What Difference Does it Make? Risk-Taking Behavior in Obesity after a Loss is Associated with Decreased Ventromedial Prefrontal Cortex Activity

Effects of aerobic exercise training in oxidative metabolism and mitochondrial biogenesis markers on prefrontal cortex in obese mice

BACKGROUND

To evaluate the effects of 8 weeks of Aerobic Physical Training (AET) on the mitochondrial biogenesis and oxidative balance in the Prefrontal Cortex (PFC) of leptin deficiency-induced obese mice (ob/ob mice).

METHODS

Then, the mice were submitted to an 8-week protocol of aerobic physical training (AET) at moderate intensity (60% of the maximum running speed). In the oxidative stress, we analyzed Malonaldehyde (MDA) and Carbonyls, the enzymatic activity of Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione S Transferase (GST), non-enzymatic antioxidant system: reduced glutathione (GSH), and Total thiols. Additionally, we evaluated the gene expression of PGC-1α SIRT-1, and ATP5A related to mitochondrial biogenesis and function.

RESULTS

In our study, we did not observe a significant difference in MDA (p = 0.2855), Carbonyl's (p = 0.2246), SOD (p = 0.1595), and CAT (p = 0.6882) activity. However, the activity of GST (p = 0.04), the levels of GSH (p = 0.001), and Thiols (p = 0.02) were increased after 8 weeks of AET. Additionally, there were high levels of PGC-1α (p = 0.01), SIRT-1 (p = 0.009), and ATP5A (p = 0.01) gene expression after AET in comparison with the sedentary group.

CONCLUSIONS

AET for eight weeks can improve antioxidant defense and increase the expression of PGC-1α, SIRT-1, and ATP5A in PFC of ob/ob mice.

The influence of the subcortex and brain stem on overeating: How advances in functional neuroimaging can be applied to expand neurobiological models to beyond the cortex

Functional neuroimaging has become a widely used tool in obesity and eating disorder research to explore the alterations in neurobiology that underlie overeating and binge eating behaviors. Current and traditional neurobiological models underscore the importance of impairments in brain systems supporting reward, cognitive control, attention, and emotion regulation as primary drivers for overeating. Due to the technical limitations of standard field strength functional magnetic resonance imaging (fMRI) scanners, human neuroimaging research to date has focused largely on cortical and basal ganglia effects on appetitive behaviors. The present review draws on animal and human research to highlight how neural signaling encoding energy regulation, reward-learning, and habit formation converge on hypothalamic, brainstem, thalamic, and striatal regions to contribute to overeating in humans. We also consider the role of regions such as the mediodorsal thalamus, ventral striatum, lateral hypothalamus and locus coeruleus in supporting habit formation, inhibitory control of food craving, and attentional biases. Through these discussions, we present proposals on how the neurobiology underlying these processes could be examined using functional neuroimaging and highlight how ultra-high field 7-Tesla (7 T) fMRI may be leveraged to elucidate the potential functional alterations in subcortical networks. Focus is given to how interactions of these regions with peripheral endocannabinoids and neuropeptides, such as orexin, could be explored. Technical and methodological aspects regarding the use of ultra-high field 7 T fMRI to study eating behaviors are also reviewed.

Binge eating disorder

Binge eating disorder (BED) is characterized by regular binge eating episodes during which individuals ingest comparably large amounts of food and experience loss of control over their eating behaviour. The worldwide prevalence of BED for the years 2018-2020 is estimated to be 0.6-1.8% in adult women and 0.3-0.7% in adult men. BED is commonly associated with obesity and with somatic and mental health comorbidities. People with BED experience considerable burden and impairments in quality of life, and, at the same time, BED often goes undetected and untreated. The aetiology of BED is complex, including genetic and environmental factors as well as neuroendocrinological and neurobiological contributions. Neurobiological findings highlight impairments in reward processing, inhibitory control and emotion regulation in people with BED, and these neurobiological domains are targets for emerging treatment approaches. Psychotherapy is the first-line treatment for BED. Recognition and research on BED has increased since its inclusion into DSM-5; however, continuing efforts are needed to understand underlying mechanisms of BED and to improve prevention and treatment outcomes for this disorder. These efforts should also include screening, identification and implementation of evidence-based interventions in routine clinical practice settings such as primary care and mental health outpatient clinics.

