and BISmot. In all three studies these associations remained when potential confounds (BMI, age, gender, hunger state, restrained and disinhibited eating) were controlled for. Mediation analysis found that the effect of HFS on memory at least part mediated the relationship between HFS and impulsivity in Experiments 1 and 3, but not 2. Overall these data provide some support for the vicious cycle model, but also suggest that trait impulsivity may be a risk factor for poor dietary choice.

Liraglutide restores impaired associative learning in individuals with obesity

Survival under selective pressure is driven by the ability of our brain to use sensory information to our advantage to control physiological needs. To that end, neural circuits receive and integrate external environmental cues and internal metabolic signals to form learned sensory associations, consequently motivating and adapting our behaviour. The dopaminergic midbrain plays a crucial role in learning adaptive behaviour and is particularly sensitive to peripheral metabolic signals, including intestinal peptides, such as glucagon-like peptide 1 (GLP-1). In a single-blinded, randomized, controlled, crossover basic human functional magnetic resonance imaging study relying on a computational model of the adaptive learning process underlying behavioural responses, we show that adaptive learning is reduced when metabolic sensing is impaired in obesity, as indexed by reduced insulin sensitivity (participants: N = 30 with normal insulin sensitivity; N = 24 with impaired insulin sensitivity). Treatment with the GLP-1 receptor agonist liraglutide normalizes impaired learning of sensory associations in men and women with obesity. Collectively, our findings reveal that GLP-1 receptor activation modulates associative learning in people with obesity via its central effects within the mesoaccumbens pathway. These findings provide evidence for how metabolic signals can act as neuromodulators to adapt our behaviour to our body's internal state and how GLP-1 receptor agonists work in clinics.

Food reinforcement architecture: A framework for impulsive and compulsive overeating and food abuse

Few reward-based theories address key drivers of susceptibility to food cues and consumption beyond fullness. Decision-making and habit formation are governed by reinforcement-based learning processes that, when overstimulated, can drive unregulated hedonically motivated overeating. Here, a model food reinforcement architecture is proposed that uses fundamental concepts in reinforcement and decision-making to identify maladaptive eating habits that can lead to obesity. This model is unique in that it identifies metabolic drivers of reward and incorporates neuroscience, computational decision-making, and psychology to map overeating and obesity. Food reinforcement architecture identifies two paths to overeating: a propensity for hedonic targeting of food cues contributing to impulsive overeating and lack of satiation that contributes to compulsive overeating. A combination of those paths will result in a conscious and subconscious drive to overeat independent of negative consequences, leading to food abuse and/or obesity. Use of this model to identify aberrant reinforcement learning processes and decision-making systems that can serve as markers of overeating risk may provide an opportunity for early intervention in obesity.

The association between regional adiposity, cognitive function, and dementia-related brain changes: a systematic review

Background

Adiposity has been previously associated with cognitive impairment and Alzheimer's disease and related disorders (ADRD). Body mass index (BMI) is the most common measure of global adiposity, but inconsistent results were found since it is a global measurement. BMI does not represent regional fat distribution which differs between sexes, race, and age. Regional fat distribution may contribute differently to cognitive decline and Alzheimer's disease (AD)-related brain changes. Fat-specific targeted therapies could lead to personalized improvement of cognition. The goal of this systematic review is to explore whether regional fat depots, rather than central obesity, should be used to understand the mechanism underlying the association between adiposity and brain.

Methods

This systematic review included 33 studies in the English language, conducted in humans aged 18 years and over with assessment of regional adiposity, cognitive function, dementia, and brain measures. We included only studies that have assessed regional adiposity using imaging technics and excluded studies that were review articles, abstract only or letters to editor. Studies on children and adolescents, animal studies, and studies of patients with gastrointestinal diseases were excluded. PubMed, PsychInfo and web of science were used as electronic databases for literature search until November 2022.

Results

Based on the currently available literature, the findings suggest that different regional fat depots are likely associated with increased risk of cognitive impairment, brain changes and dementia, especially AD. However, different regional fat depots can have different cognitive outcomes and affect the brain differently. Visceral adipose tissue (VAT) was the most studied regional fat, along with liver fat through non-alcoholic fatty liver disease (NAFLD). Pancreatic fat was the least studied regional fat.

Conclusion

Regional adiposity, which is modifiable, may explain discrepancies in associations of global adiposity, brain, and cognition. Specific regional fat depots lead to abnormal secretion of adipose factors which in turn may penetrate the blood brain barrier leading to brain damage and to cognitive decline.

Distinct adaptations of endocrine and cognitive functions may contribute to high variability in long-term weight loss outcome after bariatric surgery

BACKGROUND

Bariatric surgery has been widely recognized as the most efficient long-term treatment method in severe obesity, yet therapy success shows considerable interindividual variability. Postoperative metabolic adaptations, including improved gut hormone secretion (GLP-1, PYY and ghrelin), and restored executive function may play an explanatory role in weight loss, yet causes for poor success in individual patients remain unknown. This study investigates gut-hormonal and cognitive characteristics in extreme weight loss responders to bariatric surgery.

METHODS

Patients (n=47) with high or low excessive weight loss (EWL) at least 2 years after Roux-en-Y-gastric bypass or sleeve gastrectomy were allocated into good responders (GR, EWL 82.4 ± 11.6%) and poor responders (PR, EWL 24.0 ± SD 12.8%) to study differences in postprandial secretion of GLP-1, PYY, ghrelin and in working memory (WM).

