"Sometimes I think we are more explorers of an unknown continent that we are physicians or scientists," Torsten N. Wiesel, Winthrop Professor of Neurobiology, says quietly. That continent is the brain, and the 22 years of research Wiesel calls only the "first steps" in its exploration have won him and colleague David H. Hubel, Berry Professor of Neurobiology, the 1981 Nobel Prize for Medicine.

A research team since 1959, Hubel and Wiesel have studied the workings of the cerebral cortex's visual region, only a small part of the organ Wiesel terms "the most complicated machine on earth."

Yet Hubel and Wiesel's knowledge of the way the brain processes information from the eye advances the study of the full cortex--10 billion neurons folded together at the brain's crust that may be the key to man's development over other animals.

The goal is to understand how images from the eye are translated in the visual cortex to the language of the brain, Hubel says. The dream is to map the machinery of the mind.

"I have always believed that psychology must be a branch of biology," he says, "though some psychologists would disagree with me. The 'mind' is merely an abstraction," while the brain--in some biologically definable way-- comprises human thought.

In search of what they call the "neural substrate," the two researchers began implanting sensitive electrodes into the brains of anesthetized monkeys. The electrodes monitored individual cell responses from within the visual cortex; in a laborious process, Hubel and Wiesel tested the reaction of specific cells in specific areas of the visual cortex to the specific images placed before a monkey's eyes.

The apparatus was simply a slide show for the anesthetized monkeys. The knowledge of which cells would send out electrical impulses in response to--or "recognition" of--which visual patterns could offer a map of the architecture of the visual cortex.

The breakthrough came in what both Hubel and Wiesel say was an accident. The cells of the monkey's visual cortex failed to "recognize" white dots on the screen, but reacted regularly while the researchers were changing slides. "It wasn't the dot at all, but the edge of the glass" on moving slides, Hubel says.

The team took months to convince themselves that edges and lines caused the reactions in the cells. A newspaper or television picture is made up of tiny dots. But Hubel and Wiesel found that the visual cortex breaks objects down, not into dots, but into line segments.

As the mapping process continued, now with slides of lines and bars, the two discovered that different cells within the region are specialized, recognizing only certain images. Certain cells responded optimally to a bar or edge of light with a particular orientation along the visual axis. And more complex cells seemed to recognize more complex images passed on by several simpler cells.

"Each of these cells in the cortex is looking out of a pinhole to the world," Wiesel says, "only at later stages combining into a whole."

And while cells on either side of the brain responded preferentially to one eye over the other, more than half received input from both eyes. The upshot was a neurological sense of how and where the two separate retinal images are unified in the brain.

The overall primary visual cortex, Hubel and Wiesel discovered, is composed of two systems of columns. One groups together cells recognizing steadily changing angles of orientation of bars and edges, while the other holds cells with the same eye preference. This architecture has since been found all along the cortex, even in areas having functions which are still unknown.

"All this wasn't just a mysterious current moving through the brain," Wiesel says, "but a very, very precisely wired machine."

Though it is a vision that might disturb some, Hubel welcomes it. "A lot of philosophical questions can be bypassed," Hubel says. Terms like "the mind" or "free will," he adds, are "not valuable in the context of science."