Choices of (in)action in obesity: Implications for research on treatment and prevention

The obesity epidemic has crossed social-demographic barriers and is a matter of significant concern. Why do individuals fail to restrain from eating high-calorie foods and fail to follow treatment routines that reduce the risk of health complications? These questions have been addressed through behavioral and brain imaging studies on prefrontal cortex inhibitory mechanisms. Failure to inhibit undesirable behaviors has become a hallmark of obesity. In many life situations, obesity risk is increased by inaction (e.g., not taking blood pressure medication, not following a healthy diet). Risk by inaction has been defined as passive risk-taking, and it is correlated with traits such as procrastination, future time perspective, and cognitive avoidance. To the present, passive tendencies, specifically in the context of risk-taking behaviors, have not been addressed in the obesity literature. We introduce a framework in which active and passive risk-taking behaviors are integrated within the scope of bidirectional models of obesity that describe the brain as both the cause and the consequence of obesity vulnerability. The present perspective aims to foster new research on treatment and prevention, and also on the neurobiology of passive behaviors in obesity and other metabolic conditions.

Executive function in obesity and anorexia nervosa: Opposite ends of a spectrum of disordered feeding behaviour?

Higher-order executive functions such as decision-making, cognitive flexibility and behavioural control are critical to adaptive success in all aspects of life, including the maintenance of a healthy body weight by regulating food intake. Performance on tasks designed to assess these aspects of cognition is impaired in individuals with obesity and anorexia nervosa (AN); conditions at either end of a spectrum of body weight disturbance. While the conceptualisation of obesity and AN as mirror images of each other makes some sense from a metabolic point of view, whether or not these conditions also reflect opposing states of executive function is less clear. Here, we review evidence from neurocognitive and neuroimaging studies to compare the direction and extent of executive dysfunction in subjects with obesity and AN and how these are underpinned by changes in structure and function of subregions of the prefrontal cortex (PFC). Both conditions of extreme body weight disturbance are associated with impaired decision-making and cognitive inflexibility, however, impulsive behaviour presents in opposing directions; obesity being associated with reduced behavioural control and AN being associated with elevated control over behaviour with respect to food and feeding. Accordingly, the subregions of the PFC that guide inhibitory control and valuation of action outcomes (dorsolateral prefrontal cortex and orbitofrontal cortex) show opposite patterns of activation in subjects with obesity compared to those with AN, whereas the subregions implicated in cognitive and behavioural flexibility (ventromedial prefrontal cortex and anterior cingulate cortex) show alterations in the same direction in both conditions but with differential extent of dysfunction. We synthesise these findings in the context of the utility of animal models of obesity and AN to interrogate the detail of the neurobiological contributions to cognition in patient populations and the utility of such detail to inform future treatment strategies that specifically target executive dysfunction.

Clinical factors predicting impaired executive functions in eating disorders: The role of illness duration

