Depressed people have trouble relating to other people—in part because they have trouble processing events and may think positive happenings are negative. That extends even to a diminished ability to understand the meaning of happy and sad facial expressions. A group of European researchers looked closer at this by watching people's brains while they looked at sad faces.

What the researchers wanted to know: What does your brain do when you look at a sad face? Does Prozac change that?

What they did: Nineteen patients with major depression and 19 healthy volunteers came in for fMRI sessions. fMRI, or functional magnetic resonance imaging, is a way to take a picture of the brain while it does something and see which parts of the brain light up. The areas that light up are the ones getting the most blood, which means they're the most active. Each person came in twice to look at sad faces, once for a baseline test and once at eight weeks; the depressed patients took fluoxetine hydrochloride (Prozac) between the two tests.

What they found: According to their brain scans, depressed patients responded more strongly to sad faces than healthy volunteers did at their first test, but the difference diminished after they'd taken eight weeks of Prozac. The researchers mapped the differences in the brain and found that Prozac reduced activity in the amygdala, an area of the brain that responds to facial expressions expressing emotions, including fear, sadness, and disgust.

What the study means to you: Well, it's hard to see the direct clinical use of this (unless it's to say that Prozac changes how your brain works, which we knew), but it does help scientists understand depression and the brain.

Caveats: It would have been better scientifically to compare the depressed patients on Prozac with depressed patients on a placebo, but it's ethically problematic to withhold drugs from sick patients.

Find out more: All about fluoxetine (Prozac) from MedlinePlus

A psychologist at the University of Western Ontario presents "fMRI for Dummies: A Reference for the Rest of Us Neuroscientists."

Functional MRI is also used for diagnostics; a website sponsored by two organizations of radiologists explains the procedure.

Read the article: Fu, C.H.Y. et al. "Attenuation of the Neural Response to Sad Faces in Major Depression by Antidepressant Treatment." Archives of General Psychiatry. September 2004, Vol. 61, pp. 877–889.

Abstract online: http://archpsyc.ama-assn.org