RESULTS

Mean BMI was 47.1 ± 6.2 kg/m² in PR (n=21) and 28.9 ± 3.1 kg/m² in GR (n=26, p < 0.001). Fasted GLP-1 and PYY were comparable for GR and PR (p > 0.2) and increased strongly after a standardized test meal (300 kcal liquid meal) with a peak at 15 to 30 minutes. The increase was stronger in GR compared to PR (GLP-1, PYY: Time x Group p < 0.05). Plasma ghrelin levels already differed between groups at fasted state, showing significantly higher levels for GR (p < 0.05). Postprandially, ghrelin secretion was suppressed in both groups, but suppression was higher in GR (Time x Group p < 0.05). GR showed significantly higher WM scores than PR (p < 0.05). Postprandial ghrelin (iAUC), but not GLP-1 or PYY plasma levels, significantly mediated the relationship between EWL and a WM subscore (IS score, CI = 0.07 - 1.68), but not WM main score (MIS score, CI = -0.07 - 1.54), in mediation analyses.

CONCLUSION

Excess weight loss success after bariatric surgical procedures is associated with distinct profiles of gut-hormones at fasted and postprandial state, and differences in working memory. Better working memory performance in GR might be mediated by higher postprandial reduction in ghrelin plasma levels. Future studies need to integrate longitudinal data, larger samples and more sensitive cognitive tests.

Matrix disequilibrium in Alzheimer's disease and conditions that increase Alzheimer's disease risk

Alzheimer's Disease (AD) and related dementias are a leading cause of death globally and are predicted to increase in prevalence. Despite this expected increase in the prevalence of AD, we have yet to elucidate the causality of the neurodegeneration observed in AD and we lack effective therapeutics to combat the progressive neuronal loss. Throughout the past 30 years, several non-mutually exclusive hypotheses have arisen to explain the causative pathologies in AD: amyloid cascade, hyper-phosphorylated tau accumulation, cholinergic loss, chronic neuroinflammation, oxidative stress, and mitochondrial and cerebrovascular dysfunction. Published studies in this field have also focused on changes in neuronal extracellular matrix (ECM), which is critical to synaptic formation, function, and stability. Two of the greatest non-modifiable risk factors for development of AD (aside from autosomal dominant familial AD gene mutations) are aging and APOE status, and two of the greatest modifiable risk factors for AD and related dementias are untreated major depressive disorder (MDD) and obesity. Indeed, the risk of developing AD doubles for every 5 years after ≥ 65, and the APOE4 allele increases AD risk with the greatest risk in homozygous APOE4 carriers. In this review, we will describe mechanisms by which excess ECM accumulation may contribute to AD pathology and discuss pathological ECM alterations that occur in AD as well as conditions that increase the AD risk. We will discuss the relationship of AD risk factors to chronic central nervous system and peripheral inflammation and detail ECM changes that may follow. In addition, we will discuss recent data our lab has obtained on ECM components and effectors in APOE4/4 and APOE3/3 expressing murine brain lysates, as well as human cerebrospinal fluid (CSF) samples from APOE3 and APOE4 expressing AD individuals. We will describe the principal molecules that function in ECM turnover as well as abnormalities in these molecular systems that have been observed in AD. Finally, we will communicate therapeutic interventions that have the potential to modulate ECM deposition and turnover in vivo.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.

Impact of insulin and insulin resistance on brain dopamine signalling and reward processing- an underexplored mechanism in the pathophysiology of depression?

Type 2 diabetes and major depressive disorder (MDD) are the leading causes of disability worldwide and have a high comorbidity rate with fatal outcomes. Despite the long-established association between these conditions, the underlying molecular mechanisms remain unknown. Since the discovery of insulin receptors in the brain and the brain's reward system, evidence has accumulated indicating that insulin modulates dopaminergic (DA) signalling and reward behaviour. Here, we review the evidence from rodent and human studies, that insulin resistance directly alters central DA pathways, which may result in motivational deficits and depressive symptoms. Specifically, we first elaborate on the differential effects of insulin on DA signalling in the ventral tegmental area (VTA) - the primary DA source region in the midbrain - and the striatum as well as its effects on behaviour. We then focus on the alterations induced by insulin deficiency and resistance. Finally, we review the impact of insulin resistance in DA pathways in promoting depressive symptoms and anhedonia on a molecular and epidemiological level and discuss its relevance for stratified treatment strategies.

Self-reported intake of high-fat and high-sugar diet is not associated with cognitive stability and flexibility in healthy men

Animal studies indicate that a high-fat/high-sugar diet (HFS) can change dopamine signal transmission in the brain, which could promote maladaptive behavior and decision-making. Such diet-induced changes may also explain observed alterations in the dopamine system in human obesity. Genetic variants that modulate dopamine transmission have been proposed to render some individuals more prone to potential effects of HFS. The objective of this study was to investigate the association of HFS with dopamine-dependent cognition in humans and how genetic variations might modulate this potential association. Using a questionnaire assessing the self-reported consumption of high-fat/high-sugar foods, we investigated the association with diet by recruiting healthy young men that fall into the lower or upper end of that questionnaire (low fat/sugar group: LFS, n = 45; high fat/sugar group: HFS, n = 41) and explored the interaction of fat and sugar consumption with COMT Val¹⁵⁸Met and Taq1A genotype. During functional magnetic resonance imaging (fMRI) scanning, male participants performed a working memory (WM) task that probes distractor-resistance and updating of WM representations. Logistic and linear regression models revealed no significant difference in WM performance between the two diet groups, nor an interaction with COMT Val¹⁵⁸Met or Taq1A genotype. Neural activation in task-related brain areas also did not differ between diet groups. Independent of diet group, higher BMI was associated with lower overall accuracy on the WM task. This cross-sectional study does not provide evidence for diet-related differences in WM stability and flexibility in men, nor for a predisposition of COMT Val¹⁵⁸Met or Taq1A genotype to the hypothesized detrimental effects of an HFS diet. Previously reported associations of BMI with WM seem to be independent of HFS intake in our male study sample.

