2017 Children’s Mental Health Report
Brain Development 101
We humans don’t have a lot else going for us other than our wiles and wit. Our competitive edge is our ingenuity, brains over brawn. This edge happens to take the longest to develop, as the connectivity to and from the frontal lobes is the most complex and the last to fully mature. This “executive function” thus develops slowly; we certainly are not born with it!
The human brain is an incredible thing, and it takes its time growing up. While the brain is never “finished” — every experience we have makes real, physical changes in our brains all our lives — the period of major structural and connective development continues from before birth into early adulthood. Adolescence is an important period of this development.
- Neural circuits, or systems, are responsible for most of what we can do and learn as humans — like speech, movement, emotional regulation, complex reasoning and more. Different systems develop throughout a child’s first 25 years. Early childhood is important because so many systems are developing then. Adolescence also has a number of key systems developing.
- In addition to developing new connections, the brain also “prunes” connections into a more efficient arrangement. This happens over the first few years of life, and again in adolescence.
- When each brain system is developing, it is “plastic” and susceptible to disruption. Thus, the environment and activities of teens have significant impacts on brain structure and connectivity throughout the lifespan.¹ ²
- Areas responsible for cognitive control in the pre-frontal cortex are the last to become mature and efficiently connected. The process of growth, pruning and consolidation continues throughout adolescence into what is sometimes called emerging adulthood, the period from roughly 11 to 25 years of age.
- Although some brain illnesses have clear genetic causes, many mental health disorders appear to be the result, in part, of stressful experiences that cause brain changes and connections that are not helpful for the individual in our society.
 Giedd, J. N., Blumenthal, J., Jeffries, N. O., Castellanos, F. X., Liu, H., Zijdenbos, A., & … Rapoport, J. L. (1999). Brain development during childhood and adolescence: a longitudinal MRI study. Nature Neuroscience, 2(10), 861.
 Paus, T., Keshavan, M., Giedd, J.N. (2008). Why do many psychiatric disorders emerge during adolescence? Nature Reviews Neuroscience, 9(12), 947–957. doi:10.1038/nrn2513.