In the neurosurgery ward of the David Geffen School of Medicine at UCLA, Danny, a stocky 21-year-old college student wearing blue pajamas and sporting a wispy goatee, sits on a bed watching one photo after another flash by on a laptop screen. Several macho movie stars appear in rapid succession, including Arnold Schwarzenegger, Steven Seagal, Sylvester Stallone, and Mr. T, the Mohawked brawler who plays Stallone’s rival in the boxing film Rocky III. At first glance, one might guess that Danny has volunteered for a Hollywood survey: Who’s your favorite action hero? In fact, Danny is the real hero. The black cables emerging from the white turban wrapped around his skull hint at his role in investigating a truly profound question: How do thoughts form in the human brain?
Danny suffers from epilepsy, and he has had electrodes temporarily implanted into his brain to monitor seizures. Ideally, the electrodes will pinpoint the neural defect triggering his seizures so that the defect can be surgically removed. During the week or so that the electrodes remain in Danny’s brain, he has volunteered to participate in experiments aimed at understanding the underpinnings of cognition. Such research is quite rare; for obvious ethical reasons, neuroscientists have few opportunities to gather data from deep inside a living human brain.
This particular experiment touches on one of the most challenging puzzles of neuroscience: How do brain cells recognize items as complicated as a toaster oven, the number nine, a zebra, Bill Clinton, or the film character Rocky? Are single cells like transistors in a computer or pixels on a television screen, contributing just minute pieces of information that only when combined with the output of thousands or millions of other cells form the complex pattern that means Rocky? Or can a single neuron learn to recognize that face?