Food memory circuits regulate eating and energy balance

In mammals, learning circuits play an essential role in energy balance by creating associations between sensory cues and the rewarding qualities of food. This process is altered by diet-induced obesity, but the causes and mechanisms are poorly understood. Here, we exploited the relative simplicity and wealth of knowledge about the D. melanogaster reinforcement learning network, the mushroom body, in order to study the relationship between the dietary environment, dopamine-induced plasticity, and food associations. We show flies that are fed a high-sugar diet cannot make associations between sensory cues and the rewarding properties of sugar. This deficit was caused by diet exposure, not fat accumulation, and specifically by lower dopamine-induced plasticity onto mushroom body output neurons (MBONs) during learning. Importantly, food memories dynamically tune the output of MBONs during eating, which instead remains fixed in sugar-diet animals. Interestingly, manipulating the activity of MBONs influenced eating and fat mass, depending on the diet. Altogether, this work advances our fundamental understanding of the mechanisms, causes, and consequences of the dietary environment on reinforcement learning and ingestive behavior.

Poor Cognitive Agility Conservation in Obese Aging People

Life expectancy has been boosted in recent decades at expenses of increasing the age-associated diseases. Dementia, for its incidence, stands out among the pathologies associated with aging. The exacerbated cognitive deterioration disables people from carrying out their daily lives autonomously and this incidence increases exponentially after 65 years of age. The etiology of dementia is a miscellaneous combination of risk factors that restrain the quality of life of our elderly. In this sense, it has been established that some metabolic pathologies such as obesity and diabetes act as a risk factor for dementia development. In contrast, a high educational level, as well as moderate physical activity, have been shown to be protective factors against cognitive impairment and the development of dementia. In the present study, we have evaluated the metabolic composition of a population between 60-90 years old, mentally healthy and with high academic degrees. After assessing agility in mental state, we have established relationships between their cognitive abilities and their body composition. Our data support that excess body fat is associated with poorer maintenance of cognition, while higher percentages of muscle mass are associated with the best results in the cognitive tests.

The relationship between sleep and appetitive conditioning: A systematic review and meta-analysis

This systematic review and meta-analysis (PROSPERO registration animal/human studies: CRD42021234793/CRD42021234790) examined the relationship between sleep and appetitive conditioning. Inclusion criteria included: a) appetitive conditioning paradigm; b) measure of conditioning; c) sleep measurement and/or sleep loss; d) human and/etor non-human animal samples; and e) written in English. Searches of seven databases returned 3777 publications. The final sample consisted of 42 studies using primarily animal samples and involving food- and drug-related conditioning tasks. We found sleep loss disrupted appetitive conditioning of food rewards (p < 0.001) but potentiated appetitive conditioning of drug rewards (p < 0.001). Furthermore, sleep loss negatively impacted extinction learning irrespective of the reward type. Post-learning sleep was associated with increases in REM sleep (p = 0.02). Findings suggest sleep loss potentiates the impact of psychoactive substances in a manner likely to produce an increased risk of problematic substance use. In obese/overweight populations, sleep loss may be associated with deficits in the conditioning and extinction of reward-related behaviours. Further research should assess the relationship between sleep and appetitive conditioning in humans.

Obesity Is Associated With Gait Alterations and Gait Asymmetry in Older Adults

OBJECTIVES

The prevalence of obesity (OB) has increased in the older adult (OA) population. However, it is not quite clear whether OB exaggerates gait instability and leads to a higher risk of falls in OAs. The first goal of this study was to investigate whether OB is associated with gait alterations and gait asymmetry in OAs. The second goal of this study was to examine relationships between various OB measures with gait measures and gait symmetry measures in OAs.

METHODS

A total of 30 OAs were included and categorized according to their body mass index (BMI) values into groups of persons with normal weight (NW), overweight (OW), and OB. Participants were required to complete an anthropometric assessment, a body composition assessment, and overground walking tests.

RESULTS

The group with OB had shorter swing phase, longer stance phase, and shorter single support phase than the NW group. Increased body weight, BMI, visceral adipose tissue mass, and android fat had correlations with shorter swing phase, longer stance phase, and shorter single support phase. Increased body weight and BMI had significantly positive correlations with symmetry index of knee range of motion.

CONCLUSIONS

OB may impair gait automation capacity in OAs. Both body weight and BMI remain good measures in terms of establishing correlations with gait stability in OAs. However, the amount of fat mass surrounding the abdomen could be vital to interpreting the alterations in the gait of OAs with obesity.

