Hey, it's Flora Lichtenen, and you're listening to Science Friday. Today in the show, despite

major advances in understanding the biology of mental health disorders, there's no blood test or brain

scan that will confirm if you have depression, anxiety, PTSD, or other psychiatric illnesses.

And yet, the next version of our Diagnostic Bible, the DSM, the Diagnostic and Statistical

Manual of Mental Disorders, will include biomarkers. So how close are we to pinpointing

the biological markers of mental illness? And what does that mean for diagnosis?

It's complicated. Here to untangle some of the science for us is Dr. John Crystal, professor of

psychiatry, neuroscience, and psychology at the Yale School of Medicine based in New Haven, Connecticut.

John, thanks for being here. Well, my pleasure, Flore. Okay. John, how hard is this problem, the biomarker for mental illness problem?

It's an enormously challenging problem.

You know, some people say that the brain is the most complicated structure in the universe.

And we're trying to decipher the codes that underlie the symptoms and challenges

that people experience in their lives. And therefore, it's an enormously challenging problem

that we've been working on for a long time. Well, why is defining biomarkers for mental illness

so difficult compared to other illnesses?

Well, one of the reasons is because we are usually not analyzing the exact tissue that we're

interested in. In other words, if you have a tumor, they would do a biopsy and analyze your cells to find out

exactly what the molecular signatures of your illness are.

And that helps to make sure that you get the treatment that you individually need.

That's what we'd like to go for in psychiatry to apply something that people call

precision medicine. But we have to do that without sampling your brain tissue because you probably

don't want us to do that. I mean, if you could sample brain tissue, would you be able to pick out

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