Volume and Connectivity Differences in Brain Networks Associated with Cognitive Constructs of Binge Eating.

Bulimia nervosa (BN) and binge eating disorder (BED) are characterized by episodes of eating large amounts of food while experiencing a loss of control. Recent studies suggest that the underlying causes of BN/BED consist of a complex system of environmental cues, atypical processing of food stimuli, altered behavioral responding, and structural/functional brain differences compared with healthy controls (HC). In this narrative review, we provide an integrative account of the brain networks associated with the three cognitive constructs most integral to BN and BED, namely increased reward sensitivity, decreased cognitive control, and altered negative affect and stress responding. We show altered activity in BED/BN within several brain networks, specifically in the striatum, insula, prefrontal cortex (PFC) and orbitofrontal cortex (OFC), and cingulate gyrus. Numerous key nodes in these networks also differ in volume and connectivity compared with HC. We provide suggestions for how this integration may guide future research into these brain networks and cognitive constructs.

Dopaminergic and noradrenergic modulation of stress-induced alterations in brain activation associated with goal-directed behaviour.

BACKGROUND: Acute stress is thought to reduce goal-directed behaviour, an effect purportedly associated with stress-induced release of catecholamines. In contrast, experimentally increased systemic catecholamine levels have been shown to increase goal-directed behaviour. Whether experimentally increased catecholamine function can modulate stress-induced reductions in goal-directed behaviour and its neural substrates, is currently unknown. AIM: To assess whether and how experimentally induced increases in dopamine and noradrenaline contribute to the acute stress effects on goal-directed behaviour and associated brain activation. METHODS: One hundred participants underwent a stress induction protocol (Maastricht acute stress test; MAST) or a control procedure and received methylphenidate (MPH) (40 mg, oral) or placebo according to a 2 × 2 between-subjects design. In a well-established instrumental learning paradigm, participants learnt stimulus-response-outcome associations, after which rewards were selectively devalued. Participants' brain activation and associated goal-directed behaviour were assessed in a magnetic resonance imaging scanner at peak cortisol/MPH concentrations. RESULTS: The MAST and MPH increased physiological measures of stress (salivary cortisol and blood pressure), but only MAST increased subjective measures of stress. MPH modulated stress effects on activation of brain areas associated with goal-directed behaviour, including insula, putamen, amygdala, medial prefrontal cortex, frontal pole and orbitofrontal cortex. However, MPH did not modulate the tendency of stress to induce a reduction in goal-directed behaviour. CONCLUSION: Our neuroimaging data suggest that MPH-induced increases in dopamine and noradrenaline reverse stress-induced changes in key brain regions associated with goal-directed behaviour, while behavioural effects were absent. These effects may be relevant for preventing stress-induced maladaptive behaviour like in addiction or binge eating disorder.

Balancing Between Goal-Directed and Habitual Responding Following Acute Stress.

Instrumental learning is regulated by two memory systems: a relatively rigid but efficient habit system and a flexible but resource-demanding goal-directed system. Previous work has demonstrated that exposure to acute stress may shift the balance between these systems toward the habitual system. In the current study, we used a 2-day outcome devaluation paradigm with a 75% reward contingency rate and altered food reward categories to replicate and extend our previous findings. Participants learned neutral stimulus-response-reward associations on the first day. On the second day, rewards were devalued by eating to satiety. Subsequently, acute stress was induced in half of the participants using the Maastricht Acute Stress Test, while the other half engaged in a nonstressful control task. Finally, relative goal-directed versus habitual behavior was evaluated in a slips-of-action phase, where more slips-of-action indicate a shift toward the habitual system. Results showed that participants successfully acquired the stimulus-response-reward associations, that devaluation was effective, and that stressed participants displayed significant increases in cortisol and blood pressure. Stress led participants to commit more slips-of-action compared with nonstressed controls. The current study extends previous work, showing that the employed paradigm and outcome devaluation procedure are boundary conditions to the stress-induced shift in instrumental responding.

Human Lateral Frontal Pole Contributes to Control over Emotional Approach-Avoidance Actions.

Regulation of emotional behavior is essential for human social interactions. Recent work has exposed its cognitive complexity, as well as its unexpected reliance on portions of the anterior PFC (aPFC) also involved in exploration, relational reasoning, and counterfactual choice, rather than on dorsolateral and medial prefrontal areas involved in several forms of cognitive control. This study anatomically qualifies the contribution of aPFC territories to the regulation of prepotent approach-avoidance action tendencies elicited by emotional faces, and explores a possible structural pathway through which this emotional action regulation might be implemented. We provide converging evidence from task-based fMRI, diffusion-weighted imaging, and functional connectivity fingerprints for a novel neural element in emotional regulation. Task-based fMRI in human male participants (N = 40) performing an emotional approach-avoidance task identified aPFC territories involved in the regulation of action tendencies elicited by emotional faces. Connectivity fingerprints, based on diffusion-weighted imaging and resting-state connectivity, localized those task-defined frontal regions to the lateral frontal pole (FPl), an anatomically defined portion of the aPFC that lacks a homologous counterpart in macaque brains. Probabilistic tractography indicated that 10%-20% of interindividual variation in emotional regulation abilities is accounted for by the strength of structural connectivity between FPl and amygdala. Evidence from an independent replication sample (N = 50; 10 females) further substantiated this result. These findings provide novel neuroanatomical evidence for incorporating FPl in models of control over human action tendencies elicited by emotional faces.SIGNIFICANCE STATEMENT Successful regulation of emotional behaviors is a prerequisite for successful participation in human society, as is evidenced by the social isolation and loss of occupational opportunities often encountered by people suffering from emotion regulation disorders, such as social-anxiety disorder and psychopathy. Knowledge about the precise cortical regions and connections supporting this control is crucial for understanding both the nature of computations needed to successfully traverse the space of possible actions in social situations, and the potential interventions that might result in efficient treatment of social-emotional disorders. This study provides evidence for a precise cortical region (lateral frontal pole) and a structural pathway (the ventral amygdalofugal bundle) through which a cognitively complex form of emotional action regulation might be implemented in the human brain.

Lateral frontal pole and relational processing: Activation patterns and connectivity profile.

The functional contribution of the lateral frontal cortex to behavior has been discussed with reference to several higher-order cognitive domains. In a separate line of research, recent studies have focused on the anatomical organization of this part of the brain. These different approaches are rarely combined. Here, we combine previous work using anatomical connectivity that identified a lateral subdivision of the human frontal pole and work that suggested a general role for rostrolateral prefrontal cortex in processing higher-order relations, irrespective of the type of information. We asked healthy human volunteers to judge the relationship between pairs of stimuli, a task previously suggested to engage the lateral frontal pole. Presenting both shape and face stimuli, we indeed observed overlapping activation of the lateral prefrontal cortex when subjects judged relations between pairs. Using resting state functional MRI, we confirmed that the activated region's whole-brain connectivity most strongly resembles that of the lateral frontal pole. Using diffusion MRI, we showed that the pattern of connections of this region with the main association fibers again is most similar to that of the lateral frontal pole, consistent with the observation that it is this anatomical region that is involved in relational processing.