Reduced brain activity during a working memory task in middle-aged apolipoprotein E ε4 carriers with overweight/obesity

Objective

The apolipoprotein E ε4 (APOE ε4) allele and midlife obesity are independent risk factors for Alzheimer's disease (AD). Both of these risk factors are also associated with differences in brain activation, as measured by blood oxygenation level-dependent (BOLD) responses, in the absence of detectable cognitive deficits. Although the presence of these risk factors may influence brain activity during working memory tasks, no study to date has examined whether the presence of the ε4 allele explains variation in working memory brain activity while matching for levels of overweight/obesity. The primary aim of this study was to determine whether the presence of the ε4 allele is associated with differences in task-functional magnetic resonance imaging (fMRI) brain activation in adults with overweight/obesity. We predicted that ε4 carriers would have greater brain activation in regions that support working memory.

Methods

This ancillary study included 48 (n = 24 APOE ε4 carriers; n = 24 APOE ε4 non-carriers), sedentary middle-aged adults (Mean age = 44.63 ± 8.36 years) with overweight/obesity (Mean BMI = 32.43 ± 4.12 kg/m²) who were matched on demographic characteristics. Participants were a subsample enrolled in 12-month randomized clinical trial examining the impact of energy-restricted diet and exercise on cardiovascular health outcomes. Participants completed a n-back working memory task with fMRI, which were completed within one month of the start of the intervention. Participants also underwent pseudo-continuous arterial spin labeling scans, a MRI measure of cerebral blood flow (CBF).

Results

Compared to non-ε4 carriers with overweight/obesity, ε4 carriers with overweight/obesity had lower fMRI brain activity in the middle frontal gyrus, pre and post central gyrus, supramarginal gyrus, superior temporal gyrus, lateral occipital cortex, and angular gyrus (z range = 2.52-3.56) during the n-back working memory task. Differences persisted even when controlling for CBF in these brain regions.

Conclusion

These results indicate that presence of the APOE ε4 allele in middle-aged adults with overweight/obesity is related to altered brain activity during a working memory paradigm, which may confer risk for accelerated neurocognitive decline in late adulthood. Future research is needed to clarify the clinical implications of these findings in the context of risk for AD.

Feeding the Brain: Effect of Nutrients on Cognition, Synaptic Function, and AMPA Receptors

In recent decades, traditional eating habits have been replaced by a more globalized diet, rich in saturated fatty acids and simple sugars. Extensive evidence shows that these dietary factors contribute to cognitive health impairment as well as increase the incidence of metabolic diseases such as obesity and diabetes. However, how these nutrients modulate synaptic function and neuroplasticity is poorly understood. We review the Western, ketogenic, and paleolithic diets for their effects on cognition and correlations with synaptic changes, focusing mainly (but not exclusively) on animal model studies aimed at tracing molecular alterations that may contribute to impaired human cognition. We observe that memory and learning deficits mediated by high-fat/high-sugar diets, even over short exposure times, are associated with reduced arborization, widened synaptic cleft, narrowed post-synaptic zone, and decreased activity-dependent synaptic plasticity in the hippocampus, and also observe that these alterations correlate with deregulation of the AMPA-type glutamate ionotropic receptors (AMPARs) that are crucial to neuroplasticity. Furthermore, we explored which diet-mediated mechanisms modulate synaptic AMPARs and whether certain supplements or nutritional interventions could reverse deleterious effects, contributing to improved learning and memory in older people and patients with Alzheimer’s disease.

Working memory development from early childhood to adolescence using two nationally representative samples

We leveraged nationally representative data from the Panel study of Income Dynamics-Child Development Supplement (N = 3,562) and the Early Childhood Longitudinal study (N = 18,174), to chart the development of working memory, indexed via verbal forward and backward digit span task performance, from 3 to 19 years of age. Results revealed nonlinear growth patterns for forward and backward digit span tasks, with the most rapid growth occurring during childhood followed by a brief accelerated period of growth during early adolescence. We also found similar developmental trajectories on digit span task performance for males and females across the U.S. population. Together, this study highlights the relative importance of the childhood period for working memory development and provides researchers with a reference against which to compare the developmental changes of working memory in individual studies. From a practical perspective, clinicians and educators can also use this information to understand important periods of working memory growth using national developmental trends. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Overweight and executive functions, psychological and behavioral profile of Spanish adolescents

The prevalence of overweight and obesity among children and adolescents has risen dramatically increasing a major risk factor for non-communicable diseases and cognitive dysfunctions. This study aimed to analyze differences in the executive function´s development between overweight and normal-weight adolescents. As a secondary objective, we aimed to assess differences in adolescents' psychological and behavioral profiles between groups. In order to achieve the study's aim, 105 adolescent students (17.61 ± 7.43 years) completed an online questionnaire that analyzed variables regarding their executive functions' processes, their psychological and physical health as well as lifestyle habits. Results showed that executive functions development is associated with adolescent weight. A higher range of weight presents a lower ability to assess abstract reasoning and to shift cognitive strategies. Nevertheless, no differences were found between groups in the capacity to hold information in mind nor the ability to control impulsive responses. Furthermore, groups showed differences in the number of meals and gastritis, but no significant differences have been found in lifestyle variables such as mobile usage, smoking, physical activity, and hours of sleep per day. The results from the present study could be used to implement multidisciplinary programs to develop healthier habits.

