Neurobiology of Anorexia and Bulimia Nervosa

The main goal of this study is to explore the effects of hunger and satiety on regions in our brain in order to better understand the pathophysiology underlying restricted eating in anorexics, and overeating in women with Bulimia Nervosa. The investigators will adopt a paradigm that will model, in the laboratory, the naturalistic extremes of dietary intake practiced by women recovered from Anorexia or Bulimia Nervosa by comparing a hungry state (21-hour fast) to a satiated state (21-hour when fed). They may share an inability to precisely modulate emotionality and reward in response to salient stimuli, such as food. However, they may differ in terms of function of other pathways.

The incentive motivational drive to seek and consume food is a complex process, deriving from interrelated psychobiological factors including food's rewarding properties, an individual's homeostatic needs and cognitive ability to favor alternative behaviors. In order to examine how these factors may contribute to dysregulated feeding behavior in women recovered from Anorexia or Bulimia Nervosa, the investigators will explore measures of 1) anxiety; 2) cognitive inhibition and dysinhibition; and 3) reward.

Subjects will also be asked to undergo a Magnetic Resonance Imaging (MRI) scan of their head. This scan uses powerful magnetic fields. The magnetic fields temporarily magnetize some of the chemicals in our brain and this allows a scanner and a computer to take a very detailed picture of the structure of our brain. During the MRI, the participants will be asked to lie quietly inside the center of a large, doughnut shaped magnet for approximately 30 minutes. The participant's head will be placed in a special, helmet-like "head-holder" to help them to keep their head still. This part of the study will take place on the same day prior to the first PET scan. In this protocol, only one MRI will be done. In subjects with a questionable history of metallic fragments, an x-ray of the suspected body area will be performed before the MRI to make sure the participants have no metal fragments in their body.

In addition to fMRI scanning there are a few other tests that will be administered. This includes a Pre Study Taste Test, in order to prepare them for the fMRI taste task. Participants will be presented five solutions of sucrose (2, 4, 8, 16 and 32 weight by volume) and will then be asked to rate the pleasantness of each solution using a standard seven-point preference scale (i.e., 1=extremely dislike; 7= extremely like). They will also rate perceived sweetness of each solution using a seven-point category scale (i.e., 1=absent; 7=extreme). In addition, they will be presented variants of a tasteless solution Study participants will be asked to choose the solution that has the least taste and this solution will then be used during fMRI scanning.

The study takes place over the span of 4 consecutive days on location at the General Clinical Research Center (GCRC) at the University of California in San Diego. During day 1 of the study, lab work would be completed in the morning and several computerized and paper and pencil tasks in the afternoon. Starting at noon of Day 2 and Day 3 of the study, subject participants will undergo two identical 21-hour cycles. In one cycle, study participants will refrain from eating after lunch at 12 noon until 9 a.m. the next morning and they will engage in fMRI studies from 9 to 10:30 a.m. In the other cycle they will be given a standardized diet from noon until 9 a.m. the next day and engage in fMRI studies from 9 to10:30 a.m. The sequence of the two cycles will be randomized across subjects. Caloric consumption will also be regulated. All subjects will receive exactly the same menu over the 4 days of the study. They will eat only when at the GCRC and only when monitored by the GCRC staff. The total daily energy requirement will be calculated as 30 kcal/kg body weight per day with a 53% carbohydrate, 32% fat, 15% protein diet. Water will be provided with the amount consumed recorded. Subjects will be allowed to consume their usual amounts of caffeinated beverages but not allowed to use artificial or natural sweeteners or cream.