This Is Your Brain On God

John Barry: The doctor asks the nun to begin her centering prayer. It's a Catholic method of prayer, goes back to the 14th century, a form of deep meditation. The nun sits straight, in silence. She closes her eyes and focuses on a sacred word, or small prayer. She "rests in God."

A catheter dangles from her arm. After 45 minutes, the doctor injects her with a radioactive tracer. He lets her pray 10 more minutes as the tracer in her bloodstream wends its way through her brain.

Then he leads the nun into his lab, has her lie down, and scans her brain. He's using a process called single photon emission computed tomography, or SPECT. It's a common technique in nuclear medicine, used to photograph the brains of patients suffering anything from seizures to brain trauma to heart disease to Alzheimer's.

The nun isn't sick. She's "on God."