Context Matters: Preliminary Evidence That the Association between Positive Affect and Adiposity in Infancy Varies in Social vs. Non-Social Situations

Previous studies have suggested that infants high in negative affect have higher levels of adiposity, arising in part via changes in nutrition (e.g., “feeding to soothe”). Few studies have examined whether positive affect shows similar or inverse associations with adiposity. The current study examined cross-sectional and longitudinal relationships between adiposity and observations of positive affect in both a social and a non-social context, using data from infants at four (n = 125) and 12 (n = 80) months of age. Our analyses did not find any cross-sectional associations between positive affect and adiposity (all p > 0.05). However, in the longitudinal analyses, positive affect in a non-social context, when observed at four months of age, was positively associated with weight-for-length at 12 months of age (zWFL; ß = 1.49, SE = 0.67, p = 0.03), while positive affect observed at four months of age in a social context was inversely associated with body fat percentage at 12 months of age (ß = −11.41, SE = 5.44, p = 0.04). These findings provide preliminary evidence that the p positive affect is related to adiposity in infancy and suggest that the direction of association (i.e., direct or inverse) may be specific to the context in which positive affect is measured. Future research should examine the role of nutritional status in any relationships between adiposity and emotion at this early stage.

A Neuroeconomics Approach to Obesity

Obesity is a heterogeneous condition that is affected by physiological, behavioral, and environmental factors. Value-based decision making is a useful framework for integrating these factors at the individual level. The disciplines of behavioral economics and reinforcement learning provide tools for identifying specific cognitive and motivational processes that may contribute to the development and maintenance of obesity. Neuroeconomics complements these disciplines by studying the neural mechanisms underlying these processes. We surveyed recent literature on individual decision characteristics that are most frequently implicated in obesity: discounting the value of future outcomes, attitudes toward uncertainty, and learning from rewards and punishments. Our survey highlighted both consistent and inconsistent behavioral findings. These findings underscore the need to examine multiple processes within individuals to identify unique behavioral profiles associated with obesity. Such individual characterization will inform future studies on the neurobiology of obesity as well as the design of effective interventions that are individually tailored.

Correlation between Body Mass Index (BMI) and Performance on the Montreal Cognitive Assessment (MoCA) in a Cohort of Adult Women in South Africa

Objective. Recent evidence suggests that obesity is increasing worldwide and may negatively impact neurocognition. Local studies on the association of weight status with neurocognitive function are sparse. This study is aimed at examining the association between body mass index (BMI) and neurocognitive functioning scores in a cohort of adult women. Methods. A convenience sample of 175 women aged 18 to 59 years ( $28.03\pm 8.87$ ) recruited in a community-based quantitative study completed the Montreal Cognitive Assessment (MoCA). The BMI metric was used to measure body fat based on weight and height and was stratified as high BMI (overweight or obese) or low BMI (normal weight). The Beck Depression Inventory (BDI) was used to assess depression. Pearson’s correlation analysis and the student’s $t$ -test analysis were performed. Results. We observed a significant inverse association between BMI and performance on MoCA ( $r\left(173\right)=-0.32$ , $p<0.001$ ). Performance on subtest of attention, memory, constructive abstraction, and executive functions significantly and inversely correlated with BMI. Significantly lower scores on the MoCA were found in women with a high BMI compared to women with a low BMI ( $23\pm 4$ vs. $26\pm 3$ ), $t\left(173\right)=4.12$ , $p<0.0001$ ). Conclusions. BMI and MoCA were inversely associated on both global and domain-specific neurocognitive test of attention, memory, and executive function; key neurocognitive control; and regulatory functions underlying behavior and decision-making. The findings provide a rationale for further research into the long-term effects of BMI on neurocognition.

Memory and eating: A bidirectional relationship implicated in obesity

This paper reviews evidence demonstrating a bidirectional relationship between memory and eating in humans and rodents. In humans, amnesia is associated with impaired processing of hunger and satiety cues, disrupted memory of recent meals, and overconsumption. In healthy participants, meal-related memory limits subsequent ingestive behavior and obesity is associated with impaired memory and disturbances in the hippocampus. Evidence from rodents suggests that dorsal hippocampal neural activity contributes to the ability of meal-related memory to control future intake, that endocrine and neuropeptide systems act in the ventral hippocampus to provide cues regarding energy status and regulate learned aspects of eating, and that consumption of hypercaloric diets and obesity disrupt these processes. Collectively, this evidence indicates that diet-induced obesity may be caused and/or maintained, at least in part, by a vicious cycle wherein excess intake disrupts hippocampal functioning, which further increases intake. This perspective may advance our understanding of how the brain controls eating, the neural mechanisms that contribute to eating-related disorders, and identify how to treat diet-induced obesity.

Western diet as a trigger of Alzheimer's disease: From metabolic syndrome and systemic inflammation to neuroinflammation and neurodegeneration

An excess of saturated fatty acids and simple sugars in the diet is a known environmental risk factor of Alzheimer's disease (AD) but the holistic view of the interacting processes through which such diet may contribute to AD pathogenesis is missing. We addressed this need through extensive analysis of published studies investigating the effects of western diet (WD) on AD development in humans and laboratory animals. We reviewed WD-induced systemic alterations comprising metabolic changes, induction of obesity and adipose tissue inflammation, gut microbiota dysbiosis and acceleration of systemic low-grade inflammation. Next we provide an overview of the evidence demonstrating that WD-associated systemic alterations drive impairment of the blood-brain barrier (BBB) and development of neuroinflammation paralleled by accumulation of toxic amyloid. Later these changes are followed by dysfunction of synaptic transmission, neurodegeneration and finally memory and cognitive impairment. We conclude that WD can trigger AD by acceleration of inflammaging, and that BBB impairment induced by metabolic and systemic inflammation play the central role in this process. Moreover, the concurrence of neuroinflammation and Aβ dyshomeostasis, which by reciprocal interactions drive the vicious cycle of neurodegeneration, contradicts Aβ as the primary trigger of AD. Given that in 2019 the World Health Organization recommended focusing on modifiable risk factors in AD prevention, this overview of the sequential, complex pathomechanisms initiated by WD, which can lead from peripheral disturbances to neurodegeneration, can support future prevention strategies.

