Those with bulimia nervosa suffer from cyclical binge-and-purge episodes, often severely limiting food only to give in to the tension and eat a large number of calories in one sitting. As discussed on examiner.com, a study released by the University of Colorado Hospital shows that the behavior actually changes the brain over time. What begins as a choice becomes a compulsion. Those who eat a large number of calories in a relatively short amount of time, followed by an episode of purging through self-induced vomiting or laxative use eventually do so because there has been a significant change in the brain that promotes the behavior. Much like a drug addict begins use through the choice of trying the drug, the person with bulimia makes an initial choice, but before long it becomes a compulsion. The area of the brain that issues pleasant rewards begins to not only enjoy that stimulus, but require it, says study author Dr. Guido Frank, psychiatrist at Children's Hospital in Colorado. The study involved 41 participants, and found that the more episodes of binge-and-purge a participant had experienced, the more the brain had changed its reward functions. Dr. Frank reports that the individuals were increasingly anxious before an episode, exhibiting even depressive symptoms. After an episode, the subjects were observed to exhibit a type of "after glow."