Brain hypometabolism of glucose in low-weight depressed patients and in anorectic patients: a consequence of starvation?

Neuroimaging of psychiatric disorders

Psychiatry remains the only medical specialty where diagnoses are still based on clinical syndromes rather than measurable biological abnormalities. As imaging technology and analytical methods evolve, it is becoming clear that subtle but measurable radiological characteristics exist and can be used to experimentally classify psychiatric disorders, predict response to treatment and, hopefully, develop new, more effective therapies. This review highlights advances in neuroimaging modalities that are now allowing assessment of brain structure, connectivity and neural network function, describes technical aspects of the most promising methods, and summarizes observations made in some frequent psychiatric disorders.

The neurobiology of eating disorders--a clinical perspective

OBJECTIVE

To provide a neurobiological basis of eating disorders for clinicians and to enlighten how comparing neurobiology and eating disorders with neurobiology of other psychiatric illnesses can improve treatment protocols.

METHOD

A selective review on the neurobiology of eating disorders. The article focuses on clinical research on humans with consideration of the anatomical, neural, and molecular basis of eating disorders.

RESULTS

The neurobiology of people with eating disorders is altered. Many of the neurobiological regions, receptors, and chemical substrates that are affected in other mental illnesses also play an important role in eating disorders. More knowledge about the neurobiological overlap between eating disorders and other psychiatric populations will help when developing treatment protocols not the least regarding that comorbidity is common in patients with EDs.

CONCLUSION

Knowledge about the underlying neurobiology of eating disorders will improve treatment intervention and will benefit from comparisons with other mental illnesses and their treatments.

Neurocircuitry of limbic dysfunction in anorexia nervosa

Anorexia Nervosa (AN) is a serious psychiatric condition marked by firmly entrenched and maladaptive behaviors and beliefs about body, weight and food, as well as high rates of psychiatric comorbidity. The neural roots of AN are now beginning to emerge, and appear to be related to dysfunctional, primarily limbic, circuits driving pathological thoughts and behaviors. As a result, the significant physical symptoms of AN are increasingly being understood at least partially as a result of abnormal or dysregulated emotional processing. This paper reviews the nature of limbic dysfunction in AN, and how structural and functional imaging has implicated distinct emotional and perceptual neural circuits driving AN symptoms. We propose that top-down and bottom-up influences converge on key limbic modulatory structures, such as the subcallosal cingulate and insula, whose normal functioning is critical to affective regulation and emotional homeostasis. Dysfunctional activity in these structures, as is seen in AN, may lead to emotional processing deficits and psychiatric symptoms, which then drive maladaptive behaviors. Modulating limbic dysregulation may therefore be a potential treatment strategy in some AN patients.

The neurobiology of anorexia nervosa: a systematic review

OBJECTIVE

Recent advances in neuroimaging techniques have enabled a better understanding of the neurobiological underpinnings of anorexia nervosa (AN). The aim of this paper was to summarise our current understanding of the neurobiology of AN.

METHODS

The literature was searched using the electronic databases PubMed and Google Scholar, and by additional hand searches through reference lists and specialist eating disorders journals. Relevant studies were included if they were written in English, only used human participants, had a specific AN group, used clinical populations of AN, group comparisons were reported for AN compared to healthy controls and not merely AN compared to other eating disorders or other psychiatric groups, and were not case studies.

RESULTS

The systematic review summarises a number of structural and functional brain differences which are reported in individuals with AN, including differences in neurotransmitter function, regional cerebral blood flow, glucose metabolism, volumetrics and the blood oxygen level dependent response.

CONCLUSION

Several structural and functional differences have been reported in AN, some of which reverse and others which persist following weight restoration. These findings have important implications for our understanding of the neurobiological underpinnings of AN, and further research in this field may provide new direction for the development of more effective treatments.

Review

Neuroanatomical and functional studies in the eating disorders (ED) are reviewed. Typically, anorexia nervosa (AN) is associated with cerebral spinal fluid spaces enlargement which generally recover as a function of re-feeding. However, specific cortical areas fail to correct in weight restored anorectic patients suggesting trait-related abnormalities. Functional changes in AN associated with starvation reverse with weight recovery, however, reduced 5-HT2A receptor binding may be fundamental to the pathophysiology of AN since this remains after long term weight restoration. Structural studies of bulimia nervosa (BN) provide evidence of brain atrophy, in the absence of significant weight loss but potentially related to chronic dietary restriction. Functional investigations reveal reduced thalamic and hypothalamic serotonin transporter availability in BN which increases with longer illness duration. Thus, BN is associated with substantial structural and functional alterations despite normal weight. Recent advances in neuroimaging techniques and their interpretation are increasing our understanding of normal processes in the control of food intake including neuroanatomical correlates of hunger and satiety. Taken together with the structural and functional changes observed in the ED, neuroimaging provides a powerful platform to identify the underlying trait-related pathophysiological mechanisms in the aetiology and maintenance of AN and BN.

