Chapter 1. Brain Development: Adolescence

Synopsis

Human Development Video Activity
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You must read each slide, and complete any questions on the slide, in sequence.
dendrite
Slender projections of the nerve cell body that receive electrical impulses from adjacent neurons.
neurons
A nerve cell that receives and communicates information throughout the body as part of the central nervous system.
prefrontal cortex
The part of the brain at the front of the frontal lobe just behind the forehead. It is responsible for executive functioning, such as decision-making, reasoning, planning, impulse control, and prioritizing tasks.
cerebral cortex
The folded outer layers of the brain covering the cerebrum that are critically involved in many complex functions, such as memory, attention, perceptual awareness, thought, language, and consciousness.
myelination
The growth of myelin on nerve cells. The myelin coating allows nerve impulses to travel faster.
synapse
The microscopic gap across which the axon of a neuron can transfer an electrical impulse to the dendrites of an adjacent neuron.
metabolism
All the physical and chemical processes that create or use energy for the body, such as breathing, digestion, regulating body temperature.
limbic system
A collection of structures below the cerebral cortex that are involved in the expression and regulation of emotions that are related to self-preservation, such as fear and anger, and to the pleasures of survival behaviors, such as eating and sex.
hormones
Chemical messengers that are produced in endocrine glands or other special cells, such as testes and ovaries, and travel via the bloodstream to target organs and tissues. Hormones are involved in the management and regulation of many bodily functions, such as digestion, breathing, sleeping, reproduction, growth, and mood.
adrenal glands
Located above the kidneys, the two adrenal glands produce hormones that help regulate the immune system, metabolism, blood pressure, and other essential functions.
gonads
Reproductive organs that produce gametes and sex hormones. The female gonads are the ovaries, and the male gonads are the testes.
puberty
The period of development when a person’s body transitions into adulthood. The sexual organs mature and the body readies for the possibility of reproduction.

Brain Development: Adolescence

Author

S. Stavros Valenti, Hofstra University

Eleven teens standing in a group – all smiling for the camera

Synopsis

In this activity, you will see animations and illustrations of the changes that occur in the brain during the teenage years. The relationship between these biological changes and adolescent behavior will also be explored.

REFERENCES

Kolb, B., & Whishaw, I. Q. (2001). An introduction to brain and behavior. New York: Worth Publishers.

Spear, L. (2000). The adolescent brain and age-related behavioral manifestations. Neuroscience and Biobehavioral Reviews, 24, 417-463.

The Teen Brain

Top photo - Eleven teenage girls from an athletic team all holding a trophy while looking excited and happy.  Lower photo – Teenage boy sitting on the ground holding a cigarette and a can of beer

In many respects, a person is at the peak of his or her physical capacities in the teenage years. Consider the number of outstanding teenage athletes in fields such as gymnastics, figure skating, or tennis. Many teenagers are happy and well adjusted. They look forward to the privileges and responsibilities of adulthood.

While the teenage years may be a positive experience for some, adolescents are also at greater risk for drug and alcohol abuse, reckless driving, depression, and criminal behavior.

How can we explain this rise in problem behaviors during adolescence? Some recent research suggests that brain development and hormonal changes may hold important clues for understanding why adolescence is so exciting, and yet at times, so difficult for teens and their families.

A Slow Growing Brain

An adult teaching a teen how to drive a car

The brain is still growing and changing during most of the teen years achieving its maximum size around the age of 18. At its peak, the brain weighs about 1.4 kilograms (about 3 pounds), which is about 4 times its weight at birth. Adolescence is a time of growth in the connections among neurons as well as a time of synaptic pruning and myelination. All of these developments act to further refine thoughts, actions, and behaviors and prepare the adolescent for adulthood.

The Prefrontal Cortex

The brain centers for sensation and perception are well developed during infancy, but other areas of the brain take much longer to mature. The frontal lobe within the cerebral cortex (in particular, the prefrontal cortex) shows significant changes from mid-childhood through the early 20s. This area of the cortex is responsible for inhibiting impulses, focusing attention, and planning — in short, all of the behaviors that we associate with intelligence, responsibility, and emotional maturity.

Question 1.1

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With the maturation of the prefrontal cortex, teenagers think with greater maturity, responsibility, and intelligence than ten or eleven year olds. These qualities would help the teenager make sounder decisions in a responsible job like that of babysitting young children.