Targeting executive function for weight loss in adults with overweight or obesity

Obesity is associated with a multitude of negative health sequalae. Behavioral weight loss (BWL) is currently the recommended behavioral treatment for obesity; however, it is not effective for approximately half of the individuals who participate. BWL requires individuals to carry out many tasks requiring executive function (EF; i.e., higher order cognitive functions such as planning and problem solving) in order to be successful. Growing research supports that lower EF may be associated with attenuated weight loss following BWL, and targeting EF in treatment could improve outcomes. This paper aims to describe the rationale for the development of Novel Executive Function Training for Obesity (NEXT), which adapts Compensatory Cognitive Training to be delivered in conjunction with BWL. We summarize evidence relating EF to obesity and reduced weight loss following BWL, as well as the past success of cognitive training on EF. Then we describe the treatment model for NEXT followed by initial data suggesting that NEXT is feasible and acceptable and may impact EF and weight. Obesity treatments incorporating cognitive training, especially those that train compensatory strategies, may improve weight-loss outcomes and provide a more durable treatment than traditional interventions, but larger randomized control trials are necessary.

Is the habit system altered in individuals with obesity? A systematic review

Habit-like eating behavior is repeatedly pointed to as a key cognitive mechanism contributing to the emergence and maintenance of obesity. Here, we conducted a systematic review of the literature to assess the existent behavioral evidence for the Habit Hypothesis for Overeating (HHO) which states that obesity is the consequence of an imbalance between the habit and goal-directed reward learning systems, leading to overconsumption of food. We found a total of 19 studies implementing a variety of experimental protocols (i.e., free operant paradigm, slips-of-action test, two-step task, Pavlovian-to-Instrumental paradigm, probabilistic learning task) and manipulations. Taken together, the studies on clinical (binge eating disorder) and non-clinical individuals with overweight or obesity do not support the HHO conclusively. While the scientific literature on HHO is still in its infancy, the heterogeneity of the extant studies makes it difficult to evaluate the degree of convergence of these findings. Uncovering the role of reward learning systems in eating behaviors might have a transformative impact on public health.

Metformin restores hippocampal neurogenesis and learning and memory via regulating gut microbiota in the obese mouse model

Numerous studies have shown that over-nutritional obesity may lead to pre-diabetes, type 2 diabetes and cognitive decline. As the degree of metabolic disorders increases, the cognitive decline is getting worse. However, the cellular events that cause this cognitive dysfunction is yet to be clarified. We used a high-fat diet (HFD) consumption-induced obesity mouse model to test the effects of metformin on the hippocampal neurogenesis and learning and memory abilities of obese mice. 5-Bromo-2'-deoxyuridine (BrdU) labelling and retrovirus labeling were applied to detect hippocampal newborn neurons. Behavioral experiments were used to detect learning and memory abilities of mice. 16S rRNA gene sequencing was performed to detect the composition of gut microbiota. The positron emission tomography (PET) was conducted to detect the energy metabolism activity of different mouse brain regions. Our results reveal that metformin restores the impairment of neurogenesis in the dentate gyrus and finally prevents the cognitive decline of the obese mice. Moreover, the therapeutic effects of metformin are achieved by regulating the composition of gut microbiota of mice, which may inhibit microglia activation and neuroinflammation in the brain of obese mice. This study suggests that metformin may be taken as a promising candidate for the intervention of cognitive decline related to imbalance of gut microbiota caused by obesity.

Metabolic syndrome and cognitive performance across the adult lifespan

Metabolic Syndrome (MetS) is associated with increased rates of mortality and increased risk for developing dementia. Changes in brain structure and cognitive functioning have been reported within the literature. However, research examining cognitive performance in individuals with MetS is limited, inconclusive, and focuses primarily on older cohorts. As such, the effect of MetS on cognitive functioning earlier in the lifespan is unclear. This study aimed to investigate cognitive performance in young, middle-aged, and older adults with multiple metabolic and vascular risk factors in a sample of community dwelling participants (N = 128). Participants were administered a comprehensive neuropsychological battery and self-report measures. As expected, older adults performed more poorly than young and middle-aged adults across most assessments. Relative to controls, individuals with MetS reported greater hunger and disinhibited eating. MetS participants performed more poorly on Color-Word Interference: Inhibition. Additionally, when weight was accounted for, there was a significant relationship between MetS and select executive functioning tasks in middle-aged adults. These findings suggest that aspects of executive functioning may be impaired in MetS and could be further impacted by excess weight in middle-age. Future studies aimed at investigating potential causal relationships between metabolic and vascular risk factors, disinhibited eating, and executive dysfunction may provide insight into effective intervention targets to prevent MetS.

