Overview
Though it has long been known that teenagers are prone to impulsive
behavior, to emotional rather than logical thinking, and to not fully
considering the long-term consequences of their actions, only recently
has neuroscience and MRI technology provided an understanding of why.
The teenage brain, it turns out, is a brain still developing. To
understand the risks associated with psychoactive substances in
adolescents, it helps to understand that teenagers are not just
less-experienced adults; they are undergoing an important yet
challenging developmental stage in which that are prone to errors of
judgment, and sensitive to neurological assault by psychoactive
substances. More than any other age group adolescents are at risk for
substance addiction, and more than any other age group they risk
permanent intellectual and emotional damage due to the effects of drugs.
Normal Adolescent Brain Development
The human brain is sculpted by experience. At birth, the brain
contains many more neural connections than it could possible use, but
these connections are unspecialized and undeveloped. As time passes
some connections are strengthened (such as the nerves that process the
sight of a mother’s face or sound of a siblings’ voice) and others are
pruned away.
The process of refinement and pruning continues throughout
childhood, adolescence, and even into early adulthood. The most marked
development in adolescence is in the brain’s frontal lobe and outer
mantle. The pre-frontal cortex, located in the frontal lobe, executes
such skills as setting priorities, formulating strategies, allocating
attention and controlling impulses; the outer mantle is involved with
processing abstract information and understanding rules, laws and codes
of social interaction.
The behaviors that accompany these changes are transparent.
Teenagers are notorious for their obsession with social interaction,
for making up social rules and breaking them. As teenagers grow into
young adults they often exhibit a fascination with abstract thinking on
topics like history, culture and media, which demonstrates their
growing ability to understand the larger world. While the teenage brain
is in some ways ill equipped to make decisions and choices without the
help of trusted adults, it is perfectly designed for the types of
intellectual and social challenges teenagers most need to master.
Still, development of fully mature complex thinking takes a long
time. MRI studies show that the development of the prefrontal cortex
and outer mantle of the brain continues into the early 20s, and may not
be completed until the mid 20s. As the wiring for logical thought is
used more and more over time the connections become more robust, and
when this process nears completion, parts of nerves become coated in a
fatty layer called a “myelin sheath.” Like insulation on a wire, this
fatty layer allows the nerve connections to process faster, making
rational, reasoned decision-making quicker and more automatic.
Effects of Drugs on the Developing Brain
There are many ways that psychoactive substances can alter or damage
the development of the adolescent brain. Firstly, psychoactive
substances often target and alter function of neurotransmitters, the
chemical messengers that allow nerves to communicate at their
junctions. Interference with neurotransmitters can directly damage
fragile developing neural connections. Secondly, use of these
substances alters perception and may interfere with the developing
perceptual skills. And finally, the habits and choices associated with
the use of drugs and alcohol slowly become ingrained in the wiring of
the brain. Repeated action becomes habit and the habits of thought,
perception, and reasoning developed in childhood and adolescence can
stay with a person throughout his or her lifetime.
Neurotransmitter Function
Alterations in neurotransmitter function are partially responsible
for both the high addiction potential and the devastating effects of
methamphetamines and cocaine. The neurotransmitter dopamine links the
nerves in the outer mantle and prefrontal cortex of the brain and is
associated with the feelings of motivation and reward. When adolescents
use the problem solving circuitry of the brain, they experience
feelings of both reward and motivation. Over time teens become more and
more motivated to think through problems, and more likely to develop
better solutions as they refine the neural circuitry associated with
these skills.
Methamphetamines and Cocaine are known to cause a flood of dopamine
into the brain. This is one reason for the extreme addiction potential
of these drugs: their use is associated with a tremendous sense of
reward. It has been found, though, that cocaine addicts have a blunted
perception for certain types of reward, and it is hypothesized that
cocaine, and by extension methamphetamines, over time override the
brain’s ability to sense rewards accurately in day-to-day interactions.
The effects of these drugs can be devastating not only to intellectual
development, but to the very ability of the user to feel satisfaction
from life.
Alterations in Perception
Perceptual changes caused by drugs can also have long-term
complications for adolescent development, since adolescent perceptive
abilities are not fully mature. For example, MRI studies show that
adults tend to use the frontal lobes, or logical problem solving, to
determine facial expressions while adolescents use the amygdala, an
area which normally processes emotions such as fear and worry. It holds
true in many studies that where adults use problem solving areas of the
brain to perceive the world adolescents use the more primitive areas
of the brain more associated with emotions, and self-preservation; it
also holds true that adult perception is generally more accurate.
Marijuana, like all drugs, changes perception. And like most drugs,
it engenders perception that is fearful, emotional, defensive, and
often inaccurate. Though the short term addiction potential of
marijuana may be less than other drugs, the long-term impact of chronic
marijuana use can be profound. Determining the feelings and motives of
other people is necessary to function as an adult in society. If
marijuana use is chronic or constant enough to hinder perceptual
maturation, an adolescent user may encounter misunderstood failures in
school, work, and relationships, which in turn re-enforce the desire to
retreat to drugs.
Habit and the Hard Wiring of the Brain
As self help gurus are quick to point out, if you do something for
long enough it becomes automatic. Nowhere does this wisdom more hold
true than in adolescence. Though teens may change clothes, ideas,
friends and hobbies with maddening frequency, they are developing ideas
about themselves, their world and their place in it that will follow
them for the rest of their lives. Adults may spend years trying to
create or break even the simplest habit, yet most adults find that
their most profound ideas about themselves and the world were developed
in high school or college. This is because, by age 25 or so the brain
is fully developed and building new neural connections is a much slower
process.
Conclusion
Early detection and treatment is essential to heading off the
development of substance addiction in adolescents. Given their brain
development, teenagers cannot be expected to understand the full range
of consequences in their choices regarding drugs and alcohol. The
disease must be prevented, and where it cannot be prevented it must be
cured while there is still time for a full recovery.
Information Taken from The Adolescent Brain: A Work in Progress ,
Daniel R. Weinberger, MD, Brita Elvevag, PhD, and Jay N. Giedd, MD, for
The National Campaign to Prevent Teen Pregnancy, 2005.
