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Great thinkers have had no shortage of ideas on the subject. Plato was convinced that the mind must be located inside the head, because the head is shaped more or less like a sphere, his idea of the highest geometrical form. Aristotle insisted that the mind was in the heart. His reasoning: warmth implies vitality; the blood is warm; the heart pumps the blood. By the Middle Ages, though, pretty much everyone agreed that the mind arose from the brain -- but still had no clear idea how it arose. Finally, in the 17th century, the French philosopher Rena Descartes declared that the mind, while it might live in the brain, was a nonmaterial thing, entirely separate from the physical tissues found inside the head. Furthermore, said Descartes in one of history's most memorable sound bites, "Cogito, ergo sum" (I think, therefore I am). His point: consciousness is the only sure evidence that we actually exist.
Until just a few years ago, unraveling the relationship of mind and brain was beyond the realm of observation and experimentation. But science has finally begun to catch up with philosophy. Using sensitive electrodes inserted deep into the gray matter of test animals, researchers have watched vision as it percolates inward from the eye's retina to the inner brain. Powerful technologies such as magnetic resonance imaging (mri) and positron-emission tomography (PET) have also provided a window on the human brain, letting scientists watch a thought taking place, see the red glow of fear erupting from the structure known as the amygdala, or note the telltale firing of neurons as a long-buried memory is reconstructed. "What's so exciting," says Patricia Churchland, a professor at the University of California at San Diego, "is that the philosophical questions raised by the Greeks are coming within the province of science."
In response to this enormous opportunity -- not just to clarify the mysteries of consciousness but also to understand and treat such devastating mind malfunctions as Alzheimer's disease, depression, drug addiction, schizophrenia and traumatic brain damage -- research projects have multiplied dramatically. Over the past several years, Johns Hopkins has launched the Zanvyl Kreiger Mind/Brain Institute and Harvard has created the Mind/Brain/Behavior Initiative. And at the urging of the National Institute of Mental Health and other organizations, President Bush declared the 1990s the Decade of the Brain.
In short, the brain is a hot topic, and while a complete understanding of its inner workings will be a long time coming, the surge of interest in things cerebral has already produced tantalizing results. It turns out that the phenomenon of mind, of consciousness, is much more complex, though also more amenable to scientific investigation, than anyone suspected. Descartes was right in one sense: the mind is not a physical object, and while it exists within the brain, it has no particular location. The destruction of any given part of the brain can severely alter the mind in one way or another but not destroy it.