Using MRI spectroscopy, Port can measure levels of chemicals such as n-acetyl aspartate, which is found only in neurons, or glutamate, which stimulates nerve-cell activity. When Port used the technique across many areas of the brain in bipolar patients and compared the results to those from healthy controls, he came up with a chemical fingerprint that seemed to be an indicator of bipolar disorder.

"When we compared all the bipolar patients in any mood state with their matched normal control subjects, we found that two areas of the brain were significantly different," Port says. Port and his team also identified changes in many regions of the brains of people with bipolar disorder that indicated whether they were in a manic state or depressed. "We found a chemical measure of the mood state," he says.

So has Port found the long-sought diagnostic test for bipolar disorder? Does his chemical fingerprint reliably identify people who have bipolar disorder and exclude those who don't?

Maybe, but he can't be sure yet. "We think we're on to something good," he says, but "we have to check it and make sure it will be clinically useful." It's a question of trying the technique with enough patients to be sure that it is statistically valid -- that it won't produce too many false positives or false negatives. It doesn't have to be perfect, but it has to be good enough to add useful information to what psychiatrists can discern through their traditional methods of diagnosis, interviews, and analyses of patient histories.

If Port is correct, however, and the technique proves itself, it would be a landmark in psychiatric research: a diagnostic test for bipolar disorder. And if the technique works with bipolar disorder, it could be adaptable to other psychiatric illnesses.

Port and others are also experimenting with diffusion tensor imaging. DTI measures water diffusion in the brain. Water flows through the brain as it does anywhere else -- along the path of least resistance. In the brain, that's along the axons, the neurons' long tails, which convey electrical signals to other neurons. (It's from the fatty, white insulation that surrounds most axons that "white matter" takes its name; the rest of the neuron, and uninsulated axons, together constitute "gray matter.")

Port is just beginning to research the technique. But eventually researchers will be able to use "DTI clinically to look for diseases that interfere with white matter -- amyotrophic lateral sclerosis [Lou Gehrig's disease] and schizophrenia," Port says.