Fat and Carbohydrate Interact to Potentiate Food Reward in Healthy Weight but Not in Overweight or Obesity

Prior work suggests that actual, but not estimated, energy density drives the reinforcing value of food and that energy from fat and carbohydrate can interact to potentiate reward. Here we sought to replicate these findings in an American sample and to determine if the effects are influenced by body mass index (BMI). Thirty participants with healthy weight (HW; BMI 21.92 ± 1.77; M ± SD) and 30 participants with overweight/obesity (OW/OB; BMI 29.42 ± 4.44) rated pictures of common American snacks in 120-kcal portions for liking, familiarity, frequency of consumption, expected satiety, healthiness, energy content, energy density, and price. Participants then completed an auction task where they bid for the opportunity to consume each food. Snacks contained either primarily carbohydrate, primarily fat, or roughly equal portions of fat and carbohydrate (combo). Replicating prior work, we found that participants with HW bid the most for combo foods in linear mixed model analyses. This effect was not observed among individuals with OW/OB. Additionally, in contrast with previous reports, our linear regression analyses revealed a negative relationship between the actual energy density of the snacks and bid amount that was mediated by food price. Our findings support altered macronutrient reinforcement in obesity and highlight potential influences of the food environment on the regulation of food reward.

Executive Functions and Body Weight at Different Ages: A Preliminary Study

Recently, researchers have focused their attention on the role of cognitive processes on eating habits and body weight changes. Few studies have examined the relationship between the first stages of overweight and executive functions (EFs), excluding obesity conditions. This study is aimed to detect the involvement of the EFs and their predictive role on body mass index (BMI) in a sample of healthy individuals from childhood to young adulthood with a cross-sectional design. One-hundred and sixty-six healthy students were recruited from different Italian public schools: 46 children (age range: 7–11), 50 adolescents (age range: 15–18), 70 young adults (age range: 19–30). BMI was used to evaluate body weight and different EFs tasks were used to assess the EFs domains of inhibition, updating and shifting. After adjusting BMI for age, a hierarchical multiple linear regression was carried out for each EFs task. Pearson’s r correlations were reported for each of the age subgroups. Motor disinhibition was associated with greater BMI in the overall sample. Higher BMI was related to poorer set-shifting in adolescence and poorer motor inhibition in young adulthood, but higher BMI was not associated with EFs in childhood. Differences in the development of EFs over time may influence weight changes over time through different responses to food and eating behavior.

Age, BMI, and inflammation: Associations with emotion recognition

Experimental studies show that inflammation impairs the ability to interpret the mental state of another person, denoted theory of mind (ToM). The current study attempted a conceptual replication in states associated with elevated low-grade inflammation, i.e., high body weight and advanced age. Ninety young (M = 26.3 years, SD = 4.1) or older (M = 70.7 years, SD = 4.0) participants with either a normal body mass index (BMI) (M = 22.4, SD = 2.2) or high BMI (M = 33.1, SD = 3.8) completed the Reading the Mind in the Eyes Test (RMET) to assess emotion recognition. Plasma interleukin-6 (IL-6) level was measured to index low-grade inflammation. As anticipated, elevated IL-6 levels were found with higher BMI, although not with increased age. IL-6 was associated with poorer task performance, independent of potential demographic and health confounders (e.g., sex, education, smoking status, alcohol intake, presence of medical conditions, and medication intake). Analyses also revealed an interaction whereby young individuals with a high BMI showed worse RMET performance compared to their normal BMI counterparts, whereas the opposite pattern was found in older individuals. The present observational study replicated experimental results showing that elevated low-grade inflammation is correlated with a lower ability to infer the mental states of others. These findings suggest that also naturalistic conditions of (protracted) low-grade inflammation may alter emotion recognition.

The weight of school grades: Evidence of biased teachers' evaluations against overweight students in Germany

Discrimination and prejudice against overweight people is common in Western societies. In this article we aim to understand whether these attitudes reverberate into the school setting, by investigating whether teachers grade overweight students more severely than comparable normal weight students. By relying on the Attribution-Value Model of Prejudice (AVMP) and previous studies, we test a series of hypotheses using data from the German National Educational Panel Study (NEPS SC3) on a sample of students enrolled in the 7^th grade (lower secondary education). We used hierarchical ordered logit regression to assess whether overweight and obese students receive systematically lower grades by their teachers in German and mathematics, adjusting for subject-specific competences measured with a standardized test, and a rich set of socio-demographic and socio-psychological students’ characteristics (e.g. the “big five”). Results suggested that overweight and obese students were more severely graded in both subjects. The penalty for overweight students, and especially for obese students, was slightly larger in German and in the lowest part of the grade distribution. There was also indication of heterogeneous penalties by gender, with overweight male students being especially penalized in math. Possible ways to help teachers in assigning grades in a fairer way are discussed at the end.

The Neurobiology of Binge-eating Disorder Compared with Obesity: Implications for Differential Therapeutics

PURPOSE

Emerging work indicates divergence in the neurobiologies of binge-eating disorder (BED) and obesity despite their frequent co-occurrence. This review highlights specific distinguishing aspects of BED, including elevated impulsivity and compulsivity possibly involving the mesocorticolimbic dopamine system, and discusses implications for differential therapeutics for BED.

METHODS

This narrative review describes epidemiologic, clinical, genetic, and preclinical differences between BED and obesity. Subsequently, this review discusses human neuroimaging work reporting differences in executive functioning, reward processing, and emotion reactivity in BED compared with obesity. Finally, on the basis of the neurobiology of BED, this review identifies existing and new therapeutic agents that may be most promising given their specific targets based on putative mechanisms of action relevant specifically to BED.

FINDINGS

BED is characterized by elevated impulsivity and compulsivity compared with obesity, which is reflected in divergent neurobiological characteristics and effective pharmacotherapies. Therapeutic agents that influence both reward and executive function systems may be especially effective for BED.

