Anorexics are 'wired' differently

Monday December 17 2007

“Anorexia is caused by a ‘faulty wiring’ of victims’ brains – not size zero models”, The Sun and other newspapers reported today.

The Times said: “Brains of anorexia sufferers behave differently to those of the rest of the population and certain people are born with a susceptibility to develop the condition”.

The papers were reporting on research conducted in the US that showed that the brains of women who had recovered from anorexia behaved differently during a “computer game” where the players were rewarded if they guessed correctly.

The study behind these stories highlights the differences in the brain’s responses to “wins” and “losses” in women who had recovered from anorexia. However, only 13 women were studied and they all had one particular type of anorexia. This should be taken into account before assuming the results would apply to a wider group of people with anorexia. The study design also means that it is not possible to tell if the brain differences contribute to the onset of anorexia, or if they are a consequence of having had the condition.

The newspapers may have oversimplified their interpretation of this research. Even if there are found to be biological differences in the brains of people with the condition, anorexia remains a psychiatric disorder with a host of complex causal factors. It is too simple to suggest that only one factor, whether it is images of supermodels or “the way the brain operates”, causes the condition.

Where did the story come from?

Dr Lorie Fischer and colleagues from the University of Pittsburgh and other medical and academic institutions in the USA and Germany carried out the research. The study was funded by the National Institute of Mental Health. It was published in the peer-reviewed American Journal of Psychiatry.

What kind of scientific study was this?

This cross sectional study compared the responses to a “guessing game”, of women who had recovered from anorexia (the limiting type where restricting food intake is the primary means of weight loss) to women with no history of anorexia.

The researchers recruited 13 women who had recovered from anorexia (having regained a normal eating behaviour, kept a body weight that was at least 85% of the average body weight and begun having normal periods again), and 13 “control” women of the same age who were healthy and had been within the normal weight range since their first period. All the participants had their anxiety levels, lifetime psychiatric history and other demographic information measured and captured.

The participants then completed a task on a computer called the “guessing game paradigm”, which involved looking at pictures of playing cards on a screen and guessing whether a concealed number on the opposite side of the playing card was greater or less than five. Participants won $2 for a correct guess, and lost $1 for an incorrect guess or 50c if they failed to guess in time. The women used a handheld controller to select their responses and were informed on the screen whether they had “won” or “lost” each guess. All the participants repeated the test 26 times.

While undertaking the tasks, MRI (magnetic resonance imaging) was used to scan the brains of the participants. The researchers focused on a region of the brain called the caudate and ventral striatal regions, which other studies have identified as being involved in processing this sort of task. The two groups were compared for their performance at the task (e.g. time to guessing, whether the guess was correct etc) and how their brains responded to the rewards and losses associated with the guessing game. The researchers used “functional MRI”, a technique that reveals the areas of increased blood flow within the brain that occur as a response to a stimulus; in this case the questions or activity of the subject.

What were the results of the study?

There was no difference between the groups in the time taken to make a guess or on the type of guess. The MRI showed that in both groups the caudate region of the brain showed a differential response to the “win” and “lose” guesses.

However, differences between the two groups were evident in that the recovered anorexia group had a greater response in the caudate region than the control group. The control group meanwhile exhibited a differential response between the wins and losses in the ventral striatum region of the brain whereas the recovered anorexia group did not.

Other differences included:

  • a differential response to wins and losses in a region of the brain (from the subgenal cingulate into the ventral striatum) in the control group;
  • a differential response in a different region (middle and dorsal striatum) in the recovered anorexia group;
  • seemingly a greater early response to losses in the recovered women compared to the control women;
  • within the posterior cingulate region of the brain, the control women had a more sustained response to the wins while in the left parietal cortex the recovered women had a greater response to wins; and
  • the level of response in the left caudate region in recovered women was linked to the severity of their level of anxiety.

What interpretations did the researchers draw from these results?

The researchers conclude that their study shows that people who have recovered from anorexia have altered patterns of response to positive and negative feedback in particular regions of their brains.

They say that this suggests that people with anorexia may have “difficulty discriminating between positive and negative feedback, relative to healthy comparison subjects”.

The regions of the brain concerned with “planning and consequences” seem to be activated in people who have recovered from anorexia which may correlate with a behavioural trend to worry obsessively about the consequences of certain actions.

What does the NHS Knowledge Service make of this study?

When interpreting this study’s findings, several points should be kept in mind:

  • It is a small study that compared only 13 women who had recovered from anorexia to 13 healthy control women. As such, the results cannot be automatically applied to all women with anorexia. In addition, the women had all recovered from a particular type of anorexia (the limiting type) and as such the findings may not apply to people who have or have recovered from the binge/purging type of anorexia.
  • Because of the study design, (i.e. cross sectional), it is not possible to conclude that the brain differences caused the anorexia. The women’s experience of anorexia may have changed their response to positive and negative stimuli. Studies with “prospective” designs, (i.e. following women over time) would better address this question.
  • The study’s findings contribute to an understanding of why people who have had anorexia are able to “sustain self-denial of food and other life comforts and pleasures”, however as the researchers themselves admit, they cannot establish “whether these findings are a trait that contributes to the onset of anorexia nervosa or a ‘scar’ that is the consequence of past malnutrition and weight loss”.

Anorexia nervosa is a psychiatric condition resulting from complex psychological, genetic, and environmental factors. Ideas that single factors  - such as images of supermodels - can “cause” anorexia are unhelpful. Similarly, this study does not dispel the idea that any societal pressure to be thin might also act as a trigger or contribute to developing anorexia.

Analysis by Bazian
Edited by NHS Choices