The structural changes of developing teenage brains have been mapped by scientists, who say this new evidence may explain why the first symptoms of mental illness often appear before adulthood.
In the study, published in the Proceedings of the National Academy of Sciences, the brains of almost 300 individuals aged 14-24 years old were examined by researchers from the University of Cambridge and University College London. Using magnetic resonance imaging (MRI), they found that the cortex – the outer regions of the brain – becomes thinner during adolescence. However, at the same time, levels of myelin – the material which forms an insulating sheath around nerve fibres in the brain – increase within the cortex. Myelin facilitates effective communication between nerve fibres, which partly explains the development of the brain during this time period.
Although myelin has here been identified within the cortex, the brain’s ‘grey matter’, which is primarily associated with processing and cognition, it was previously thought to be found mainly in ‘white matter’, brain tissue that coordinates communication between different regions of the brain. Researchers found that myelin not only exists within the cortex but increases during the teenage years, particularly in the ‘association cortical areas’, which act as connection hubs between different brain regions.
One of the study’s authors, Dr Kirstie Whitaker from the Department of Psychiatry at the University of Cambridge, summarised the findings: “During our teenage years, our brains continue to develop. When we’re still children, these changes may be more dramatic, but in adolescence we see that the changes refine the detail. The hubs that connect different regions are becoming set in place as the most important connections strengthen. We believe this is where we are seeing myelin increasing in adolescence.”
The link to mental health issues was revealed when the researchers compared their MRI results with the Allen Brain Atlas, a database which maps gene expression patterns in the brain. They found that the brain regions in which genes linked to schizophrenia were most strongly expressed, or ‘switched on’, were the same regions that exhibited the greatest MRI changes during adolescence.
This process was explained by Professor Ed Bullmore, Head of Psychiatry at Cambridge: “Adolescence can be a difficult transitional period and it’s when we typically see the first signs of mental health disorders such as schizophrenia and depression. This study gives us a clue why this is the case: it’s during these teenage years that those brain regions that have the strongest link to the schizophrenia risk genes are developing most rapidly.
Delving further into the implications these findings have on our understanding of the development of mental illness, Professor Bullmore said: “As these regions are important hubs that control how regions of our brain communicate with each other, it shouldn’t be too surprising that when something goes wrong there, it will affect how smoothly our brains work.
“If one imagines these major hubs of the brain network to be like international airports in the airline network, then we can see that disrupting the development of brain hubs could have as big an impact on communication of information across the brain network as disruption of a major airport, like Heathrow, will have on flow of passenger traffic across the airline network.”
Dr Raliza Stoyanova, part of the Neuroscience and Mental Health team at the Wellcome Trust, which funded the study, commented on its findings: “A number of mental health conditions first manifest during adolescence. Although we know that the adolescent brain undergoes dramatic structural changes, the precise nature of those changes and how they may be linked to disease is not understood.
“This study sheds much needed light on brain development in this crucial time period, and will hopefully spark further research in this area, and tell us more about the origins of serious mental health conditions such as schizophrenia.”
Whitaker, KJ, Vertes, PE et al. Adolescence is associated with genomically patterned consolidation of the hubs of the human brain connectome. PNAS; 25 July 2016; DOI: 10.1073/pnas.1601745113