A study recently published in US-American Nature Neuroscience included 21 female patients who had been admitted to hospital for treatment of anorexia nervosa, and 21 healthy female control subjects. All study participants first had to evaluate the nutritional value and flavour of 76 food products. Based on this data, one low-fat and one high-fat reference food were randomly selected which had previously been classified as neutral. Subsequently, the women had to choose between the reference food and one of the other food products. During this process, the researchers tracked the brain activity of women via functional magnetic resonance imaging (fMRI). The day after the fMRI-examination it was then determined how many calories the women took in at a buffet, where they were able to eat the foods of their choice.
Unsurprisingly, it was found that women with anorexia nervosa significantly less frequently picked out high-fat foods than those chosen by the control group. Interestingly, this decision was associated with activity in the striatum – a brain region that plays a role in reinforcement learning as well as in action selection and control. In the anorexia patients the dorsal striatum in particular was significantly more active than in the control group. However, this increased activity was found only during the decision phase, but not at the stage of food evaluation. There were also differences in the interconnection between the dorsal striatum and the dorso-lateral prefrontal cortex (DLPFC): In healthy subjects, this was particularly marked when they were presented with fatty foods. Among patients with anorexia nervosa the opposite was able to be observed: low fat foods evoked a stronger interconnection than did fat rich foods. The more pronounced were the differences in the response to low-fat versus high fat food, the fewer calories the subjects took in the next day. This suggests that with anorexia nervosa the dorsal striatum virtually imposes its will on the DLPFC.
Other interconnection = different behaviour
The fact that the brain activity of people with anorexia nervosa differs from that of healthy people is not a new realisation. Previous studies have, for example, already been able to show [Paywall] that in anorexia patients differences in neural circuits are the reason that they are less strongly reactive to rewards and hunger as motivational drive for food. There are also indications that differences in taste perception lead to sensory overstimulation and thus contribute to anorexia-typical food avoidance behaviour. What’s new in the published study, however, is that researchers for the first time have put the process of decision-making under the fMRI microscope.
The results presented in the publication not only serve basic research in pathophysiology of anorexia nervosa but they also open up specific treatment options for practice. “We are already developing a new intervention process for use in psychotherapy, one which is based on the principles of habit reversal and enables the patients with anorexia nervosa to modify maladapted behaviours “, explains Dr. Joanna Steinglass, one of the lead authors. “While we continue to expand our understanding of the brain mechanisms, new therapeutic approaches for medications could emerge”.
Skinniness and other addictions
Although anorexia nervosa is a complex disease with many different forms, there are stereotypical behaviours which belong to it. These include, for example, that low calorie and low-fat foods are selected over a continuously long period of time. Until now, this behaviour was explained as being based on a pronounced ability to overcome primary instincts and to suppress physiological basic needs – anorexia nervosa is almost an expression of targeted self-control. This model nonetheless cannot explain why people continue to repeatedly make such maladaptive decisions, even when they know better and actually want to improve.
The now published work indicates that the decisions made by those affected are not subject to the free will (alone). The dorsal striatum, which apparently controls the eating choices in the anorexia patients, is part of the brain system that is involved in the habitual control of actions – and might be able to be shown to have connections to addictive behaviour. “This study may also help in placing anorexia nervosa alongside disorders such as substance abuse, gambling and other diseases in which decisions are involved which are influenced by excessive activity in the dorsal striatum”, explains study leader Dr. Daphna Shohamy from Mortimer B. Zuckerman Mind Brain Behavior Institute at Columbia University in New York. “Understanding how common neural circuits contribute to the decision making process in seemingly unrelated illnesses will allow researchers to focus on core disturbances and to achieve progress in the treatment of various diseases”.
Anorexia – just a bad habit?
The striatum plays a role both in the development of “normal” habitual behaviour as well as “abnormal” habits such as states of addiction. Moreover, it is significantly involved in procedural and implicit learning. Whereas the ventral striatum is apparently active in more immediate rewards, the dorsal striatum reacts to future rewards. In the formation of habit-driven behaviour as well as in the development of addictive behaviour, activity moves gradually from the ventral to the dorsal striatum. This correlates with the common theory that addiction develops over several steps: it starts with conscious, volitional consumption, from which a habitual abuse through repeated exposure evolves, and eventually ends up in a compulsive addiction which is no longer subject to free will.
Repetitive behaviours and thoughts are also typical of neuropsychiatric disorders such as Tourette-syndrome and obsessive-compulsive disorder, but also schizophrenia and Huntington’s – little wonder that these disorders are also associated with abnormal striatum activity . Whether in the case of anorexia nervosa habitual behaviour is, however, the cause, or merely an expression of the disease, remains in spite of studies an open question. But should anorexia actually turn out to be an addiction like drug addiction and gambling addiction, the question arises as to how much conscious control any such person actually has in his or her misguided (eating) decisions, and consequently how much responsibility can, should and must he or she assume in the responsibility for these decisions. At least the results of the now published study should help in making it clear that a mental illness such as anorexia nervosa cannot be disempowered through insight and willpower alone.