Poor performance in executive functions is observed in individuals with eating disorders (EDs). These impairments have usually been associated with the presence of comorbid psychopathology or with higher severity of EDs. However, few studies have explored the interaction between illness duration and deficits in executive functions. The present study investigates the association between ED duration and performance in decision-making, inhibitory control, and cognitive flexibility in the anorexia nervosa restrictive subtype (AN-R), bulimic/purging subtype (AN-BP), and binge spectrum disorders (BSDs) (namely, bulimia nervosa and binge eating disorder) among 116 women with EDs compared with 123 women healthy controls (HCs). Using cumulative survival analysis, we estimated the risk of deficits related to illness duration. Predictors of executive dysfunctions were assessed by regression analysis, including as potential predictors illness duration, severity of general psychopathology, and ED symptomatology. Results showed poor decision-making and cognitive flexibility in participants with EDs compared with HCs. ED duration was associated with poor inhibitory control in the AN-BP group and poor cognitive flexibility in the BSD group. The illness duration increased the risk of presenting early deficits in executive function. In decision-making and inhibitory control, the AN-R group showed the earliest deficits, whereas in cognitive flexibility it was the BSD group. ED duration predicted impaired cognitive flexibility in the BSD group and impaired inhibitory control in the AN-BP group, whereas the severity of general psychopathological symptoms was a predictor of impaired cognitive flexibility in individuals with AN-R. These results highlight the relevance of illness duration in executive dysfunctions in EDs.

Inter-individual body mass variations relate to fractionated functional brain hierarchies

Variations in body mass index (BMI) have been suggested to relate to atypical brain organization, yet connectome-level substrates of BMI and their neurobiological underpinnings remain unclear. Studying 325 healthy young adults, we examined associations between functional connectivity and inter-individual BMI variations. We utilized non-linear connectome manifold learning techniques to represent macroscale functional organization along continuous hierarchical axes that dissociate low level and higher order brain systems. We observed an increased differentiation between unimodal and heteromodal association networks in individuals with higher BMI, indicative of a disrupted modular architecture and hierarchy of the brain. Transcriptomic decoding and gene enrichment analyses identified genes previously implicated in genome-wide associations to BMI and specific cortical, striatal, and cerebellar cell types. These findings illustrate functional connectome substrates of BMI variations in healthy young adults and point to potential molecular associations.

Advances in understanding meso-cortico-limbic-striatal systems mediating risky reward seeking

The risk of an aversive consequence occurring as the result of a reward-seeking action can have a profound effect on subsequent behavior. Such aversive events can be described as punishers, as they decrease the probability that the same action will be produced again in the future and increase the exploration of less risky alternatives. Punishment can involve the omission of an expected rewarding event ("negative" punishment) or the addition of an unpleasant event ("positive" punishment). Although many individuals adaptively navigate situations associated with the risk of negative or positive punishment, those suffering from substance use disorders or behavioral addictions tend to be less able to curtail addictive behaviors despite the aversive consequences associated with them. Here, we discuss the psychological processes underpinning reward seeking despite the risk of negative and positive punishment and consider how behavioral assays in animals have been employed to provide insights into the neural mechanisms underlying addictive disorders. We then review the critical contributions of dopamine signaling to punishment learning and risky reward seeking, and address the roles of interconnected ventral striatal, cortical, and amygdala regions to these processes. We conclude by discussing the ample opportunities for future study to clarify critical gaps in the literature, particularly as related to delineating neural contributions to distinct phases of the risky decision-making process.

The neural correlates of delay discounting in obesity and binge eating disorder

BACKGROUND AND AIMS

Increased delay discounting is associated with obesity and binge eating disorder (BED). Although BED and obesity frequently co-occur, the neural mechanisms underlying delay discounting in these conditions remain poorly understood.

METHODS

Thirtyfive women with obesity, including 10 participants with obesity and BED and 31 controls completed a monetary delay discounting task during functional magnetic resonance imaging.

RESULTS

We identified that increased discounting rates were associated with decreased activity in the left anterior insula in participants with obesity compared to controls when choosing immediate rewards over delayed rewards (PFWE < 0.05). An exploratory analysis comparing the BED subsample to the other groups did not detect significant differences.

DISCUSSION AND CONCLUSIONS

Our findings suggest decreased activity in the anterior insula may underlie heightened delay discounting in individuals with obesity, contributing the probability of choosing immediate rewards over delayed rewards based on emotional states. Future studies including larger, more diverse samples are required to confirm these effects.

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.