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Psychiatry Newsletter - Desire, Pixellated
Hopkins Brain Wise Spring 2009
Date: March 11, 2009
Two young women of similar age and education undergo separate sessions in an MRI scanner. For both, the words bacon and later, celery flash before them. But there the similarities end: One woman finishes, saying, “I’m hungry.” The other, however, reports a rising sense of anger and rage at the first word, peace and calm at the second.
“We’ve long approached eating disorders with a focus on the meaning of patients’ behaviors,” says psychiatrist Graham Redgrave. An example might be young women saying a need for control underlies their binging and purging. But newer studies, he says, examine the behaviors themselves.
“We see them as motivated by something fundamental in the brain,” he explains. They could stem, in part, from a genetically paved predisposition to slip into certain circuits, from hormonal differences or a number of things biological—all with environment involved and none, as yet, confirmed.
In a field where therapy has come from trial and error, the push now is to understand eating disorders’ basic science. So Redgrave hopes first to confirm the affected brain areas. His most recent study, for example, aims to map the seat of the two desires that consume people with anorexia nervosa: wanting to be thin and wanting not to be fat. Though this work is very much a pilot study with its six patients and six controls, the results are interesting, he says; and are driving more work.
But how do you translate desire accurately into an image? Today, functional MRI images brain activity in a way not possible a decade ago. Yet imaging what’s meaningful is fraught with problems: Thoughts around food are complex. They often trail clouds of confounding personal memories. Birthday cake. Brussel sprouts. To try to get at the core, then, Redgrave turned to the Stroop task. Devised in the 1930s, it involves a simple activity that requires attention. Show test-takers the word red printed in blue and ask that they select the blue push-button from four others. Measure how quickly. Vary the colors and words.
The value in the Stroop is that words with emotional significance cause people to pause a heartbeat before pushing the button; it’s a nice, quantifiable property called the Stroop effect. While they were in the MRI scanner, both long-term anorexia nervosa patients and controls viewed colored, potentially loaded words such as gaunt or burger interspersed with neutral nouns like stapler or, more simply, four Xs.
A clear Stroop effect surfaced only for patients. And the resulting images revealed two brain sites of interest. One, active in patients seeing the “thin” words, is an area used in language, craving and task-planning. A second distinct planning area was active only in the controls when they viewed “fat” words.
“Drawing conclusions isn’t always wise in a small study,” says Redgrave, “but one possible idea is that food matters more to healthy people and thinness matters more to patients.”
If broader studies show that the brain area holds true for very ill patients, more work could show if activity there fades with treatment. Eventually, says Redgrave, we may be able to tell who does best with a therapy—a holy grail of sorts in his field.