Valence Encoding Signals in the Human Amygdala and the Willingness to Eat

Understanding human amygdala function with artificial neural networks

The amygdala is a cluster of subcortical nuclei that receives diverse sensory inputs and projects to the cortex, midbrain and other subcortical structures. Numerous accounts of amygdalar contributions to social and emotional behavior have been offered, yet an overarching description of amygdala function remains elusive. Here we adopt a computationally explicit framework that aims to develop a model of amygdala function based on the types of sensory inputs it receives, rather than individual constructs such as threat, arousal, or valence. Characterizing human fMRI signal acquired as participants viewed a full-length film, we developed encoding models that predict both patterns of amygdala activity and self-reported valence evoked by naturalistic images. We use deep image synthesis to generate artificial stimuli that distinctly engage encoding models of amygdala subregions that systematically differ from one another in terms of their low-level visual properties. These findings characterize how the amygdala compresses high-dimensional sensory inputs into low-dimensional representations relevant for behavior.

A randomized controlled trial investigating the effect of liraglutide on self-reported liking and neural responses to food stimuli in participants with obesity

BACKGROUND/OBJECTIVES

Obesity is a complex condition and the mechanisms involved in weight gain and loss are not fully understood. Liraglutide, a GLP-1 receptor agonist, has been demonstrated to successfully promote weight loss in patients with obesity (OB). Yet, it is unclear whether the observed weight loss is driven by an alteration of food liking. Here we investigated the effects of liraglutide on food liking and the cerebral correlates of liking in OB.

SUBJECTS/METHODS

This study was a randomized, single-center, double-blind, placebo-controlled, parallel group, prospective clinical trial. 73 participants with OB and without diabetes following a multidisciplinary weight loss program, were randomly assigned (1:1) to receive liraglutide 3.0 mg (37.40 ± 11.18 years old, BMI = 35.89 ± 3.01 kg) or a placebo (40.04 ± 14.10 years old, BMI = 34.88 ± 2.87 kg) subcutaneously once daily for 16 weeks.

INTERVENTIONS/METHODS

We investigated liking during food consumption. Participants reported their hedonic experience while consuming a high-calorie food (milkshake) and a tasteless solution. The solutions were administered inside the scanner with a Magnetic Resonance Imaging (MRI)-compatible gustometer to assess neural responses during consumption. The same procedure was repeated during the pre- and post-intervention sessions.

RESULTS

None of the effects involving the intervention factor reached significance when comparing liking between the pre- and post-intervention sessions or groups. Liking during food reward consumption was associated with the activation of the ventromedial prefrontal cortex (vmPFC) and the amygdala. The liraglutide group lost more weight (BMI post-pre = -3.19 ± 1.28 kg/m2) than the placebo group (BMI post-pre = -0.60 ± 1.26 kg/m2).

CONCLUSIONS

These results suggest that liraglutide leads to weight loss without self-report or neural evidence supporting a concomitant reduction of food liking in participants with OB.

Daring to Feel: Emotion-Focused Psychotherapy Increases Amygdala Activation and Connectivity in Euthymic Bipolar Disorder-A Randomized Controlled Trial

BACKGROUND

In bipolar disorder (BD), the alternation of extreme mood states indicates deficits in emotion processing, accompanied by aberrant neural function of the emotion network. The present study investigated the effects of an emotion-centered psychotherapeutic intervention on amygdala responsivity and connectivity during emotional face processing in BD.

METHODS

In a randomized controlled trial within the multicentric BipoLife project, euthymic patients with BD received one of two interventions over 6 months: an unstructured, emotion-focused intervention (FEST), where patients were guided to adequately perceive and label their emotions (n = 28), or a specific, structured, cognitive behavioral intervention (SEKT) (n = 31). Before and after interventions, functional magnetic resonance imaging was conducted while patients completed an emotional face-matching paradigm (final functional magnetic resonance imaging sample of patients completing both measurements: SEKT, n = 17; FEST, n = 17). Healthy control subjects (n = 32) were scanned twice after the same interval without receiving any intervention. Given the focus of FEST on emotion processing, we expected FEST to strengthen amygdala activation and connectivity.

RESULTS

Clinically, both interventions stabilized patients' euthymic states in terms of affective symptoms. At the neural level, FEST versus SEKT increased amygdala activation and amygdala-insula connectivity at postintervention relative to preintervention time point. In FEST, the increase in amygdala activation was associated with fewer depressive symptoms (r = 0.72) 6 months after intervention.

