The adolescent brain is best described as a work in progress. Our brains are about 90-95% of their maximum size by the time we are 6 years old, but they are definitely not finished changing! Massive changes continue to occur over the next 15-20 years, as connections within the brain are strengthened and refined. Adolescent brain development can be divided into three processes: proliferation, pruning and myelination.

1. Everything you need
to know about the
Teen Brain

2. Significant brain growth and development occurs
during adolescence and continues into the twenties
adolescence, twenties.
Some studies show that this growth and
development extends to the age of 30!
(Sowell et al., 1999; Sowell et al., 2001)

3. Adolescent brain development can be divided
into three processes:
• Proliferation (rapid growth of brain matter and the
formation of new connections within the brain)
• Pruning (cutting away of unused or unimportant
ti )
connections)
• Myelination (insulating of brain pathways to
make them faster and more stable) )
(Sowell et al., 1999; Sowell et al., 2001)

4. Proliferation: Total brain volume
By age 6, the brain is
about 95% of its
maximum size.
* It reaches its maximum
size at 11.5 years in
g
girls*, and at 14.5 years
, y
in boys*. (Giedd et al., 1999)
*
Boys brains are larger
(on average) than girls
brains.
b i
Lenroot & Giedd (2006)

5. Remember…
Maximum brain size
does not mean
maximum brain
maturity!
The brain continues to
mature for at least
another 10 years.

6. Remember…
And although boys
brains are anatomically
bigger than girls brains,
size is not directly
related to intelligence.

7. The tissue of the brain can be divided into two
types of matter, grey and white. These
tissues grow and mature at diff
ti d t t different rates.
t t
Grey matter looks grey
to the naked eye. It is White matter looks white
composed of neuron cell
f to the naked eye, and is
eye
bodies, dendrites, and glial made up of axons.
cells.
cells

8. Grey matter is where all the
thinking happens This is your
happens.
brain’s processing centre.
White matter, containing those
long axons, are like a super
highway. They transport
information to different parts
of your brain
brain.
Photo credit (CC 2.0): facemepls, MSVG

9. Proliferation: Grey Matter
Grey matter develops
G tt d l
quickly during childhood,
but slows during adolescence.
Grey matter volume peaks
at age 11 in girls and at
g g
age 13 in boys.
Then, the volume of grey
matter begins to decline.
Lenroot & Giedd (2006)

10. Pruning: Grey Matter Maturation
 The maturation of grey matter is best described
as a constant “push and pull”. New
pathways grow, while others are pruned back.
 Pruning is greatly influenced by experience, so
it really is a case of “use it or lose it”!
!
 This makes the adolescent brain extremely
versatile, and able to make changes
depending on the demands of the environment
environment.

11. Pruning: Grey Matter Maturation
The brain matures in a back-to-front pattern. The frontal
pattern
& temporal lobes are the last to mature.
Remember: the frontal lobe is the home of planning
planning,
organization, judgment, impulse control and reasoning!
mporal
ontal
Parietal
Fro
Tem
Lenroot & Giedd (2006)

12. Proliferation and Myelination: White matter
White matter makes up myelin,
which insulates axons and
speeds up the communication
between neurons.
It develops continuously from
* birth onwards, with a slight
increase during puberty
puberty.
* The increase occurs just after the
peak in grey matter volume (around
age 11 in girls* and around age 13
in boys*).
Lenroot & Giedd (2006)

13. Say that again?!
Teens show a consistent pattern
of brain development.
f
White matter increases in a Grey matter follows an upside-
roughly linear pattern. The down U shape. The pattern differs
pattern is similar in different according to brain region
region.
brain regions.
White Grey

14. The Teen Brain is in a
Constant State of Development
And some areas of the brain
mature f t th others. The
t faster than th Th
areas of your brain associated
with reward, motivation, and
reward motivation
impulsivity matures early. Photo credit (CC 2.0): Daniel Flower

15. The Teen Brain is in a
Constant State of Development
Your prefrontal cortex,
cortex
which thinks about things
logically,
logically weighs the pros
and cons, and restrains
y
you matures later. This
means teens can be more
prone to riskier and
impulsive behaviors, and
less likely to consider
consequences than an
adult would be. Photo credit (CC 2.0): Alaskan Dude

16. Risk and Reward
It’s not that teens are stupid,
or have no control over their
own brain. Studies have shown
that teens know when they are
engaging in risky behavior (like
unprotected sex, drinking, or
drugs). However they are more
likely to think that the benefits of
those behaviors outweigh any
potential harm.
Reyna & Farley (2007) Photo credit (CC 2.0): winnifredxoxo

17. Risk and Reward
It’s important to take a step
back and realize that though not
every risky choice will result in
harm – some will. It’s not
enough to know there’s risk, you
need to also understand the
consequences. It could impact Playing Russian Roulette
the rest of your life in a really with one bullet is certainly
much safer than playing it
negative way. with five. But should we
really be playing it at all?
Reyna & Farley (2007) Photo credit (CC 2.0): Andres Bastidas

18. So how does the brain
mature after adolescence?
There is evidence that these
changes continue WELL
after the teenage years.
f
In a study of young adults, the frontal lobes
showed large changes up to the age of 30!
This suggests that frontal lobe maturation is
important for adult cognition.
(Sowell et al., 1999; Sowell et al., 2001)

19. What does all this mean?
It means huge advances
have been made in studies
of brain development.
p

20. BUT…
BUT
it is difficult to figure out
exactly how these
structural brain changes
relate to functional changes
in cognition and behavior.

21. Hopefully, the answers to
these questions will come
within the next few years.

22. References
Giedd, J.N., Blumenthal, J Jeffries N O Castellanos F.X., Liu, H., Zijdenbos, A.,
Giedd J N Blumenthal J., Jeffries, N.O., Castellanos, F X Liu H Zijdenbos A
Paus, T., Evans, A.C., Rapoport, J.L. 1999. Brain development during childhood and
adolescence: A longitudinal MRI study. Nature Neuroscience. 2: 861-863.
Lenroot, R.K., Giedd, J.N. 2006. Brain development in children and adolescents:
Insights from anatomical magnetic resonance imaging. Neuroscience and Biobehavioral
Reviews. 30: 718-729.
Sowell, E.R., Thompson, P.M., Holmes, C.J., Jernigan, T.L., Toga, A.W. 1999. In vivo
evidence for post-adolescent brain maturation in frontal and striatal regions. Nature
Neuroscience. 859-861.
Neuroscience 2: 859-861
Sowell, E.R., Thompson, P.M., Toga, A.W. 2001. Mapping continued brain growth and
gray matter density reduction in dorsal frontal cortex: Inverse relationships during
postadolescent brain maturation. The Journal of Neuroscience. 21: 8819-8829.
Reyna, V. F.
Reyna V F and Farley F 2007 Is the teen brain too rational? Scientific American
Farley, F. 2007.
Mind. 17: 58-65

23. Sun Life Financial Chair
In Adolescent Mental Health
For more information visit
WWW.TEENMENTALHEALTH.ORG