I'm lying in the plastic cocoon of an MRI machine, an instrument that measures activity in different parts of the brain. As I try to hold still, the loudly clanking machine runs a structural scan to locate the anterior cingulate cortex and the insula, regions involved in processing pain. A computer then translates the MRI signal into three small animated fires, representing the activity levels of the cingulate and the right and left insula, projected onto a screen above my face.

I concentrate to make those fires roar and ebb, using only my thoughts. As I do, the MRI is measuring changes in the blood flow to selected parts of my brain. The patterns of blood flow tell the computer how neural activity is changing. By trying to control the size of the fires, I am attempting to control brain activity in the cingulate and insula, and in turn to quell the chronic back pain that has irked me in recent years.