فعال سازی مغز در طول ادراک تصاویر بدن تحریف شده در اختلالات تغذیه ای

Eating disorder (ED) patients have severe disturbances in the perception of body shape and weight. The authors investigated brain activation patterns during the perception of distorted body images in various subtypes of ED. Participants comprised 33 patients with EDs (11 with restricting-type anorexia nervosa (AN-R), 11 with binging–purging type anorexia nervosa (AN-BP), 11 with bulimia nervosa (BN)) and 11 healthy women. Functional magnetic resonance imaging was used to examine cerebral response to morphed images of subjects' own bodies, as well as that of another woman. The amygdala was significantly activated in AN-R patients, AN-BP patients, and healthy women in response to their own fat-image, but this did not occur in BN patients. The prefrontal cortex (PFC) was significantly activated in AN-BP patients and healthy women, but not in AN-R and BN patients. Our results showed that the various EDs are different with respect to significant activation of the amygdala and PFC during the processing of participants' own fat-image. Brain activation pattern differences between the various EDs may underlie cognitive differences with respect to distorted body image, and therefore might reflect a general failure to represent and evaluate one's own body in a realistic fashion.

Most women are concerned about their shape and weight (Thompson et al., 1999). Body dissatisfaction is widespread among women in Western societies (Rodin et al., 1993 and Tiggemann and Wilson-Barrett, 1998), possibly as a consequence of sociocultural standards of female beauty that emphasize extreme and, for most women, unattainable thinness (Thompson et al., 1999). Such expectations are thought to be a risk factor for the development of eating disorders (EDs). EDs are an important cause of physical and psychosocial morbidity in young women (Fairburn and Harrison, 2003). EDs are classified primarily into three subtypes, according to specific observable attributes or symptoms (e.g., eating behaviors per se). Anorexia nervosa (AN) and bulimia nervosa (BN) are the two major categories of ED. AN is characterized by the maintenance of an inappropriately low body weight, a relentless pursuit of thinness, and obsessive fears of becoming fat (American Psychiatric Association, 1994). AN is further classified into two subtypes according to specific eating behaviors (American Psychiatric Association, 1994): The restricting type (AN-R; severe restriction of food intake with no associated binging or purging behaviors) and the binge eating/purging type (AN-BP; restriction of food intake coupled with episodes of binge eating/purging). BN is characterized by frequent episodes of uncontrolled overeating (binging). Most EDs are characterized by abnormalities in perception and evaluation of body shape (Uher et al., 2005). Cognitive biases or distortions, particularly about body weight and shape, have been well documented among ED patients. These distortions include biases in the interpretation of body-related information. Related to concerns about weight and shape in EDs is “a disturbance in the way in which one's body weight or shape is experienced” (American Psychiatric Association, 1994). This manifests as systematic overestimation of one's own size, and this bias is stronger in AN than in BN (Cash and Deagle, 1997). Consistent with these cognitive biases, ED patients might have functional abnormalities in those brain systems that are concerned with the processing of body size or image (Grunwald et al., 2001 and Smeets and Kosslyn, 2001). Recently, brain imaging techniques such as functional magnetic resonance imaging (fMRI) have been used to identify specific areas that might underlie abnormal brain functioning in ED patients. The propensity to display specific attributes (drive for thinness, fear of fatness) and behaviors (restricting, binge eating) can be conceptualized as preferential activation of certain neural pathways and circuits (Uher et al., 2005). Several fMRI studies of EDs have investigated brain activation during the presentation of body shape images. Two previous fMRI studies have investigated the neuroanatomical effects of exposing AN patients to morphed images of their own bodies (Seeger et al., 2002 and Wagner et al., 2003). Whereas a pilot study of three patients reported specific responses in the right amygdala, right fusiform gyrus and brainstem to AN patients' own bodies relative to another woman's (Seeger et al., 2002), a group analysis of 13 patients did not replicate these findings (Wagner et al., 2003). The latter authors explain this discrepancy as a consequence of task design. Brain imaging data on BN are even more limited. One fMRI study found that the lateral fusiform gyrus, inferior parietal cortex, and lateral prefrontal cortex (PFC) were activated in response to line drawings of body shapes (compared with a control condition) in AN patients, BN patients, and healthy women (Uher et al., 2005). One positron emission tomography (PET) study reported that brain serotonin alterations were present after recovery from BN (Kaye et al., 2001). Our previous study reported that healthy women showed activation of the limbic/paralimbic areas and PFC upon viewing distorted images of their own bodies (Kurosaki et al., 2006). These investigations suggest that there is a specific neural network that is involved in the general processing of body shapes (the lateral fusiform, parietal and dorsolateral PFC (DLPFC)) (Uher et al., 2005 and Downing et al., 2001), with the emotional (e.g., the amygdala per se) and self-referential areas (medial PFC (MPFC)) (Fossati et al., 2003, Johnson et al., 2002 and Zysset et al., 2002) activated when body-shape-related stimuli carry significant emotional or self-related information (Friederich et al., 2007). Further evidence for the notion of a specific neural network for body shape processing comes from lesion studies, in which lesions of the DLPFC and/or parietal cortex are associated with impaired performance on tasks that require on-line coding of body posture (Schwoebel and Coslett, 2005). However, there have been no studies of brain activation differences upon viewing distorted images of one's own body among the three major subtypes of ED (AN-R, AN-BP, and BN). Similarly, little is known about possible functional abnormalities in brain systems that might underlie the cognitive/emotional differences amongst the three subtypes of ED. In the present study, we investigated the neural correlates of body-image perception in three subtypes of EDs and healthy women, examining cerebral responses to morphed images of subjects' own bodies as well as that of another woman. We hypothesized that brain activation differences during the processing of body-image stimuli across the groups would involve discrepancies in activation of the limbic area including the amygdala, and the PFC. We used fMRI to capture brain activation while participants engaged in a “body-image task” that required them to perceive distorted images and real images of their own (and others') bodies.