The brain structure of young people with conduct disorder differs significantly from that of their typically developing peers. This is the conclusion of an international study that analysed more than two thousand MRI scans, recently published in The Lancet Psychiatry. Dr Moji Aghajani, one of the principal investigators, explains why this discovery is crucial both clinically and societally.
Is there a biological basis for antisocial behaviour? This is the question Aghajani and his colleagues worldwide seek to answer within the ENIGMA Antisocial Behaviour working group. 'It is a controversial question,' he says. 'Because it suggests that there may be something biologically wrong with people who exhibit criminal behaviour, aggression, or are imprisoned. This implies a degree of inevitability - can they still be rehabilitated? Are they responsible for their actions?' However, Aghajani argues, to reduce or even prevent antisocial behaviour, it is essential to understand how the brains of these young people develop.
'There isn't a single brain region, gene, or personality trait that solely accounts for antisocial behavior'
Antisocial behaviour
Aghajani and his colleagues analysed brain scans of 1,185 young people with conduct disorder alongside those of 1,253 typically developing peers. Conduct disorder is one of the most common psychiatric disorders among young people, with far-reaching social, emotional, and economic consequences. Those affected are often locked in a cycle of severely antisocial behaviour, characterised by aggression, rule-breaking, and a disregard for others' boundaries. About 30 percent of these youngsters also exhibit callous, psychopathic traits, showing no remorse or empathy for the harm they cause others. Conduct disorder is sometimes considered a precursor to antisocial personality disorder or psychopathy in adulthood.
A sum of small effects
The data came from fifteen different datasets worldwide, including brain scans from young people in psychiatric facilities and prisons across the Netherlands, Asia, North America, and Europe. 'This heterogeneous sample renders our findings more generalizable to the actual patient population,' Aghajani explains, whilst enhancing the reproducibility of our results, a key factor given the ongoing replication crisis in behavioural sciences.
These large samples were subjected to a centrally coordinated mega-analysis by the ENIGMA researchers, benefiting from the robustness of consortium collaboration. 'This makes the statistics more solid, but does not necessarily increase the effect sizes - quite the opposite. The more heterogenous and rigorous our approach, the smaller the effects appear. Psychiatric disorders probably arise due to accumulation of various small effects, rather than any single brain region, gene, or personality trait.'
A controversial research field
This research builds on earlier work, including that of Dutch criminologist Wouter Buikhuisen, who in the 1970s sought to investigate the biological basis of antisocial behaviour. His work sparked considerable backlash from colleagues and the media, leading to threats and bomb scares, ultimately resulting in his dismissal from Leiden University. However, in 2009, he was reinstated, as the notion that biological factors might play a role in antisocial behaviour gained broader acceptance.
Structural brain differences
In their analysis, the researchers found various structural and morphological differences in the brains of young people with conduct disorder. 'We observed that the cortex, the brain's outer layer, as well as subcortical areas, which lie deeper in the brain, were smaller and less developed in these youngsters,' Aghajani explains. 'The interplay between the cortex and subcortical regions enables us to perform complex tasks and regulate emotions. This network also facilitates empathy and helps us relate to others. If someone we're talking to starts crying, for instance, we naturally wonder if we might have done something wrong.'
The most significant differences were observed in a subgroup exhibiting psychopathic traits, such as a lack of empathy. These structural abnormalities may explain why young people with severe antisocial behaviour struggle with skills like emotion regulation and empathy. Many experts consider conduct disorder a neurodevelopmental disorder, meaning a condition where normal brain development is disrupted.
'We observe that multiple brain regions are less developed in young people with conduct disorder'
Impaired brain development
The ENIGMA Antisocial Behaviour consortium's research suggests that young people with conduct disorder might experience impaired brain development. 'This affects all brain-directed behaviours: attention, emotion regulation, behavioural regulation, and planning. These young people may struggle to gauge the consequences of their actions for themselves and others, partly because they lack the empathy to do so. Empathy may be the most crucial deterrent against antisocial behaviour - if you feel empathy for someone, it's very hard to harm them or steal their belongings,' says Aghajani.
Brain development is likely hindered by a combination of adverse biological and environmental factors. 'Consider a mother who experiences chronic stress or substance abuse during pregnancy. This may offset normative fetal brain development, rendering her child biologically susceptible to mental health disorders. Growing up in poverty, in high-crime areas, or experiencing emotional or physical abuse can further add to this disrupted brain development. Together, these biological and environmental risks can increase a child's likelihood of developing antisocial behaviour or even conduct disorder.'
'Empathy may be the most crucial deterrent against antisocial behaviour'
Predicting antisocial behaviour
'In the long run, we hope to create predictive models based on risk profiles, ultimately gaining a comprehensive understanding of conduct disorder and antisocial behaviour,' Aghajani explains. This knowledge could help identify which young people are likely to overcome/outgrow the disorder and who might require closer monitoring. In the long term, this research also aims to contribute to a targeted treatment protocol for conduct disorder. 'At present, there is no evidence-based treatment protocol for conduct disorder. For some young people with conduct disorder, therapy currently focuses on underlying trauma in the hope that this may reduce antisocial behaviour - and sometimes this is successful. However, we ultimately hope to contribute to a treatment protocol that directly addresses the disorder itself, benefiting the majority of these young people.'
