A woman in her early twenties sits alone in a small, windowless room at the University of Wisconsin's Health Emotions Research Institute in Madison. A bundle of spaghetti-thin wires draped over her head contains sensors that register the electrical activity of 128 brain sites as she watches photographic images flash by on a computer screen. A plump mushroom pops up for a few seconds, followed by a mangled body in a wrecked car and then a blooming rose.
Meanwhile, in a separate room, grad student Chris Larson watches the woman on a video screen and records the shifting pattern of electrical impulses in her brain. When a photo of a naked man and woman prompts a noticeable blip, Larson smiles. "Erotic pictures are the best," she says, for eliciting strong positive responses.
The electric charges Larson is most closely observing come from the woman’s prefrontal cortex, just behind her forehead. ...
