Bit by bit, that wondrous entity, the human personality, is being decoded. An even temper or a short fuse, an affectionate nature or a penchant for anonymous sex, a love of thrills or a tendency to withdraw: such elements of our cherished sense of self are being revealed as less the shadings of the soul than the manifestations of neurobiology.

In some cases, we've uncovered the chemistry of personality by changing it. Consider the architect who takes Prozac for depression and finds that not only are his symptoms gone, but so is a lifelong passion for hardcore porn. "The medication redefined what was essential and what was contingent about his own personality," writes his psychiatrist Peter Kramer in Listening to Prozac. Or consider the hyperactive child who takes Ritalin and discovers that now other kids will play with him. Social acceptance in a pill. Shyness, too, may succumb to a chemical cure. Research suggests that 1 in 5 babies is predisposed to be timid because of hypersensitivity of the amygdala--a small structure in the brain. Fixing such problems may sound like better living through chemistry, but it rattles the very bedrock of identity.

Now comes the most startling discovery yet. According to a recent report in Science, researchers have found discrete locations in the brain of an intricate system that serves, among other things, as the human moral compass. Largely in the prefrontal cortex, it is where reason is applied to complex social situations, where our personal scales of justice do their weighing. It may come as a shock that this highest, most spiritual faculty is just as identifiable and in some ways as physically vulnerable as, say, a knee joint. But vulnerable it is. One's moral fiber can literally snap. For it was just such a rupture that led the researchers to their discovery.

Neuroscientists Antonio and Hanna Damasio and three collaborators analyzed the battered 170-year-old skull of one Phineas Gage, whose cranium had been preserved as an object of medical fascination. Gage was a reliable fellow, well regarded by his workmates on the Rutland and Burlington Railroad. But on Sept. 13, 1848, while using explosives to prepare Vermont's craggy terrain for track, he suffered a hideous accident. Briefly distracted, the 25-year-old foreman triggered a premature explosion that launched a pointed iron rod, thick as a broomstick, right through his skull. The rod rocketed through his face, excising his left eye, and exited skyward through the top of his head. Astoundingly, Gage was able to stand and speak in a few minutes. His intelligence was intact. But later it became clear that the once upright young man had been altered. He now cursed, lied and behaved so abominably that he could not hang on to a job or a friend. The balance "between his intellectual faculty and his animal propensities" had been destroyed, wrote Gage's doctor, John Harlow. Gage was no longer Gage.

Gage's tale is dramatic, but given the physical presence of a moral faculty in the brain, it need not take an iron projectile to reshape one's ethics. How about a virus? A birth injury? A genetic defect? It is quite possible that some of history's greatest villains harbored an unseen wound much like Gage's in the prefrontal cortex. Such may be the condition of all psychopaths. This is not to say that experience has no relevance to character. Abuse during childhood, experience of all sorts is inscribed on the brain. But childhood traumas have never fully explained the psychopath, says Dr. Solomon Snyder, director of neuroscience at Johns Hopkins Medical School. "It's not as though these people weren't disciplined by their parents or didn't go to church. They can think rationally, but the moral judgment is lacking. It's as if there's a hole in the moral part of their brain."

And now, thanks to Phineas Gage, scientists will know where to search for that hole. It is surely where they will look when studying the brain--donated to science--of serial killer John Wayne Gacy, executed last May in Illinois. Suppose a Gage-like defect is found? Will it seem fair to have executed the man if he was physically incapable of moral judgment? As science begins to unravel bits of personality, accountability unravels with it. The person becomes his parts--some working, some defective through no fault of his own. Will it become incumbent upon society to submit all killers to a brain scan? Would that not be fairer than having psychiatrists battle in court over the merits of an insanity plea?

If moral judgment can be broken, surely the next step is to fix it. "If the abnormality is in a discrete part of the brain that uses a specific neurotransmitter, we could develop a drug treatment," suggests Dr. Snyder. It might even be possible to devise exercises to fortify wayward judgment, just as a stroke patient can benefit from occupational therapy. Another possibility: a prenatal test--abort the psychopath.

Medicine in the 21st century holds much promise. It offers a shot at cheering the despondent, repairing the unpopular, perhaps even doing the job of religion--correcting moral defects. This may seem like a good idea when pondering the likes of John Wayne Gacy. But when we put the human soul on the operating table, we had better watch where we cut. Any one of us could be better than we are, but who's to say who needs fixing?

Copyright (c) TIME Magazine, 1995 TIME Inc. Magazine Company; (c) 1995 Compact Publishing, Inc.

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