Research Links Brain Damage & Violent Crime -- USC Studies Point To Underlying Causes Of Violent Crime In Young Offenders

But it appears to take the added complication of specific forms of maternal rejection to predispose a perinatally brain-injured youth to violence, according to another study in the current (September) issue of the American Journal of Psychiatry.

"It's becoming increasingly clear that we're never going to solve the problem of violent crime if we don't address the link between brain damage and criminal behavior," says University of Southern California researcher Adrian Raine, Ph.D., who directed both studies.  "Better prenatal, perinatal and postnatal care and better support for inadequate parents now appear to be the most promising forms of intervention."

For the Biological Psychiatry study, Dr. Raine directed scientists at USC and the University of California at Irvine as they used positron emission tomography (PET) to scan the brains of 41 murderers who had pleaded not guilty by reason of insanity.  The scientists also scanned the brains of 41 control subjects matched for known mental disorders and for age and gender.  Mental disorders among the subjects included schizophrenia, organic brain damage and a history of head injury.

PET scans measure the uptake of blood sugar (glucose) in various brain areas during the performance of simple, repetitive tasks.  (Glucose is the basic fuel that powers most cell functions.  The amount used is directly related to the amount of cell activity.)

On average, the murderers showed significantly lower rates of glucose uptake in three areas of the brain -- the prefrontal cortex, the corpus callosum and the posterior parietal cortex.  Their rates were 4, 18 and 4 percentage points lower, respectively, than the rates measured in control subjects performing the same tasks.

When the researchers compared the brain's two hemispheres for glucose uptake rates, they found that murderers consistently showed weaker activity in the amygdala and the hippocampus of the brain's left -- or more rational -- hemisphere.  These glucose uptake rates were each 4 percentage points lower than the rates measured in control subjects performing the same tasks.

But the murderers showed stronger activity in the thalamus, the amygdala, and the hippocampus of the right -- or more emotional -- hemisphere.  These glucose uptake rates were 6, 6 and 3 percentage points higher, respectively, than the rates measured in control subjects performing the same tasks.

€ The prefrontal cortex is involved in the inhibition of aggressive behavior. Studies have shown that damage to the region correlates with impulsiveness and unpredictable, uncontrolled actions.

€ The corpus callosum acts as a sort of computer modem, communicating information between the brain's left hemisphere, which is associated with reason and language, and the brain's right hemisphere, which is associated with emotion.

€ The posterior parietal cortex is involved in the integration of sensory input and the formation of abstract concepts.  Reduced glucose uptake in a portion of this region (the left angular gyrus) has been correlated with reduced verbal ability, while damage has been linked to deficits in reading and arithmetic.  Violent offenders have consistently been shown to do worse in school than their law-abiding peers.

€ The thalamus, the amygdala and the hippocampus are among the principal regions comprising the brain's limbic system -- a complex system of nerve pathways and networks.  The thalamus relays impulses from the amygdala and the hippocampus to the prefrontal cortex, the region of the brain at the very front of each cerebral hemisphere.  The functions of the prefrontal cortex are profoundly concerned with emotions, memory, learning and social behavior.

"Poor functioning of these limbic areas helps explain why violent offenders fail to learn from experience and are less able to regulate their emotions," Raine says.  "The subcortical findings are new and need to be replicated, but they are consistent with previous cognitive studies indicating that the more dominant left hemisphere may be less able to control the more emotional right hemisphere in violent offenders."

In 1994, Raine published the first evidence that murderers' brains show significantly lower rates of glucose uptake.  The initial research looked only at the prefrontal lobe, an area of the brain where deficits had already been linked with several mental illnesses, including schizophrenia and depression.

Raine's latest research demonstrates a more powerful link between brain damage and criminal violence, because it eliminates the possibility that mental disorders alone could have predisposed the criminal to violence.  "No mental disorder has been found to involve brain damage to all six of these brain areas showing metabolic abnormalities," Raine explains.

The lower glucose uptake observed in the six areas does not appear to reflect generalized brain dysfunction, he said.  Nor does it appear to be related to age, handedness, ethnicity, or recorded history of head injury.

If reduced metabolic activity in the six areas is in fact connected to homicidal tendencies in humans, then interventions to help reduce the damage would help reduce violence.  "Interventions must be made at an early age to have maximal impact," Raine cautions.