CONCLUSIONS

Enhanced activation and functional connectivity of the amygdala after FEST versus SEKT may represent a neural marker of improved emotion processing, supporting the FEST intervention as an effective tool in relapse prevention in patients with BD.

Habenular connectivity predict weight loss and negative emotional-related eating behavior after laparoscopic sleeve gastrectomy

Habenular (Hb) processes negative emotions that may drive compulsive food-intake. Its functional changes were reported following laparoscopic-sleeve-gastrectomy (LSG). However, structural connectivity (SC) of Hb-homeostatic/hedonic circuits after LSG remains unclear. We selected regions implicated in homeostatic/hedonic regulation that have anatomical connections with Hb as regions-of-interest (ROIs), and used diffusion-tensor-imaging with probabilistic tractography to calculate SC between Hb and these ROIs in 30 obese participants before LSG (PreLSG) and at 12-month post-LSG (PostLSG12) and 30 normal-weight controls. Three-factor-eating-questionnaire (TFEQ) and Dutch-eating-behavior-questionnaire (DEBQ) were used to assess eating behaviors. LSG significantly decreased weight, negative emotion, and improved self-reported eating behavior. LSG increased SC between the Hb and homeostatic/hedonic regions including hypothalamus (Hy), bilateral superior frontal gyri (SFG), left amygdala (AMY), and orbitofrontal cortex (OFC). TFEQ-hunger negatively correlated with SC of Hb-Hy at PostLSG12; and increased SC of Hb-Hy correlated with reduced depression and DEBQ-external eating. TFEQ-disinhibition negatively correlated with SC of Hb-bilateral SFG at PreLSG. Increased SC of Hb-left AMY correlated with reduced DEBQ-emotional eating. Higher percentage of total weight-loss negatively correlated with SC of Hb-left OFC at PreLSG. Enhanced SC of Hb-homeostatic/hedonic regulatory regions post-LSG may contribute to its beneficial effects in improving eating behaviors including negative emotional eating, and long-term weight-loss.

Urbach-Wiethe disease in a young patient without apparent amygdala calcification

Urbach-Wiethe disease is an extremely rare genetically-based syndrome which usually leads to dermatological and neurological changes. Neurologically, the amygdaloid region is primarily bilaterally affected. Therefore, several functions modulated by the amygdala are changed in patients with Urbach-Wiethe disease. As the neurological alterations evolve only gradually, it is particularly important to determine the cognitive and brain status of a juvenile. The patient described here was seen briefly at age 9 and tested neuropsychologically at age 19; furthermore, computer tomography and magnetic resonance imaging of his head was done. There were no important abnormalities in the brain, which is unusual in the light of previous data from other patients. On the cognitive level, the patient was generally within normal limits. However, he had mild problems in attention and concentration, and more prominent problems in emotional processing domain, and in personality dimensions. It is concluded that amygdala calcifications in Urbach-Wiethe disease take place progressively-possibly underpinned by genetic and gender variables; this can subsequently allow psychosocial-social factors (such a proper education and socialization) and biological factors (compensatory neuroplasticity) to retard and diminish the development of socio-emotional and cognitive deteriorations, though the outcome of questionnaires indicates that such patients may develop substantial concerns as to their future life and well-being.

Hypothalamic microstructure and function are related to body mass, but not mental or cognitive abilities across the adult lifespan

Physical, mental, and cognitive resources are essential for healthy aging. Aging impacts on the structural integrity of various brain regions, including the hippocampus. Even though recent rodent studies hint towards a critical role of the hypothalamus, there is limited evidence on functional consequences of age-related changes of this region in humans. Given its central role in metabolic regulation and affective processing and its connections to the hippocampus, it is plausible that hypothalamic integrity and connectivity are associated with functional age-related decline. We used data of n = 369 participants (18-88 years) from the Cambridge Centre for Ageing and Neuroscience repository to determine functional impacts of potential changes in hypothalamic microstructure across the lifespan. First, we identified age-related changes in microstructure as a function of physical, mental, and cognitive health and compared those findings to changes in hippocampal microstructure. Second, we investigated the relationship of hypothalamic microstructure and resting-state functional connectivity and related those changes to age as well as physical health. Our results showed that hypothalamic microstructure is not affected by depressive symptoms (mental health), cognitive performance (cognitive health), and comparatively stable across the lifespan, but affected by body mass (physical health). Furthermore, body mass changes connectivity to limbic regions including the hippocampus, amygdala, and nucleus accumbens, suggesting functional alterations in the metabolic and reward systems. Our results demonstrate that hypothalamic structure and function are affected by body mass, focused on neural density and dispersion, but not inflammation. Still, observed effect sizes were small, encouraging detailed investigations of individual hypothalamic subunits.