Towards a neurocircuitry in anorexia nervosa: evidence from functional neuroimaging studies

Functional neuroimaging is widely used to unravel changes in brain functioning in psychiatric disorders. In the current study, we review single-photon emission tomography (SPECT), positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies in anorexia nervosa (AN), a difficult-to-treat eating disorder with the highest mortality rate among psychiatric disorders. We discuss the role of the parietal cortex, anterior and subgenual cingulate cortex, frontal cortex and temporal lobe in light of the cardinal symptoms of AN. The insights of the current review may ultimately lead to the development of new treatments.

Neuroimaging in eating disorders and obesity: implications for research

Medicine and psychiatry have benefited from developments in investigational techniques. Neuroimaging is one such domain that has technically progressed enormously in recent years, resulting in, for example, higher temporal and spatial resolution. Neuroimaging techniques have been widely used in a range of psychiatric disorders, providing new insights into neural brain circuits and neuroreceptor functions in vivo. These imaging techniques allow researchers to study not only the configuration of brain structures but also aspects of normal and anomalous human behavior more accurately.

Laparophobia: a cognitive perspective on appetite control in anorexia nervosa

Decades of research have demonstrated that anorexia nervosa (AN) may be associated with aberrant cognition, yet, its role in maintaining stringent dieting has received relatively little attention from mainstream researchers of eating disorders. The purpose of the present article is to highlight cognitive ('top-down') factors that are considered responsible for anticipatory anxiety of stoutness and frank fat-phobia (laparophobia). A cognitive model proposed departs from the formulation suggesting that phobia of over-eating is superimposed on avoidant tendencies ('environmental autonomy syndrome'), whereas excessive exercising becomes a natural coping strategy with laparophobia, an instrument of reward. AN ideation involves complex neuronal circuitries and multiple neurochemical components that may conceivably represent a mirror image of those underlying obesity. The emphasis on phobia and aberrant membrane excitability akin to channelopathies behoves the clinicians to be aware of potential uses of drugs acting at the gamma-aminobutyric acid and the N-methyl-D-aspartate/AMPA [2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionic acid] receptors sites as the adjuncts to conventional agents in managing AN.

Psychobiology of altered states of consciousness

The article reviews the current knowledge regarding altered states of consciousness (ASC) (a) occurring spontaneously, (b) evoked by physical and physiological stimulation, (c) induced by psychological means, and (d) caused by diseases. The emphasis is laid on psychological and neurobiological approaches. The phenomenological analysis of the multiple ASC resulted in 4 dimensions by which they can be characterized: activation, awareness span, self-awareness, and sensory dynamics. The neurophysiological approach revealed that the different states of consciousness are mainly brought about by a compromised brain structure, transient changes in brain dynamics (disconnectivity), and neurochemical and metabolic processes. Besides these severe alterations, environmental stimuli, mental practices, and techniques of self-control can also temporarily alter brain functioning and conscious experience.

Changes in brain metabolism associated with remission in unipolar major depression

OBJECTIVE

Functional brain correlates of remission in patients with major depressive disorder (MDD) are measured with positron emission tomography (PET) and 18F-fluorodeoxyglucose.

METHOD

Glucose metabolism was measured in patients (n = 41) with moderate to severe MDD during acute depression and in the remitted state defined as a period of asymptomatic condition over 12 weeks. Data analyses used a region-of-interest (ROI) approach and statistical parametric mapping (SPM).

RESULTS

There were significant decreases in metabolism upon remission with respect to the baseline scan in left prefrontal, anterior temporal and anterior cingulate cortex and bilateral thalamus (SPM analysis) and bilateral putamen and cerebellum (SPM and ROI analyses). There was a significant asymmetry in prefrontal and anterior cingulate cortex metabolism with lower metabolism in the left hemisphere that persisted despite clinical remission.

CONCLUSION

These findings support the hypothesis that selective monoamine reuptake inhibition leads to an attenuation of a brain circuit that mediates depressive symptomatology.

Neuroimaging studies in eating disorders

The understanding of the eating disorders (EDs) anorexia (AN) and bulimia nervosa (BN) has undergone remarkable advancements in the past decade. Most studies that have been done in AN show brain gray and white matter volume loss during the ill state that, at least in part, remit with recovery. Similar patterns occur for brain phospholipids assessed using magnet resonance spectroscopy (MRS). Imaging studies have been used to provide functional information regarding serotonin neuroreceptor dynamics, regional cerebral blood flow, or cerebral glucose metabolism. Such studies have implicated cingulate, frontal, temporal, and parietal regions in AN. Investigators have found that challenges such as food and body image distortions may activate some of these regions, raising the possibility that such studies may shed light on puzzling AN symptoms, such as body image distortions or extremes of appetitive behaviors. Emerging data suggest these disturbances persist after recovery from AN, suggesting the possibility that these are traits that may create a vulnerability to develop an ED. While fewer studies have been done in BN or binge eating disorder, there may be disturbances of serotonin metabolism in similar brain regions. Taken together, these findings give promise for future investigations with the hope of delineating brain pathways that contribute to the etiology of EDs