Are you the kind of person who enjoys a new episode of Downton Abbey every Sunday? Maybe you prefer to get each episode as soon as possible — it is just too hard to wait until the end of the season. Perhaps waiting for each new episode brings its own reward.
Or do you wait until the end of the season, and settle in for a good long watch of the entire season in one sitting – so-called “binge watching.” In this case, the anticipation could be part of the fun. Perhaps waiting until the season is over brings its own reward.
These television viewing styles amount to a choice between a small, relatively instant, reward (one episode weekly) or a larger reward after a delay (multiple episodes in one sitting at the season’s end). Different people will have a different tolerance for how long they are willing to wait, and what is worth the wait.
We examined this phenomenon – referred to in scientific circles as “delayed discounting” – among individuals with anorexia nervosa in our study “On Weight and Waiting,” recently published in Biological Psychiatry. The decision to limit intake in anorexia nervosa is critical to fully understand, as this behavior promotes starvation and thereby keeps this dangerous illness going. The decision to forgo food in the moment can be thought of as a preference for the future reward of possible weight loss. In our study, we used choices between different amounts of money as a way to ask patients with anorexia nervosa how they might think about different rewards over time.
The decision between monetary rewards available now versus later has been greatly studied in a corner of science called behavioral economics. The brain systems that underlie this choice have even been identified: the limbic system is active when choosing the immediate reward while the lateral prefrontal cortex seems important when deciding to wait. One real-life example of this phenomenon is the way interest rates are set: in order to make it worth it for people to save money, interest rates are set just high enough that it is generally worth the wait. Perhaps, in anorexia nervosa, the brain is computing that the value of eating something now is less than the value of delaying eating, which in turn can come with weight loss – perhaps the future weight loss is the interest on the reward that makes it worth waiting for.
To examine this characteristic in anorexia nervosa, we asked a group of adult patients who were receiving treatment to help us learn about their decision-making preferences. We asked a series of questions about preferences for different amounts of money. For example, would you prefer that we give you $5 right after this procedure today, or that we give you $10 4 weeks from now? What if none of the money was available today – would you prefer that we give you $5 in 2 weeks, or a larger amount, say $20, in 6 weeks?
Essentially the question we were asking was this: How much more money does it need to be to make it worth waiting for?
Based on an earlier study, we expected people with anorexia nervosa to be more willing to wait for the money. We guessed that this might be a personality feature – one that maybe even facilitates the ability to forgo food – and therefore we would still see a preference for later reward after treatment. There is nothing about anorexia nervosa that relates to decisions about money. Nonetheless, if it is a personality feature then this behavior would theoretically exist even in decisions less emotionally fraught than those related to eating.
Much of what we found surprised us. As predicted, people with anorexia nervosa did indeed show a preference for the later reward, when compared to similar individuals with no eating disorder. However, after achieving a healthy weight (and all the treatment that goes with that), these same individuals made their choices no differently than people who had never had an eating disorder.
Even more unexpected, the brain activity was not what we had guessed. The brain areas that are commonly thought to underlie self-control (prefrontal cortex regions) looked like the healthy controls.
The difference we did find was in a part of the brain generally associated with evaluating the reward itself (the striatum). When underweight and therefore prone to choosing the delayed reward, individuals with anorexia nervosa showed less neural activity (compared with healthy controls) in the striatum, a part of the brain that is known for processing rewards.
Even more surprising, after treatment – when the choice differences between patients and controls had disappeared – there were differences in neural activity in a broader network of regions that help to process rewards. After treatment, the patients showed increases in activity in the striatum and in parts of the cortex. It was as though these areas of reward processing had to work harder than healthy peers in order to choose the immediate reward.
These findings raise more questions than they answer. We correctly predicted that people with anorexia nervosa show more interest in waiting for rewards, but we did not find that this was a simple matter of hyperactive control activity in the brain. The common clinical characterization that these individuals possess “extreme willpower” is contradicted by these findings.
This study certainly further confirms that anorexia nervosa comes with very complicated experiences of reward. Successful weight restoration treatment may help to change these processes and perhaps encourage patients to appreciate the value of small rewards. To better understand what drives people to make recurrent choices to eschew adequate nourishment – and what helps them change these habits – we need to understand how individuals with anorexia nervosa process these decisions.
We are, as always, indebted to the many patients with anorexia nervosa who contributed to this research by their participation.
For more information on current eating disorders research at our program, please read about our latest studies, call us at 646-774-8066, or email us at edru@nyspi.columbia.edu.