Maturation of the Prefrontal Cortex: Synaptic Remolding and Myelination

Maturation of the prefrontal cortex is the result of two important changes at the microscopic level: myelination, which is the addition of myelin to the connecting fibers of neurons, and pruning, which is the remodeling of synaptic connections. Both of these changes yield a brain that processes information more quickly and efficiently.

Graph showing the change in synaptic density over time for both the prefrontal cortex and visual cortex.  The synaptic density in the prefrontal cortex steadily climbs until about 4 years old and then makes a gradual decline into adolescence.  There is a steep decline in synaptic density between adolescence and adulthood.  The synaptic density in the visual cortex climbs steeply from birth until the first year of life.  Then, the synaptic density makes a gradual decline from one year old into adulthood.
Synaptic connections in the prefrontal cortex are reduced and reorganized throughout adolescence and early adulthood. The visual cortex, in comparison, shows less maturation during this period.

Slowing of Metabolism

A teenage girl reading

Teen brains demonstrate a slower metabolism, which is another characteristic of maturity. A preschool child’s brain burns calories at higher-than-adult levels (hypermetabolism) in order to build new connecting fibers, synapses, and myelin. As the process of synaptic pruning customizes the brain making it more efficient, the brain metabolism declines from age 10 years until about 20 years of age.

Emotional Versus Intelligent Control of Behavior

A drawing showing the side view of the brain.  Labels show the occipital lobe at the back of the brain, the parietal lobe toward the top back of the brain, the temporal lobe just above the brain stem at the top of the spinal cord, and the frontal lobe just behind the forehead and the front of the skull.  The prefrontal cortex is a section of the frontal lobe directly behind the forehead.
There is a change in the balance of activity between the prefrontal cortex and the limbic system during adolescence. The limbic system is located deep within the brain on top of the brainstem and involves structures from the various lobes of the brain.

Some recent studies have suggested that there is a change in the balance of activity between the limbic system, which is involved in motivated behavior and automatic emotional reactions, and the prefrontal cortex, which is responsible for deliberate and thoughtful behavioral control. The specific nature of the interaction of these brain centers is unknown, but it is safe to say, “the adolescent brain is a brain in flux . . .” (Spear, 200, p. 438).

Raging Hormones?

A boy and a girl teenager arguing in a school hallway
Do hormones and brain changes cause teenagers to swing from one emotion to another? Or could it be that new opportunities and expectations cause these mood shifts?

Along with the brain changes that occur during adolescence, a rise in the level of hormones in the bloodstream also occurs. Hormones produced by the adrenal glands that are believed to increase the overall excitability of the brain begin to rise around 7 years of age and reach a plateau in late adolescence. Increasing levels of hormones produced by the gonads, which are responsible for the bodily changes of puberty, are also related to slight increases in moodiness, aggressive behavior, and aggressive thoughts in both males and females (Spear, 2000).

While there is good evidence for the idea that hormonal changes are related to behavioral changes, recent research has shown that this connection is a modest one at best. There is little support for the commonplace idea that risky teen behavior is caused by “raging hormones”.

Brain and Behavior: What is the Connection?

Teenage boy sitting on the ground holding a cigarette and a can of beer

What are we to make of these changes in the brain across adolescence? Researchers are careful to point out that “correlation is not causation.” Just because the brain is changing, it does not necessarily mean that these brain changes cause the unique behaviors of adolescence.

Researchers have offered some promising leads. The limbic system within the brain is involved in the way in which the brain experiences “reward” and “pleasure.” The observed shift in the balance of activity between the limbic system and the prefrontal cortex may be responsible for the well-documented decline in “pleasure” and “happiness” that is observed in early adolescence. Some researchers have described the adolescent as having a “mini reward-deficiency syndrome” that leads some to seek increased levels of stimulation through interaction with peers, risky behavior, and drug or alcohol use.

Brain and Behavior: The Role of Experience

An adult teaching a teen how to drive a car

Some researchers stress that the roots of adolescent risk-taking and impulsive behaviors stem from teenagers’ lack of relevant experiences and skills. Adults, after all, have many more years of experience with both the short and the long-term consequences of risky behavior.

Summary

Eleven teens standing in a group – all smiling for the camera

In this activity, you have seen that the teenage brain is truly “a brain in flux.” Remodeling of synaptic connections with the help of new experiences sculpts a new brain. The metabolism of the brain decreases throughout childhood and adolescence, and the balance of activity appears to change between the structures in the brain’s limbic system and the prefrontal areas of the cortex.

