Adolescence is a critical period in a person’s cognitive development, during which their intellectual capacities and personality traits undergo profound changes. While such radical transformations often help prepare us for adulthood, they also open up new possibilities for the development of mental health disorders like depression and schizophrenia. In a groundbreaking new study, researchers from the University of Cambridge have observed the changes that occur in the adolescent brain on the eve of adulthood, revealing how they upgrade our cognition yet can also lead to the onset of certain mental illnesses.
Writing in the Proceedings of the National Academy of Sciences, the study authors explain that the thickness of the brain’s outer layer, known as the cortex, decreases as we age, as the brain “prunes” unnecessary or obsolete connections in a continual attempt to become more streamlined. Therefore, when performing MRI scans on 297 young people aged 14 to 24, the researchers were unsurprised to find that those at the younger end of the spectrum had thicker cortices than older participants.
In particular, the brain’s “hubs” – which exhibit the highest levels of connectivity and act as key communication points between various brain regions – were found to be very thick in 14-year-olds, while also containing low levels of myelin, an insulating material that coats neurons’ connecting branches in order to allow electrical impulses to be transmitted more efficiently.
Interestingly, findings revealed that over the course of one’s teenage years, these connectome hubs shrink in thickness at a much faster rate than the rest of the cortex, while also undergoing high levels of myelination. According to the researchers, this “synaptic remodelling and intracortical myelination of cortical hubs might be expected to minimize the conduction time” for electrical signals, thereby enhancing the overall processing speed and connectivity of the brain.
The brain's "hubs" undergo extensive shrinkage and myelination during one's teenage years. Whitaker, KJ, Vertes, PE et al. / PNAS
However, such radical changes to the structure of the brain also present opportunities for things to go wrong. Excessive “synaptic pruning”, for instance, has been associated with schizophrenia, and the study authors note that malfunctions during this teenage cerebral facelift could explain the high rates of mental health disorders in adolescence.
When looking at the genes that become expressed during this transformation, the researchers discovered that, unsurprisingly, many are strongly connected with the creation of proteins that play a role in myelination and synaptic construction. However, they also identified 349 genes that are associated with schizophrenia, all of which become expressed during this phase of adolescence.
Summarizing the dangers this poses, study co-author Edward Bullmore explained in a statement that “it's during these teenage years that those brain regions that have the strongest link to the schizophrenia risk genes are developing most rapidly.”
