People whose antisocial behavior starts in childhood and persists into adulthood have less grey matter in parts of their brain that play a role in motivation and emotional control, researchers have found.
Antisocial behavior — which psychologists sometimes diagnose as “conduct disorder” in childhood and adolescence — includes aggression, violence, stealing, bullying, lying, and repeated failure to fulfill school or work responsibilities.
The new brain imaging study is the first to compare adults with a lifetime history of this kind of behavior or those who only behaved in this way during adolescence with those who have rarely exhibited this behavior.
It adds to evidence that antisocial behavior that starts in childhood and continues into adulthood is associated with particular brain differences, whereas similar behavior occurring exclusively in adolescence is not.
The latter emerges in puberty and is more likely to be due to factors such as rebellion against parental authority, the researchers write in their paper, which features in The Lancet Psychiatry.
Their results suggest that people whose antisocial behavior starts in childhood, by contrast, have brain features that make it difficult for them to regulate their behavior.
The scientists used MRI scans to evaluate the brains of 672 45-year-old men and women whom researchers had closely studied since they were just 3 years of age.
The participants were part of the Dunedin Study, which has monitored the health and behavior of more than 1,000 people born in the early 1970s in Dunedin, New Zealand.
Based on self-reports and reports from their parents, caregivers, and teachers, the researchers categorized the participants as exhibiting life-course-persistent antisocial behavior or adolescent-only antisocial behavior, or as having no history of persistent antisocial behavior.
In comparison with the non-antisocial control group, people who had behaved antisocially since childhood had, on average, a slightly lower overall brain surface area and a thinner cortex, or outer brain layer.
Surface area and cortical thickness reflect the amount of gray matter in the cortex.
In addition, these participants had a significantly smaller surface area and thinner cortex in key regions associated with executive function, motivation, and emotion regulation.
In people who only exhibited antisocial behavior during adolescence, however, there were no widespread brain differences compared with either the life-course-persistent or control group.
Previous research suggests that while only about 9% of people behave antisocially from their childhood onward, they account for a disproportionately high number of criminal convictions and have worse physical and mental health.
It makes sense, therefore, to target behavioral and clinical interventions at this group from an early age.
The lead author of the new study, Dr. Christina Carlisi of University College London in the United Kingdom, says:
“Our findings support the idea that, for the small proportion of individuals with life-course-persistent antisocial behavior, there may be differences in their brain structure that make it difficult for them to develop social skills that prevent them from engaging in antisocial behavior. These people could benefit from more support throughout their lives.”
Carlisi emphasizes that most people who exhibit antisocial behavior do so only in adolescence, and they do not appear to have structural brain differences.
“It is also these individuals who are generally capable of reform and go on to become valuable members of society,” she says.
The researchers caution that their study does not prove that lifelong antisocial behavior occurs as a result of inherited brain differences.
It is possible that changes in the brain developed over time as a result of other risk factors that antisocial behavior strongly implicates, such as substance abuse, low IQ, and mental health problems.
Establishing which came first — the brain changes or the antisocial behavior — would require regular scans from childhood onward, the researchers write, alongside behavioral, genetic, and environmental measures.
In addition, they note that the findings relate to average brain differences across a large population of people, so it would be a mistake to apply them to individuals on the basis of MRI scans.
“Our findings support the need for different approaches for different offenders — however, we caution against brain imaging being used for screening, as the understanding of brain structure differences are not robust enough to be applied on an individual level.”
– Co-author Terrie Moffitt, Ph.D., Duke University, Durham, NC
Derek Hill, a professor of medical imaging at University College London, who was not involved in the study, agrees that the research does not offer a viable way to screen adolescents for future antisocial problems by scanning their brains.
Heredity accounts for about half of the variability in sociability between adults, he says, so early environmental influences, such as childhood abuse or poor nutrition, probably play equally important roles in future antisocial behavior.
Speaking to the Science Media Centre in London, he adds, “This research is a long way away from providing a way of identifying which antisocial teenagers are likely to be a long-term cost to society and which will, on their own, live normal adult lives.”