EATING DISORDERS

Dying to Be Perfect: Anorexia Nervosa

What causes people to become anorexic?

Individuals suffering from anorexia nervosa maintain a starvation diet, despite being significantly underweight. This disorder is characterized by restricted behaviour and preoccupation with controlling one’s food intake.

People with anorexia often begin this pattern as a part of a normal diet, which gradually escalates into significant weight loss and extreme dieting behaviour. This escalation can be explained by action-outcome learning, more commonly known as operant conditioning.

The weight loss that comes with dieting is highly rewarding and therefore acts as positive reinforcement. Moreover, the rewards are intermittent as weight loss is not possible on a daily basis and the recognition of the weight change in the patient takes time to occur.

This creates a schedule in which reinforcements are distributed at varying intervals of time, depending on whether or not the desired behaviour has been performed, also known as variable interval reinforcement.

This type of reinforcement produces the highest level of response and the slowest level of extinction of the behaviour. As a result, the dieting behaviour of some people eventually becomes highly resistant to change and develops into a full-blown eating disorder.¹

When an unconditioned stimulus that provokes a fear response is associated with a neutral stimulus, this turns it into a fear-inducing stimulus, also known as the conditioned stimulus.

In the case of individuals with anorexia nervosa, the positive reinforcement is ‘losing weight’ so the unconditioned stimulus is the fear of gaining weight and loss of control. This fear is associated with food because eating food leads to gaining and therefore becomes the conditioned (fear-inducing) stimulus.

Fear extinction can occur through exposure to the conditioned stimulus, which causes a decline in the conditioned fear responses. The avoidance of food and starvation of the self can be seen as the anorexic patient’s conditioned fear response.

The treatment of anorexia nervosa involves exposure-driven therapy, focusing on fear activation, minimization of anxiety-reducing behaviours (e.g. cutting food into smaller pieces), and habituation. Regardless, relapse is common among patients with the disorder. This is because fear memories can last a long time.

Extinction describes a process that uses exposure to a stimulus in order to inhibit fear responses. It was initially seen as the unlearning of fear, however, the fact that relapse is common challenges this assumption. Extinction is also not the same as forgetting. It simply creates a new and safe association between the conditioned and unconditioned stimulus inhibiting the original conditioned fear response. In other words, if there is insufficient inhibition, the fear can come back.

According to studies 35% to 41% of AN patients relapse within 18 months of the treatment.² These patients are particularly challenging because not only weight loss is conditioned as a reward, weight gain and anything that can lead to loss of control are conditioned as fear.

Whenever these patients eat, these two processes compete with each other and if inhibition is not sufficient fear can return.³ This is consistent with other extinction-based therapies such as in the case of phobias, which also see high rates of relapse.⁴

References:

[1]: Walsh, B. T. (2013). The enigmatic persistence of anorexia nervosa. The American journal of psychiatry, 170(5), 477–484. https://doi.org/10.1176/appi.ajp.2012.12081074

[2]: Berends, T., van Meijel, B., Nugteren, W., Deen, M., Danner, U. N., Hoek, H. W., & van Elburg, A. A. (2016). Rate, timing and predictors of relapse in patients with anorexia nervosa following a relapse prevention program: a cohort study. BMC psychiatry, 16(1), 316. https://doi.org/10.1186/s12888-016-1019-y

[3]: Todd, T. P., Vurbic, D., & Bouton, M. E. (2014). Behavioral and neurobiological mechanisms of extinction in Pavlovian and instrumental learning. Neurobiology of learning and memory, 108, 52–64. https://doi.org/10.1016/j.nlm.2013.08.012

[4]: Rachman, S. J. (1989). The return of fear: Review and prospect. Clinical Psychology Review, 9(2), 147–168. https://doi.org/10.1016/0272-7358(89)90025-1

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