Task-Dependent Effective Connectivity of the Reward Network During Food Cue-Reactivity: A Dynamic Causal Modeling Investigation

Neural reactivity to food cues may play a central role in overeating and excess weight gain. Functional magnetic resonance imaging (fMRI) studies have implicated regions of the reward network in dysfunctional food cue-reactivity, but neural interactions underlying observed patterns of signal change remain poorly understood. Fifty overweight and obese participants with self-reported cue-induced food craving viewed food and neutral cues during fMRI scanning. Regions of the reward network with significantly greater food versus neutral cue-reactivity were used to specify plausible models of task-related neural interactions underlying the observed blood oxygenation level-dependent (BOLD) signal, and a bi-hemispheric winning model was identified in a dynamic causal modeling (DCM) framework. Neuro-behavioral correlations are investigated with group factor analysis (GFA) and Pearson's correlation tests. The ventral tegmental area (VTA), amygdalae, and orbitofrontal cortices (OFC) showed significant food cue-reactivity. DCM suggests these activations are produced by largely reciprocal dynamic signaling between these regions, with food cues causing regional disinhibition and an apparent shifting of activity to the right amygdala. Intrinsic self-inhibition in the VTA and right amygdala is negatively correlated with measures of food craving and hunger and right-amygdalar disinhibition by food cues is associated with the intensity of cue-induced food craving, but no robust cross-unit latent factors were identified between the neural group and behavioral or demographic variable groups. Our results suggest a rich array of dynamic signals drive reward network cue-reactivity, with the amygdalae mediating much of the dynamic signaling between the VTA and OFCs. Neuro-behavioral correlations suggest particularly crucial roles for the VTA, right amygdala, and the right OFC-amygdala connection but the more robust GFA identified no cross-unit factors, so these correlations should be interpreted with caution. This investigation provides novel insights into dynamic circuit mechanisms with etiologic relevance to obesity, suggesting pathways in biomarker development and intervention.

Amygdala function in emotion, cognition, and behavior

The amygdala is a core structure in the anterior medial temporal lobe, with an important role in several brain functions involving memory, emotion, perception, social cognition, and even awareness. As a key brain structure for saliency detection, it triggers and controls widespread modulatory signals onto multiple areas of the brain, with a great impact on numerous aspects of adaptive behavior. Here we discuss the neural mechanisms underlying these functions, as established by animal and human research, including insights provided in both healthy and pathological conditions.

Extrahypothalamic Control of Energy Balance and Its Connection with Reproduction: Roles of the Amygdala

Body energy and metabolic homeostasis are exquisitely controlled by multiple, often overlapping regulatory mechanisms, which permit the tight adjustment between fuel reserves, internal needs, and environmental (e.g., nutritional) conditions. As such, this function is sensitive to and closely connected with other relevant bodily systems, including reproduction and gonadal function. The aim of this mini-review article is to summarize the most salient experimental data supporting a role of the amygdala as a key brain region for emotional learning and behavior, including reward processing, in the physiological control of feeding and energy balance. In particular, a major focus will be placed on the putative interplay between reproductive signals and amygdala pathways, as it pertains to the control of metabolism, as complementary, extrahypothalamic circuit for the integral control of energy balance and gonadal function.

Valence encoding in the amygdala influences motivated behavior

The amygdala is critical for emotional processing and motivated behavior. Its role in these functions is due to its processing of the valence of environmental stimuli. The amygdala receives direct sensory input from sensory thalamus and cortical regions to integrate sensory information from the environment with aversive and/or appetitive outcomes. As many reviews have discussed the amygdala's role in threat processing and fear conditioning, this review will focus on how the amygdala encodes positive valence and the mechanisms that allow it to distinguish between stimuli of positive and negative valence. These findings are also extended to consider how valence encoding populations in the amygdala contribute to local and long-range circuits including those that integrate environmental cues and positive valence. Understanding the complexity of valence encoding in the amygdala is crucial as these mechanisms are implicated in a variety of disease states including anxiety disorders and substance use disorders.