We also know that adolescence is a time of increased interactions with peers, new experiences outside the home, and new demands for mature behavior. These new interactions and experiences help adolescents develop new skills for coping with increased stresses, but the growth of these skills takes time.

A full understanding of the causes of teen behavior will depend on continued study and research of the brain and of the unique experiences of teenagers.

Assessment: Check Your Understanding

Eleven teenage girls from an athletic team all holding a trophy while looking excited and happy

Question 1.2

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Correct! The total number of neurons does not change much throughout adolescence. Much of the increase in the weight of the brain during adolescence is due to an overall increase in connecting dendrites of the neurons.
Sorry. The total number of neurons does not change much throughout adolescence. Much of the increase in the weight of the brain during adolescence is due to an overall increase in connecting dendrites of the neurons.

Assessment: Check Your Understanding

A teenage girl reading

Question 1.3

0vqmcsSJpdv5vE2NbNWT4TLpx5ZM0cN3stIK9p+TWmCketScWsiUCVl+zIBXvlW7yiiftX9NXa2UbPWfk4TALacKdGNrKAnxT2Rqhev/kFzzdxKu/2OUcSzdIGstcQvLUoyDFXwemkWybyVRmR8xr5jN3hwLgM1njyXp0OLLeQZyY+lgcaa+Xp9nCqkDWTAHDvrB8wCdbzRFLsPee504u8xpulEdTn8Q5wKKdD4mTFtBY+YJjC5LumYP2q6jxh+eQWrEZyjlR7pND7w9fUBKnnZBZ/8VIQtVZACJ8tqxE2F7yEw2OkfJieTyBUGpn/Vw7gkh8k/N6A3bUXXIHD4ni+27/ThipCKxQnak2VKYi+uoxgnz4Ng0YcqPqQTgt2UUiV4gccyR7p27yo24BJa2kjsgAok=
Correct! Myelination in the frontal lobe of the cortex is one of the changes that seems to promote efficient information processing and the inhibition of impulses in adolescence.
Sorry. Myelination in the frontal lobe of the cortex is one of the changes that seems to promote efficient information processing and the inhibition of impulses in adolescence.

Assessment: Check Your Understanding

A boy and a girl teenager arguing in a school hallway

Question 1.4

F/TkIv2gStR1rPK5py4xmYrkrFX8HEx6ya/BBJT+4LNHfDG4hSH7TPIW/nyKwduU1Q6CzmTQiLYTI8DopA/K+b3F4fR/MHtrwY8ZuYY9ZgV2nVJooh5mDkGAke8bILpv8fJQ33r8aH6yhSWg3CiqHF48tzGdAkOU+BpOz781pOLWHA5Pb/Ig7m0MrQb+I3TsFM87+Z0xlVy8NH7FuoefEo424m8WxKYVBKs+F1mlBSHD9+0Fr2LN+k2DVRV0yh3sYfpInJFkWJ9kgkSl7qXsisOMch9ga/NxiO8n10srFgOXypVwaLVgCg+D0otVtlSigDJlROdzUGOMFqSlc5PbLWRUofVeNWpICrscAj6uYwxm2xKueBZVCSqkQxCOQNj7QyP+Qv96lgXWAsVASI+NfJlFX5Lc4cBAV8PStD4wuuwB8PALM2Z2OwoKp8zEA3NJ8frEeGbwKCFn6NnEI/S8J5zGXFbuPtQ6XcPVu/TGx+bpkkw+
Correct! Researchers think that these changes are responsible for a shift away from emotional and impulsive behavior.
Sorry. Researchers think that these changes are responsible for a shift away from emotional and impulsive behavior.

Assessment: Check Your Understanding

Teenage boy sitting on the ground holding a cigarette and a can of beer

Question 1.5

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Correct! Recent research has shown that the relationship between adolescent hormonal change and behavior is modest at best.
Sorry. Recent research has shown that the relationship between adolescent hormonal change and behavior is modest at best.

Assessment: Check Your Understanding

An adult teaching a teen how to drive a car

Question 1.6

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Your answer should include: (a) shifts in activity from the limbic system to the prefrontal cortex, (b) an increase in myelination of the frontal cortex, (c) remodeling (pruning) of synaptic connection, and (d) an overall decrease in metabolism. Your answer may also mention hormonal changes.

Congratulations! You have completed this activity.Total Score: x out of x points (x%) You have received a provisional score for your essay answers, which have been submitted to your instructor.