Anorexia nervosa and bulimia nervosa have similar phenotypes and clinical courses (
25). Both primarily affect women, and both typically begin in adolescence. Anorexia includes a relentless preoccupation with body shape and weight and repetitive ritualized behaviors that maintain abnormally low body weight (
43). Individuals with anorexia have perfectionist and obsessive temperaments that persist following recovery (
95). Their rigid control over feeding behaviors seems to suggest the presence of pathological self-regulation.
Approximately one-third of adults with bulimia describe past histories of anorexia (
96), and a significant proportion of patients with anorexia regularly binge eat or purge (
25). The high rates of diagnostic crossover between these disorders (
22) suggest that anorexia and bulimia, similar to Tourette’s syndrome and OCD, may be manifestations of the same or comparable underlying disease processes. In addition, their phenotypic similarities, such as an intense preoccupation with food and a high prevalence of OCD and obsessive-compulsive personality traits (
97–
99) that predict poor outcome (
100), suggest that these disorders share neural substrates. Anorexia and bulimia therefore appear to lie on a spectrum of self-regulatory control over feeding behaviors, with excessive control present in anorexia restricting subtype, less control present in anorexia binge/purge subtype, and a paucity of control in bulimia (
101). However, individuals with anorexia have difficulty controlling their obsessive preoccupation with thinness and their ritualistic behaviors that pertain to eating and exercising (
102). Thus, similar to OCD, symptoms of anorexia may represent a failure to shift or to regulate attentional resources away from the intrusive thoughts that motivate calorie restriction and produce ritualistic behaviors. Alternatively, the ritualistic behaviors in anorexia and OCD may represent a failure to regulate the behaviors themselves.
Several lines of evidence point to abnormalities of the anterior cingulate cortex in both ill and recovered persons with anorexia. First, decreased volumes of the dorsal anterior cingulate cortex have been reported in ill (
103) and recovered (
104) adult patients relative to comparison subjects. Second, SPECT studies suggest that adults with anorexia have lower resting regional cerebral blood flow in the anterior cingulate cortex relative to comparison subjects, both before and after weight restoration (
105). Third, PET studies report alterations in postsynaptic serotonin 5-HT
1A and 5-HT
2A receptors in the anterior cingulate cortex in both ill (
106) and recovered (
107) patients. These receptors mediate, respectively, the inhibitory and excitatory actions of 5-HT on cortical neurons (
108); thus these alterations may produce further functional abnormalities in the anterior cingulate cortex. Given the central role of this region in self-regulatory control (
27), these abnormalities seem likely to contribute to self-regulatory disturbances in patients with anorexia (
78).
Although anorexia typically arises during adolescence (
25), imaging data from adolescent patients are sparse, possibly because the confounding effects of malnutrition make findings from studies of patients in the underweight state difficult to interpret. Reduced volumes of total gray matter have been reported in both adolescents and adults with anorexia during acute illness (
109,
110). One study (
109) reported that these deficits persisted in the recovered state, but several additional studies (
110–
112) have reported that gray matter volumes normalize following recovery. Whether or not these anatomical abnormalities simply reflect the transitory effects of malnourishment is unknown.
Most fMRI studies of individuals with anorexia have used symptom provocation designs that expose participants to food-related stimuli (
113,
114). In one study (
114), for example, both ill and recovered women with anorexia activated the medial prefrontal and anterior cingulate cortices more than comparison subjects in response to food compared with nonfood stimuli, suggesting that activation of the frontal cortex to food stimuli represents trait rather than state markers in anorexia. Recovered patients engaged the lateral prefrontal cortex more than ill patients. Similar to findings from persons with OCD (
65), activation of the lateral prefrontal cortex during symptom provocation may reflect the better ability of recovered patients to control their anxiety and preoccupation with food stimuli, consistent with the role that the lateral prefrontal cortex plays in cognitive control (
12).
Findings from fMRI studies suggest that reward processing is dysfunctional in persons with anorexia. In one study that involved a guessing game (
93), women with anorexia activated the ventral striatum similarly during their responses to both positive and negative feedback. Healthy participants, in contrast, activated the ventral striatum preferentially in response to positive feedback, consistent with prior findings of ventral striatal responses to reward but not punishment during this task in healthy participants (
115). PET studies have also reported increased D
2/D
3 receptor binding in the ventral striatum both before and after recovery in patients with anorexia (
94), possibly explaining their abnormal brain activity during reward processing. Dysfunction in the ventral striatum and related portions of frontostriatal circuits that subserve reward processing may contribute to a diminished motivation to eat in individuals with anorexia. Food may not be as rewarding to them as it is to others (
116).
Dysfunction in this circuit, including abnormal activation of the ventral striatum during negative feedback (
93), may also contribute to the diminished motivation of these individuals to avoid negative consequences, such as starvation and repeated hospitalization. Whereas decreases in the numbers of striatal D
2 receptors in obese individuals (
117) may reduce self-regulatory control and promote overeating, increases in the numbers of D
2 receptors in persons with anorexia may enhance self-regulatory control and promote abstention from eating. Excessive control may thereby contribute to the remarkable capacity of individuals with anorexia to deny themselves the gratification of food ingestion in the service of attaining a thinner body.
Unrealistically high personal standards and excessive concerns with making mistakes are common in patients with either anorexia or OCD (
118,
119). Consistent with these phenotypic traits, persons with OCD activated the anterior cingulate cortex more during the commission of errors than healthy comparison subjects on tasks that required inhibitory control, suggesting the presence of a hyperactive error monitoring system (
69,
70,
120). However, acutely ill patients with anorexia activated the anterior cingulate cortex less than comparison subjects during the commission of errors on a flanker task (
121). These differences in activity within error monitoring circuits across anorexia and OCD groups are surprising, given the perfectionism and excessive concern with making mistakes that are common in both disorders.