Melanie Thernstrom lies motionless inside the large, noisy bore of a functional MRI scanner at Stanford University. She tries to ignore the machine's loud whirring as she trains her attention on a screen mounted inside the scanner, right in front of her eyes. An image of a flame bobs and flickers, shifting subtly in size. To her, the flame is a representation of the searing pain in her neck and shoulder, with its fluctuations reflecting the rise and fall of her discomfort. To the neuroscientists scrutinizing her through a window from the control room next door, the flame is a measure of the activity in a part of her brain.