In a 19th-century painting, French doctor Philippe Pinel is shown breaking the chains encircling mentally ill patients at a French institution called Salpetriere, freeing them at last from their dank dungeons.

Before the work done by Pinel and a handful of other compassionate theoreticians, those with mental disorders were seen as morally weak, possessed by demons, even contagious. It was a dark era when mentally ill people -- presumed guilty of sinning against the gods -- were ostracized, physically abused or burned at the stake.

Some brain researchers, like Dr. Stuart C. Yudofsky of Baylor College of Medicine in Houston, draw a comparison between the mentally ill of Pinel's time and present-day sufferers from a variety of ills -- alcoholism, substance abuse, aggression and anti-social behaviors. Such people are viewed as morally weak, lazy, criminal, even evil.

The researchers predict that in years to come, through the illumination of brain science, the biological basis of many of these ills will be revealed. They say it will be the modern-day equivalent of Pinel unlocking the neck collars at Salpetriere, and no less controversial.

"If we now begin to reconceptualize substance abuse and violence disorders as having more of a brain basis, you can believe me, people will be upset," says Dr. Yudofsky, chairman of psychiatry and behavioral sciences at Baylor College of Medicine.

A leading researcher in neuropsychiatry who specializes in studies on the medical treatment of aggression, Mr. Yudofsky says some people will misinterpret the focus of neuropsychiatrists, believing their goal is to give criminals and drug addicts an easy way out through biology.

"My brain made me do it" will be the resulting refrain in courtrooms throughout the nation.

Dr. Yudofsky, however, says he believes "These people should be dealt with stringently, be made responsible for their actions, and society should be protected." But he says, too, that he is someone who believes in prevention. "Ask yourself, where do you want to spend your tax dollars? Early on, in research, detection and prevention? Or downstream in building prisons?"

The leading textbook on neuropsychiatry (co-edited, incidentally, by Dr. Yudofsky) reveals that 95 percent of what scientists know today about the brain as it relates to behavior has been discovered only in the past five years.

The field of neuropsychiatry arose in the 19th century but fell from prominence during the 20th century, as psychiatry became almost exclusively focused on the "psychodynamic" roots of behavior -- the effects of parenting, childhood experiences and so on, on the individual.

In recent years, however, a rejoining of neuropsychiatry to the fields of psychiatry and psychology has been seen.

Neuropsychiatrists treat patients with mental illnesses stemming from brain disorders -- injuries, conditions like Parkinson's disease, tumors, substance abuse. Their research puts them at the epicenter of the newest -- and usually controversial -- theories of human behavior, such as the current debate over the roots of homosexuality.

Trauma to the brain

Dr. Yudofsky and his colleagues base their "biopsychological" theories of aggression on studies in which animals whose brains are lesioned become violent, and on patients who have become aggressive after suffering strokes, head injuries or other assaults on the brain.

"We've known for a long time that when someone who has not been violent before suffers [injury] to certain regions of the brain, they can become extremely violent," Dr. Yudofsky says. "Now we are asking ourselves, are there individuals who by virtue of genetics or perhaps by injuries that happened early in life -- uterine trauma, childhood trauma, infections, malnutrition -- who are more prone to violence?"

Perhaps the most compelling evidence for a genetic basis for aggression stems from studies of twins. According to a 1988 study, twins reared both together and apart rated similarly 44 percent of the time on a personality scale testing for aggression. This is a "strong" indicator that biology plays a part, says Thomas J. Bourchard Jr., director of the Minnesota Center of Twin and Adoption Research.

Dr. Yudofsy admits that "there's no question that we can take a person with a normal brain and emotionally damage them by being abusive and cruel, and they will become violent." But there's more at work, he says.

"Before we discovered we could put two lenses together and create a microscope, the idea that particles too small to see could get into our systems and make us become run down and even die would have sounded like pure superstition. And yet that's exactly what happened when bacterial infection became subject to scientific study.

"It has been the same with many psychiatric disorders. The discovery of lithium to treat manic depression has . . . brought about the amelioration of untold human suffering."

Dr. Yudofsky and others are convinced that social disorders will also reveal themselves to be malleable to the healing touch of technology.

Dr. Yudofsky conjectures that in years to come researchers will discover that sociopathic behavior -- even human selfishness -- has some biological basis. Researchers are studying the organic roots of altruism -- the drive to help others, sometimes even at our own risk.

Inheriting only good traits?

He finds it interesting that people will accept the notion that good characteristics can be passed down -- an affinity for the violin, say, or athletic ability but not negative characteristics or temperaments.

Some charge, however, that biological theories of human behavior are rooted in racism. When one researcher in the '80s released a study on the possible organic basis of criminality in a group of prison inmates, who were predominantly minorities, he was branded a bigot.

Dr. Yudofsky insists his theories are not related to ethnicity or social class, but that brain dysfunction affects us all, directly or indirectly.

Others simply argue that it's a cop-out.

"It's easier to say something is wrong inside a person than it is to fix society," says Don Cherek, professor of psychiatry and behavioral science at the University of Texas Medical School.

He argues that aggression and addiction are learned, that environment overwhelmingly has the most profound effect on human behavior. He points to the fact that areas plagued by violence and drug abuse are also the ones plagued by poverty and neglect. Those who favor biological theories are intimidated by the overwhelming task of ridding America of poverty and providing equal opportunities in education, he says.

Dr. Yudofsky argues one cannot separate nature from nurture: They are indelibly intertwined. It's not either/or. It's both.

New findings in neuroscience

And, other researchers describe a future radically different from today -- a world in which alcoholics will take a pill to eliminate their craving for liquor, in which incredibly minute psychosurgery will excise the aggressive part of a criminal's brain while leaving personality intact, and in which convicts will undergo enforced medication instead of serving jail time.

What won't change, they insist, is the concept that human behavior is an amalgam of many things -- thoughts, experiences, drives, desires, goals -- and not just the random firing of genetically determined synapses.

"A brain lesion may predispose you to aggression, but it can't automatically make you decide to be aggressive. There is still a large element of choice and free will involved," says Jonathan Silver, associate professor of clinical psychiatry at Columbia University.