If you're at risk for heart disease, doctors can monitor your cholesterol. But psychiatrists don't have an analogous test for mental illnesses. That may change with a new discovery: Scientists have pinpointed a small spot in the brain that has a 71% chance of predicting whether high-risk patients will develop schizophrenia.
About 75% of diagnosed schizophrenics show early, fleeting signs of the disease before they fully develop it. These so-called prodromal symptoms include mild hallucinations, such as hearing your name in the wind, or a sudden, unfounded suspicion that your friends are talking about you behind your back. Some patients may even experience a full psychotic episode--similar to what schizophrenics experience chronically--which lasts only a couple of days. Not all prodromal patients develop psychotic disorders: Two-and-a-half years after first experiencing these symptoms, only 35% receive a schizophrenia diagnosis. Predicting who gets that diagnosis is "a little better than flipping a coin," says Scott Schobel, a psychiatrist at Columbia University.
Schizophrenia marker. Schizophrenics and patients who later develop the illness (right and center) have higher resting activity levels (red) in the CA1 subfield of the hippocampus than do healthy subjects (left).
To help understand how these patients progress from mild hallucinations to schizophrenia, Schobel and his colleagues compared brain activity between 18 schizophrenic and 18 healthy patients. The scientists used a high-resolution version of functional magnetic resonance imaging, which measures brain activity through changes in blood volume, to take detailed snapshots of the subjects' brains while they lay in the scanner.
Three regions differed: two in the frontal cortex and a 5-millimeter-long part of the hippocampus called the CA1 subfield. The hippocampus, the brain's learning and memory center, is known to be more active in schizophrenics, but this study, which appears in this month's issue of Archives of General Psychiatry, pinpoints the part that's hyperactive. Moreover, the researchers found that among schizophrenics, those with a busier CA1 had worse delusions.
The team next scanned 18 patients with prodromal symptoms and then followed up with them every 3 months for 2 years to evaluate whether their symptoms had worsened. Seven patients eventually developed full-blown psychotic disorders. When the researchers compared these patients' earlier brain scans with those of the other 11 prodromal patients, the only difference in activity was in the CA1 subfield--these seven patients had a 50% greater level of CA1 activity than the others did. Using these measurements, the researchers could retroactively predict 71% of the patients who went on to develop psychosis.
Even if activity in the CA1 subfield proves to be a diagnostic for schizophrenia, Schobel notes that it would only be useful for patients with an elevated risk. "The appropriate analogy would be a patient who already has a known family history of heart disease and they're complaining about chest pain," he says.
The study brings scientists one step closer to a diagnostic marker for schizophrenia, says Paul Thompson, a neuroscientist at the University of California, Los Angeles. Although larger studies are needed to confirm the results, psychiatrist Kristin Cadenhead of the University of California, San Diego, says that "even small studies are important at this point." Thompson and Cadenhead believe that doctors testing new drugs to treat schizophrenia could use a decrease in CA1 activity as a measure of a treatment's effectiveness.
By Michael Torrice
ScienceNOW Daily News
8 September 2009
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