IMPLICATIONS

Greater attention to impulsivity/compulsivity-related, reward-related, and emotion reactivity-related processes may enhance conceptualization and treatment approaches for patients with BED. Consideration of these distinguishing characteristics and processes could have implications for more targeted pharmacologic treatment research and interventions.

Effects of physical activity interventions on cognitive performance of overweight or obese children and adolescents: a systematic review and meta-analysis

BACKGROUND

Physical activity (PA) and obesity were linked with poor cognition. Our study assessed PA interventions could improve domain-specific cognition among overweight/obese youth.

METHODS

Systematically searched PubMed to identify relevant studies published up to October 2019. Standardized mean differences (SMD) of pre-post intervention were calculated in meta-analysis. The level of study heterogeneity represented by I² was interpreted as small (I² ≤ 25%), moderate (25% < I² ≤ 50%), substantial (50% < I² ≤ 75%), or considerable (I² > 75%).

RESULTS

Seventeen studies met the inclusion criteria; eight were included in the meta-analysis. Meta-analysis revealed that PA interventions improved core executive functions (core-EFs) (SMD = 0.301; 95% CI = 0.002-0.600; I²% = 80.6%) and non-EFs (SMD = 0.159; 95% CI = 0.029-0.289; I²% = 0.0%), but not metacognition and academic performance. Core-EFs benefited from enriched PA (SMD = 0.535; 95% CI = 0.020-1.051; I²% = 72.0%) and enhanced and enriched PA (SMD = 1.005; 95% CI = 0.017-1.993; I²% = 90.8%) interventions, while the non-EFs benefited more from enhanced PA (SMD = 0.166; 95% CI = 0.018-0.314; I²% = 0.0%). Interventions with a favorable effect on adiposity measures resulted in a significantly greater improvement in core-EFs (SMD = 0.438; 95% CI = 0.047-0.829; I²% = 58.8%) than those with no effects.

CONCLUSIONS

PA interventions can improve several domains of cognition, especially core-EFs and non-EFs, and the effects are affected by PA characteristics among overweight and obese youth.

IMPACT

Our study is the first to quantify the effect of PA interventions on CP among overweight or obese children and adolescents. Physical activity interventions positively affect cognitive performance, especially core executive functions (core-EFs) and non-EFs. Physical activity interventions seem to not positively affect metacognition (higher-level EFs and cognitive life skills) and academic performance. Physical task characteristics could influence the effect of chronic exercise on cognitive performance. Short-term physical activity programs may be particularly beneficial to affect core-EFs.

Reliance on model-based and model-free control in obesity

Consuming more energy than is expended may reflect a failure of control over eating behaviour in obesity. Behavioural control arises from a balance between two dissociable strategies of reinforcement learning: model-free and model-based. We hypothesized that weight status relates to an imbalance in reliance on model-based and model-free control, and that it may do so in a linear or quadratic manner. To test this, 90 healthy participants in a wide BMI range [normal-weight (n = 31), overweight (n = 29), obese (n = 30)] performed a sequential decision-making task. The primary analysis indicated that obese participants relied less on model-based control than overweight and normal-weight participants, with no difference between overweight and normal-weight participants. In line, secondary continuous analyses revealed a negative linear, but not quadratic, relationship between BMI and model-based control. Computational modelling of choice behaviour suggested that a mixture of both strategies was shifted towards less model-based control in obese participants. Our findings suggest that obesity may indeed be related to an imbalance in behavioural control as expressed in a phenotype of less model-based control potentially resulting from enhanced reliance on model-free computations.

Preliminary evidence for an association between intake of high-fat high-sugar diet, variations in peripheral dopamine precursor availability and dopamine-dependent cognition in humans

Obesity is associated with alterations in dopaminergic transmission and cognitive function. Rodent studies suggest that diets rich in saturated fat and refined sugars (HFS), as opposed to diets diets low in saturated fat and refined sugars (LFS), change the dopamine system independent of excessive body weight. However, the impact of HFS on the human brain has not been investigated. Here, we compared the effect of dietary dopamine depletion on dopamine-dependent cognitive task performance between two groups differing in habitual intake of dietary fat and sugar. Specifically, we used a double-blind within-subject cross-over design to compare the effect of acute phenylalanine/tyrosine depletion on a reinforcement learning and a working memory task, in two groups that are on opposite ends of the spectrum of self-reported HFS intake (low vs high intake: LFS vs HFS group). We tested 31 healthy young women matched for body mass index (mostly normal weight to overweight) and IQ. Depletion of peripheral precursors of dopamine reduced the working memory specific performance on the operation span task in the LFS, but not in the HFS group (P = 0.016). Learning from positive- and negative-reinforcement (probabilistic selection task) was increased in both diet groups after dopamine depletion (P = 0.049). As a secondary exploratory research question, we measured peripheral dopamine precursor availability (pDAP) at baseline as an estimate for central dopamine levels. The HFS group had a significantly higher pDAP at baseline compared to the LFS group (P = 0.025). Our data provide the first evidence indicating that the intake of HFS is associated with changes in dopamine precursor availability, which is suggestive of changes in central dopamine levels in humans. The observed associations are present in a sample of normal to overweight participants (ie, in the absence of obesity), suggesting that the consumption of a HFS might already be associated with altered behaviours. Alternatively, the effects of HFS diet and obesity might be independent.