Problems with the brain’s ability to prune itself of unnecessary connections may be linked to adolescent mental health disorders, a new study suggests.
The findings could help explain why people are often affected by more than one mental health disorder, and may in future help identify those at greatest risk, researchers say.
According to the World Health Organisation (WHO), one in seven adolescents (aged 10-19) worldwide experiences mental health disorders.
It also says depression is one of the leading causes of illness and disability among adolescents, with half of all mental health disorders in adulthood starting by age 14 but most undetected and untreated.
Another mental health disorder that may emerge during adolescence is anxiety which, together with depression, appears as internalising symptoms, including low mood and worrying.
Other conditions such as attention deficit hyperactivity disorder (ADHD) manifest as externalising symptoms, such as impulsive behaviour, experts say.
Professor Barbara Sahakian from the department of psychiatry at the University of Cambridge said: “Young people often experience multiple mental health disorders, beginning in adolescence and continuing – and often transforming – into adult life.
“This suggests that there’s a common brain mechanism that could explain the onset of these mental health disorders during this critical time of brain development.”
In the new study, led by researchers in the UK, China and Germany, the scientists identified a characteristic pattern of brain activity among these adolescents, which they have termed the ‘neuropsychopathological factor’ (NP).
The discovery of this factor could help identify young people at greatest risk of compounding mental health problems.
Professor Jianfeng Feng from Fudan University in Shanghai, China, and the University of Warwick, UK, said: “We know that many mental health disorders begin in adolescence and that individuals who develop one disorder are at increased risk of developing other disorders too.
“By examining brain activity and looking for this NP factor, we might be able to detect those at greatest risk sooner, offering us more opportunity to intervene and reduce this risk.”
The researchers examined data from 1,750 14-year-olds, from the Imagen cohort, a European research project looking at how biological, psychological and environmental factors during adolescence may influence brain development and mental health.
In particular, they examined brain scans taken while the teenagers took part in cognitive tasks to see how different regions of the brain communicate with each other.
According to the findings, the teens who experienced mental health problems showed similar patterns of brain activity.
This was regardless of whether their disorder was one of internalising or externalising symptoms, or whether they experienced multiple conditions.
The study found these patterns – the NP factor – were largely apparent in the area at the front of the brain responsible for executive function which, among other functions, controls flexible thinking, self-control and emotional behaviour.
The researchers confirmed their findings by replicating them in 1,799 people from the ABCD Study in the USA, a long-term study of brain development and child health, and by studying patients who had received psychiatric diagnoses.
Genetic data from the Imagen group indicated the NP was strongest in those who carried a particular variant of the gene IGSF11 that has been previously associated with multiple mental health disorders.
This gene plays an important role in synaptic pruning, a process whereby unnecessary brain connections – synapses – are discarded.
Because the frontal lobes are the last brain areas to complete development in adolescents and young adults, the researchers suggest problems with pruning may particularly affect these regions.
Dr Tianye Jia from the Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, Shanghai, China and King’s College London, said: “As we grow up, our brains make more and more connections. This is a normal part of our development.
“But too many connections risk making the brain inefficient. Synaptic pruning helps ensure that brain activity doesn’t get drowned out in ‘white noise’.
“Our research suggests that when this important pruning process is disrupted, it affects how brain regions talk to each other.
“As this impact is seen most in the frontal lobes, this then has implications for mental health.”
The study, funded by the National Natural Science Foundation of China, European Union, National Institute for Health and Care Research (UK) and National Institutes of Health (US), is published in Nature Medicine.