Known sources of brain damage to the six brain regions include vigorous shaking (which can lacerate white fibers that link the cortical circuits); fetal alcohol syndrome (which damages the corpus callosum); and eclampsia, an advanced stage of toxemia in pregnancy (which can damage the infant's hippocampus).  Other perinatal complications resulting in brain damage are less consistently related to specific regions of the brain. Forceps-related injuries, for example, can damage a number of brain areas.

Despite the strong link between brain damage and a propensity to violence in murderers, perinatal complications alone do not appear to predispose all individuals to crime, according to the American Journal of Psychiatry article.

Raine directed a team that looked at the medical histories of 4,269 Danish males born in the years 1959 through 1961. The team's obstetricians assessed birth complications at the time of delivery.  Interviews conducted with the infants' mothers at the end of the first year determined whether the boys had experienced maternal rejection.  Possibilities included mothers who simply did not want their pregnancies, who made unsuccessful attempts to terminate the pregnancy or who institutionalized their babies for more than four months in the first year of life.

USC researchers combed the Danish National Criminal Register to determine which of the subjects had a record of violence, theft or any other criminal behavior by the ages of 18 or 34.  The database, which includes all police contacts and court decisions involving Danish citizens, is one of the world's most comprehensive and accurate crime registers.

By the age of 18, boys whose mothers had experienced obstetrical complications were no more likely to have committed a violent crime than boys whose mothers had not.  But when these boys also experienced maternal rejection, their chances of committing a violent crime -- including robbery, murder and rape -- more than doubled (9% versus 4%).  Neither mental illness in the mothers nor recidivism among the offenders could account for the higher crime rates among this group.

Maternal rejection and obstetrical complications did not, however, seem to have the same effect among offenders who committed their first violent crime between the ages of 19 and 34.  Adults with these two biosocial risk factors were no more likely than normal adults to commit a violent crime, Raine said.

"Better prenatal care and counseling for at-risk mothers could lower the rate of violence perpetrated by juveniles and young adults, but it probably would not have the same effect on violent crimes perpetrated by older adults," Raine said.  "For late-onset adult offenders, we don't know as much about the underlying causes of violence.  The cause might be a head injury sustained in a traffic accident.  It might be alcoholism or other substance abuse.  Or it may turn out that these crimes are far more situational -- that is, caused by stress, a bad marriage or other sources of conflict."

Birth complications and maternal rejection appeared to predispose offenders to some kinds of criminal offenses but not others.  Offenders with both risk factors were nearly twice as likely as control subjects to rob, rape and commit murder.  While fewer than 5% of the control group had committed a violent crime by age 34, about 8% of the group with biosocial risk factors had done so.  The risk-factor subjects also were more likely than control subjects to commit an assault or domestic violence (5.5% versus 7.5%).

No such disparities were found, however, when the crimes involved threats of violence and weapons violations.  "The double hit of maternal rejection and obstetrical complications seems to predispose an individual to certain kinds of violent behavior, but not to lawlessness in general," Raine says.

The research team, which in 1996 discovered a link between these biosocial risk factors and the propensity to commit crime in a smaller group of subjects, also was able to determine which of the three types of maternal rejection interacted most strongly with perinatal complications.

In so doing, the researchers were able to rule out merely having negative feelings about the pregnancy as a risk factor for violent crime.  "Expectant mothers who don't want to bear children are often able to change their minds and bond with their child," Raine points out.  "It's the ones who take steps to rid themselves of their fetus or institutionalize their child who are the most problematic."

Institutionalizing a child for four months or more during the first year of life proved the most detrimental form of maternal rejection.  A mother's failed attempt to abort her fetus was the second most detrimental form.  "Either form of maternal rejection may predict child abuse and/or neglect," Raine notes.

"Proper bonding is important in the development of human compassion and empathy," Raine concludes.  "One ingredient of becoming a reckless, violent offender is being callous toward others.  The less an offender cares about you, the easier it is for him to hurt you to get what he wants."

Both studies were funded by a Research Science Development Award from the National Institutes of Health.

Raine is a professor of psychology in the USC College of Letters, Arts and Sciences and a research affiliate of USC's Center for the Study of Crime and Crime Control.  He is the author of "The Psychopathology of Crime:  Criminal Behavior as a Clinical Disorder" (1983) and has served as a consultant to the National Academy of Sciences on the biological bases of violence.