A century-and-a-half ago, a tape measure was an even more useful tool than it is now: You could use it to predict who was going to commit a crime.

That practice was part of the pseudoscience known as phrenology, which held that the shape and size of the head revealed the roots of a person’s behavior. And though those phrenologists have long since been discredited, had they possessed the ability to look at the deep structures of the brain, instead of the superficial bones and skin that surround it, they might have discovered the field of research we now know as neurocriminology.

Adrian Raine, a Penn Integrates Knowledge professor in the departments of criminology, psychiatry and psychology, is at the forefront of this field. His work broadly attempts to connect criminal, psychopathic and aggressive behavior to physical characteristics of the brain, an area of study that has profound implications for our notions of responsibility and guilt.

Though the idea of ceding total control of one’s actions to quirks of brain structure is disturbing—Raine calls it a “slippery slope to Armageddon”—it’s impossible to deny that the brain plays some role in an individual’s personality, decision-making and ability to interact with others.

Raine, who previously worked as a prison psychologist in his native England, feels that understanding the connections between brain abnormalities and antisocial or criminal behavior is necessary to develop effective interventions. If a developmental disorder will a cause a child to have more difficulty controlling aggressive impulses as an adult, society should try to take measures—be they social, economic or medical—to help alleviate this disadvantage, he says.

Such a plan would rely on early detection of children who are at risk. In his most ambitious project, Raine and his colleagues measured autonomic fear conditioning—where the anticipation of a punishment causes an involuntary physical response that can be measured on the skin—in 1,800 children. They searched for their subjects’ court records 20 years later. After controlling for social factors, they found that poor fear conditioning in 3 year olds increased their odds of becoming a criminal offender by age 23.

Structural impairments in the brain also appear to be in place early in life in offenders. Adults with cavum septum pellucidum—a neurological condition that reflects underdevelopment of the emotion limbic system before the first six months of life—have higher rates of psychopathy, antisocial personality disorder, arrests and convictions.

Raine and his colleagues have demonstrated that adult psychopaths have an amygdala that is 18 percent smaller in size compared to normal controls. The amygdala is part of the brain’s limbic system that is critical for emotion, especially for fear conditioning.

Psychopaths also showed lower activity in the amygdala when confronted with moral dilemmas as compared to controls. Raine says this suggests that “psychopaths know right from wrong, but they do not have the feeling of what is right and what is wrong.”

But, Raine says, not all offenders are the same. In a study of spouse abusers, Raine and colleagues demonstrated that when presented with emotionally provocative stimuli, wife abusers showed greater activity in the amygdala, an area that helps generate emotions, and less activity in the prefrontal cortex, which helps regulate emotions, as compared to non-abusers.

Raine’s newest research also shows the complexity inherent in trying to connect activity in the brain with certain types of crime. A pilot study, currently being conducted with William Laufer, professor of legal studies and business ethics, sociology, and criminology in the Wharton School, is probing the brains of white-collar criminals. Raine says this early research reveals these offenders show better decision-making and increased attention. Offenders also show an enlargement in areas of the brain responsible for social information processing, emotion regulation and the monitoring of abstract rewards like money, as compared to carefully matched controls. Raine cautions that this work is very provisional and must be treated with appropriate circumspection.

While neurocriminology has come a long way from the days of measuring murderers’ skull circumferences, it still raises fundamental questions about how justice systems should operate. As Raine puts it: “If offenders have brain dysfunction for reasons beyond their control, should they be held fully responsible for their crimes?”