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.
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.
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.