Conduct problems – including persistent rule-breaking, aggression, irritability and difficulty following school rules – are associated with small but widespread differences in brain structure, according to a major international study of more than 14,000 children and adolescents, led by the University of Bath.
Importantly, these brain changes were found not to be limited to young people with a formal diagnosis of conduct disorder – a mental health condition in children and adolescents characterised by persistent patterns of antisocial behaviour. Instead, they were present across the full range of severity, including in youngsters with mild behavioural difficulties.
The study’s authors say this research marks an important step forward in understanding the biological and developmental roots of conduct problems, with the potential to inform more effective, tailored interventions for young people worldwide.
The research, published this week in the Journal of the American Academy of Child & Adolescent Psychiatry, was conducted by the international ENIGMA Antisocial Behavior Working Group. It was led by Dr Marlene Staginnus and co-authored by Professor Graeme Fairchild, both from the Department of Psychology at the University of Bath.
According to the team’s findings, the more serious a young person’s conduct problems, the more pronounced the differences in their brain structure. The researchers found this to be true for the thickness of the cortex (the outer layer of the brain), the surface area of the cortex and the size of key subcortical regions – areas found deeper in the brain.
The cortex is responsible for many key functions, including thinking and reasoning, decision-making, communication, and understanding emotions and social behaviour. The authors found that the greater the conduct problems, the thinner and smaller the cortex.
The subcortical regions highlighted in the study are involved in emotional learning and experience, and memory. These areas were smaller in young people with conduct problems.
Beyond high-income countries
The study, which analysed MRI scans from people aged 5 to 21 across 18 different samples in 12 countries, is the largest study of its kind to date. It is also among the first to include substantial data from low- and middle-income countries, including India and Brazil, making the findings relevant across the globe.
Dr Staginnus said: “These results suggest that the physical and biological characteristics of the brain linked to conduct problems are not restricted to severe or clinically diagnosed cases but are present across a continuum. This supports a more nuanced view of behaviour and mental health.
“Our findings have important implications. Conduct problems are known to be associated with a range of negative outcomes, including poorer mental health, educational challenges and increased likelihood of becoming involved with the criminal justice system.
“By improving our understanding of the biology of conduct problems, the research highlights the importance of recognising and supporting conduct problems across the spectrum of severity and may help inform more effective prevention and early intervention strategies.”
Professor Fairchild added: “Our results challenge earlier theories that focused on a narrow set of brain regions linked to emotion processing. Instead, the study suggests that conduct problems are associated with more widespread differences across much of the brain.”
Less stigmatisation, more nuanced diagnoses
The authors insist their findings should be interpreted with caution. The observed effects were small, so it is likely that not all youth with conduct problems show these brain differences.
Also, brain structure alone does not determine behaviour, with environmental factors – such as parenting, social context and exposure to traumatic experiences – likely to play a central role.
The researchers stress that this work should not be used to label or stigmatise children and adolescents. Rather, it is intended to support a more informed understanding of how behavioural difficulties develop. The results also provide further evidence that behavioural difficulties should be conceptualised as a mental health condition.
The findings may have implications for how mental health conditions are classified. By strengthening evidence that behavioural difficulties exist along a spectrum rather than as a simple yes-or-no diagnosis, the study supports moves towards a more nuanced approach in both research and clinical practice.
As a next step, the researchers hope to follow a cohort of young people over time to understand how brain structure and conduct problems influence one another during development, particularly across childhood and adolescence.
This study was funded by the ESRC through a PhD studentship to Marlene Staginnus. Dr Sophie Townend and Professor Esther Walton from the Department of Psychology at Bath also contributed, along with Professor Stéphane De Brito and Dr Yidian Gao from the University of Birmingham and ENIGMA collaborators from across the world.