They seem almost alive: snapshots of the living human brain. Not long ago, scientists predicted that these images, produced by sophisticated brain-scanning techniques, would help cut through the mystery of mental illness, revealing clear brain abnormalities and allowing doctors to better diagnose and treat a wide variety of disorders. And nearly every week, it seems, imaging researchers announce another finding, a potential key to understanding depression, attention deficit disorder, anxiety.
Yet for a variety of reasons, the hopes and claims for brain imaging in psychiatry have far outpaced the science, experts say.
After almost 30 years, researchers have not developed any standardised tool for diagnosing or treating psychiatric disorders based on imaging studies.
Several promising lines of research are under way. But imaging technology has not lived up to the hopes invested in it in the 1990s ' labelled the ‘Decade of the Brain’ by the American Psychiatric Association ' when many scientists believed that brain scans would turn on the lights in what had been a locked black box.
Now, with imaging studies being published at a rate of more than 500 a year, and commercial imaging clinics opening in some parts of the US, some experts say that the technology has been oversold as a psychiatric tool. Other researchers remain optimistic, but they wonder what the data add up to, and whether it is time for the field to rethink its approach and its expectations.
“I have been waiting for my work in the lab to affect my job on the weekend, when I practice as a child psychiatrist,” said Dr Jay Giedd, chief of brain imaging in the child psychiatry branch at the National Institute of Mental Health, who has done MRI scans in children Monday through Friday for 14 years. “It hasn’t happened. In this field, every year you hear, ‘Oh, it’s more complicated than we thought.’ Well, you hear that for 10 years, and you start to see a pattern.”
Psychiatrists still consider imaging technologies like MRI, for magnetic resonance imaging, and PET, for positron emission topography, to be crucial research tools. And the scanning technologies are invaluable as a way to detect physical problems like head trauma, seizure activity or tumours. Moreover, the experts point out, progress in psychiatry is by its nature painstakingly slow, and decades of groundwork typically precede any real advances.
But there is a growing sense that brain scan research is still years away from providing psychiatry with anything like the kind of clear tests for mental illness that were hoped for. “I think that, with some notable exceptions, the community of scientists was excessively optimistic about how quickly imaging would have an impact on psychiatry,” said Dr Steven Hyman, a professor of neurobiology at Harvard and the former director of the National Institute of Mental Health. “In their enthusiasm, people forgot that the human brain is the most complex object in the history of human inquiry, and it’s not at all easy to see what’s going wrong.”
For one thing, brains are as variable as personalities. In a range of studies, researchers have found that people with schizophrenia suffer a progressive loss of their brain cells: A 20-year-old who develops the disorder, for example, might lose 5 per cent to 10 per cent of overall brain volume over the next decade, studies suggest. Ten per cent is a lot, and losses of volume in the frontal lobes are associated with measurable impairment in schizophrenia, psychiatrists have found. But brain volume varies by at least 10 per cent from person to person, so volume scans of patients by themselves cannot tell who is sick, the experts say.
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Studies using brain scans to measure levels of brain activity often suffer from the same problem: What looks like a “hot spot” of activity change in one person’s brain may be a normal change in someone else’s. “The differences observed are not in and of themselves outside the range of variation seen in the normal population,” said Dr Jeffrey Lieberman, chairman of the psychiatry department at Columbia University Medical Center and director of the New York State Psychiatric Institute.
Most fundamentally, research has not answered the underlying question that the technology itself has raised: Which comes first, the disease or the apparent difference in brain structure or function that is being observed' For a definitive answer, experts would have to follow thousands of people from childhood through adulthood, taking brain scans regularly, and matching them with scans from peers who did not develop a disorder.
In a series of studies of people with severe depression, Dr Helen Mayberg, a professor of psychiatry at Emory University in Atlanta, found a baffling pattern of activity. Using PET scanning technology, Mayberg found sharp dips and spikes of activity in about six areas of these patients’ brains as their moods improved while they were taking either antidepressant drugs or placebos. The changes were similar in all patients, but it was difficult to tell how the scattering of the dips and spikes were related.
At the Brainwaves Neuroimaging Clinic in Houston, doctors use the scans to diagnose and choose treatment for a range of psychiatric problems, according to a clinic spokeswoman. And a variety of doctors advertise the imaging services, particularly for attention-deficit disorder, on the Internet. But the experts who study imaging and psychiatry say there is no evidence that a brain scan adds significantly to standard individual psychiatric exams.
Imaging researchers are also studying depression-related circuits to see how they may arise from genetic variations known to put people at risk for depression. And as always, the technology itself is improving: A new generation of MRI scanners, with double the resolution power of the current machines, is becoming more widely available, Lieberman said.
“With increased resolution, we’ll be able to do more sensitive and more precise work, and I would not be surprised if anatomy alone based on volume will be a diagnostic feature,” he said. “We have gained an enormous amount knowledge from thousands of imaging studies, we are on the threshold of applying that knowledge, and now it’s a matter of getting over the threshold.” But for now, neither he nor anyone else can say when that will happen.