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It
now appears some of that baffling behavior of your teenage child
(or student) may be the result of neurobiology not raging hormones
For many
years it was thought that brain development was set at a fairly
early age. By the time teen years were reached the brain was
thought to be largely finished. However, scientists
doing cutting-edge research using magnetic resonance imaging,
or MRI, have mapped the brain from early childhood into adulthood
and found data contrary to these beliefs. It now appears the
brain continues to change into the early 20's with the frontal
lobes, responsible for reasoning and problem solving, developing
last.
The decade-long
magnetic resonance imaging (MRI) study of normal brain development,
from ages 4 to 21, by researchers at NIH's National Institute
of Mental Health (NIMH) and University of California Los Angeles
(UCLA) shows that such "higher-order" brain centers, such as
the prefrontal cortex, don't fully develop until young adulthood
as grey matter wanes in a back-to-front wave as the brain matures
and neural connections are pruned. (see figure 1).
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FOR
TIME LAPSE PHOTOGRAPHY SEE BELOW
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Figure
1.
Time-Lapse
Imaging Tracks Brain Maturation from ages 5 to 20
Constructed
from MRI scans of healthy children and teens, the time-lapse
"movie", from which the above images were extracted, compresses
15 years of brain development (ages 5–20) into just a
few seconds.
Red
indicates more gray matter, blue less gray matter. Gray
matter wanes in a back-to-front wave as the brain matures
and neural connections are pruned.
Source:
Paul Thompson, Ph.D. UCLA Laboratory of Neuroimaging
http://www.nimh.nih.gov/press/prbrainmaturing.cfm?styleN=one
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In
calm situations, teenagers can rationalize almost as well as
adults. But stress can hijack what Ron Dahl, a pediatrician
and child psychiatric researcher at the University of Pittsburgh
Medical Center calls "hot cognition" and decision-making.
The frontal lobes help put the brakes on a desire for thrills
and taking risk -- a building block of adolescence; but, they're
also one of the last areas of the brain to develop fully.
Although
scientists don't know yet what accounts for the observed changes,
they may parallel a pruning process that occurs early in life
that appears to follow the principle of "use-it-or-lose-it:"
neural connections, or synapses, that get exercised are retained,
while those that don't are lost.
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Brain
Tissue Changes in Development (15 year timespan)
Time-lapse
Imaging Tracks Brain Developing from ages 5 to 20 NIMH/UCLA
Project Visualizes Maturing Brain
Source:
Paul Thompson, Ph.D. UCLA Laboratory of Neuroimaging
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"The
most surprising thing has been how much the teen brain
is changing. By age six, the brain is already 95 percent
of its adult size. But the gray matter, or thinking part
of the brain, continues to thicken throughout childhood
as the brain cells get extra connections, much like a
tree growing extra branches, twigs and roots...
...In
the frontal part of the brain, the part of the brain involved
in judgment, organization, planning, strategizing -- those
very skills that teens get better and better at -- this
process of thickening of the gray matter peaks at about
age 11 in girls and age 12 in boys, roughly about the
same time as puberty. After that peak, the gray matter
thins as the excess connections are eliminated or pruned...
...But
the pruning-down phase is perhaps even more interesting,
because our leading hypothesis for that is the "use it
or lose it" principle. Those cells and connections that
are used will survive and flourish. Those cells and connections
that are not used will wither and die. So if a teen is
doing music or sports or academics, those are the cells
and connections that will be hard-wired. If they're lying
on the couch or playing video games or MTV, those are
the cells and connections that are going [to] survive...
...Right
around the time of puberty and on into the adult years
is a particularly critical time for the brain sculpting
to take place...
...
It;s sort of unfair to expect teens to have adult levels
of organizational skills or decision-making before their
brains are finished being built...
...The
frontal lobe is often called the CEO, or the executive
of the brain. It's involved in things like planning and
strategizing and organizing, initiating attention and
stopping and starting and shifting attention. It's a part
of the brain that most separates man from beast, if you
will...
...I
think that [in the teen years, this] part of the brain
that is helping organization, planning and strategizing
is not done being built yet ... [It's] not that the teens
are stupid or incapable of [things]. It's sort of unfair
to expect them to have adult levels of organizational
skills or decision making before their brain is finished
being built. ...
...doing
drugs or alcohol that evening, it may not just be affecting
their brains for that night or even for that weekend,
but for the next 80 years of their life..."
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Excerpts
from an interview with Jay Giedd:
Jay Giedd, M.D. is a practicing Child and Adolescent
Psychiatrist and Chief of Brain Imaging at the Child Psychiatry
Branch of the National Institute of Mental Health
For full interview see:
Inside the Teenage Brain
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IMPLICATIONS
OF STUDIES
One
goal is to learn what teachers can do to take advantage of the
time when their students' brains change the most. If some parts
of the brain develop sooner than others, for example, perhaps
school subjects should be taught in a different order.
Teenagers
are four times as likely as older drivers to be involved in
a crash and three times as likely to die in one, according to
the Insurance Institute for Highway Safety. "Right now our first
subjects are reaching driving age," Giedd said. "What better
application could there be than saving their lives?"
Knowing
what their brains are going through might also motivate teenagers
to change their own priorities. "What you do with your brain
during that time," Giedd says, "could have a lot of good and
bad implications for the rest of your life."
Eventually,
brain studies might help resolve conflicts at home. Teenagers
are capable of learning a lot, but the parts of their brains
related to emotions and decision-making are still in the works.
As their brains undergo rewiring, teenagers are particularly
vulnerable to risky behavior, such as drinking and driving too
fast.
Brain immaturity
can explain why the teen crash rate is so high.
RECENT UPDATES
A recent
study by Lebel and Beaulieu (see below) reinforce the above
findings that the human brain doesn't stop developing at adolescence,
but continues well into our 20s. The
study is the first long-range investigation, using a type of
imaging that looks at brain wiring and shows that in the white
matter there are still structural changes happening during young
adulthood. The white matter connects different regions to facilitate
cognitive abilities. The study suggests that connections are
strengthening even as we age in young adulthood.
C. Lebel,
C. Beaulieu. Longitudinal
Development of Human Brain Wiring Continues from Childhood into
Adulthood. Journal of Neuroscience, 2011.
| Abstract:
Healthy human brain development is a complex process that
continues during childhood and adolescence, as demonstrated
by many cross-sectional and several longitudinal studies.
However, whether these changes end in adolescence is not
clear. We examined longitudinal white matter maturation
using diffusion tensor tractography in 103 healthy subjects
aged 5–32 years; each volunteer was scanned at least twice,
with 221 total scans. Fractional anisotropy (FA) and mean
diffusivity (MD), parameters indicative of factors including
myelination and axon density, were assessed in 10 major
white matter tracts. All tracts showed significant nonlinear
development trajectories for FA and MD. Significant within-subject
changes occurred in the vast majority of children and early
adolescents, and these changes were mostly complete by late
adolescence for projection and commissural tracts. However,
association tracts demonstrated postadolescent within-subject
maturation of both FA and MD. Diffusion parameter changes
were due primarily to decreasing perpendicular diffusivity,
although increasing parallel diffusivity contributed to
the prolonged increases of FA in association tracts. Volume
increased significantly with age for most tracts, and longitudinal
measures also demonstrated postadolescent volume increases
in several association tracts. As volume increases were
not directly associated with either elevated FA or reduced
MD between scans, the observed diffusion parameter changes
likely reflect microstructural maturation of brain white
matter tracts rather than just gross anatomy. |
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