1. Why Do They Do That? Brain Development During Adolescence
Daniel Krowchuk, M.D.
Departments of Pediatrics and Dermatology
Wake Forest University School of Medicine

2. Objectives
Describe changes in brain structure and function that occur during adolescence
Discuss the implications of these changes with respect to adolescent behavior and health promotion strategies

3. The leading cause of death for teenagers in the U. S. is A. AIDS B
The leading cause of death for teenagers in the U.S. is A. AIDS B. cancer C. homicide D. suicide E. unintentional injury

4. Deaths, Percent of Total Mortality, and Death Rates by Cause, 15-19 year olds, U.S., 2004
Number
Percent
Rate/100,000
All Causes
13,706
100.0
66.1
Unintentional injury
6,825
49.8
32.9
Homicide
1.932
14.1
9.3
Suicide
1,700
12.4
8.2
Malignancy
731
5.3
3.5
-Data reviewed 4/10/09 – this table is most recent analysis that contains yo data (more recent reports have data for yo)
Among those years of age, of accidents 76% were due to MVA
-Homicide is the leading cause of death for AA males (63.2/ 100,000)
-US has the highest youth homicide and suicide rates among the 36 wealthiest nations in the world
Heron M. National Vital Statistics Reports 2007;56(5)

5. What percent of high school seniors report having been drunk. A. 25% B
What percent of high school seniors report having been drunk? A. 25% B. 40% C. 55% D. 70% E. 85%

6. Lifetime Prevalence of Use (%) of Various Substances by High School Seniors
1980
1985
1990
1995
2000
2003
2006
2007
2008
Any illicit
drug
65.4
60.6
47.9
48.4
54.0
51.1
48.2
46.8
47.4
Marijuana
60.3
54.2
40.7
41.7
48.8
46.1
42.3
41.8
42.6
LSD
9.3
7.5
8.7
11.7
11.1
5.9
3.3
3.4
4.0
Ecstasy -
11.0
8.3
6.5
6.2
Cocaine
15.7
17.3
9.4
6.0
8.6
7.7
8.5
7.8
7.2
Been drunk
63.2
62.3
58.1
56.4
55.1
54.7
Cigarettes
71.0
68.8
64.4
64.2
62.5
53.7
47.1
44.7
Study begun with class of 1975
Low for marijuana (32.6) and any illicit drug (40.7) in 1992
Ecstasy: first asked in 1996 (6.1)
Been drunk: first asked in 1991 (65.4)
(1/09)

7. Adolescence Physical Development (Puberty) Early Adolescence Middle
Late
Adolescence
Social and Emotional Maturation
Adolescents aged years represent >40 million persons or 14% of the US population
Physical development: gain 20% of adult height and 50% of adult weight; physical changes occur transforming the individual from a child to an adult
10 – 13 years
14 – 16 years
17 – 21 years
Cognitive Development

8. Social and Emotional Maturation
Emotional separation from parents
Develop a sense of personal identity and self-image
Identify with a peer group
Explore romantic relationships
With respect to developing a positive self-image, parents should notice an adolescent’s positive qualities and offer praise for these
Physical illness can have a significant impact on self-esteem – can make adolescent feel flawed or different from peers. May also interfere with ability to separate from parents.
Hazen E, et al. Pediatr Rev 2008;29:

9. Cognitive Development
Increased ability to think abstractly
Greater impulse control
Improved ability to assess risk vs. reward
Improved use of working memory (the information in memory available for working on a problem)
Young drivers seem more likely than older ones to underestimate the probability of the specific risks of certain traffic situations and to overestimate their own ability to manage such risks. Thus, adolescents engage in risky behaviors because of problems in judging risk appropriately and in accurately perceiving their own vulnerability.
Working memory: functioning in the world requires one to consider antecedents and consequences and place the steps of a plan in the proper order
Cognitive alterations are associated with
changes in brain structure and function
Hazen E, et al. Pediatr Rev 2008;29:
Casey BJ. Ann NY Acad Sci 2008;1124:

10. Neuroanatomy Review Gray matter (cerebral cortex): White matter:
Contains nerve cell bodies
Processes and routes information
Increases in pre-adolescence then
decreases
White matter:
Composed of nerve cell extensions (axons) that convey information (e.g., from gray matter)
Color results from myelin coating of axons (acts as insulation that allows nerve impulses to travel more rapidly and efficiently)

11. Changes in Brain Anatomy
Each new experience results in new connections between neurons
By the end of adolescence, the brain contains
billion neurons
Forming 100 trillion connections with one other
100 billion – 1 trillion support cells
Increased intelligence, reasoning, problem-solving
New experiences like new vocabulary word, dance step, etc.
The more one is involved in an activity, the more dendrites grow and the more synaptic connections develop
Weinberger DR, et al. The Adolescent Brain: A Work in Progress.
National Campaign to Prevent Teen Pregnancy; 2005.

12. Changes in Brain Anatomy
Pruning
Information that is regularly used is retained – that which is unimportant or used infrequently is lost as the result of pruning (a loss of cells or connections)
Adolescents may lose 15% of synaptic connections/year (compared with 1-2% for adults)
Results in greater efficiency
Myelination
Fatty covering of axons that acts as insulation
Permits more rapid (100-fold) and efficient communication
Increases into the third decade
Brain operates on a “use it or lose it” philosophy
Pruning: eg, important dates of battles in the Civil War may be lost but cause of Civil War and important ramifications are retained
Myelination increases speed at which signals can travel up to 100-fold compared with unmyelinated axons
Weinberger DR, et al. The Adolescent Brain: A Work in Progress.
National Campaign to Prevent Teen Pregnancy; 2005.

13. Brain Development and Risk Taking
Lateral prefrontal cortex
(Cognitive control)
Impulse control
Setting priorities
Formulating plans
Decision-making
Envisioning
consequences of actions
Risk taking is the product of an interaction between two brain networks the socioemotional network (located in the limbic and prelimbic areas [amygdala, ventral striatum, orbitofrontal cortex, medial prefrontal cortex, and superior temporal gyrus]) and the cognitive-control network (lateral prefrontal and parietal cortices). The former becomes more assertive during puberty and the latter gains strength over time.
Limbic system develops before the prefrontal cortex is mature (ie, accelerator but no brakes) – also, myelination is not complete until the 30s so the speed and efficiency of communication with the prefrontal cortex is not optimal
Limbic system
(Socioemotional)
-Impulsiveness
-Sensation-seeking

14. Risky Business – The Role of Peers
Among adolescents, many high risk behaviors take place in groups
Substance use
Reckless driving
Crimes
Are adolescents more susceptible to the influences of risk-prone peers?
When compared with adults, adolescents who commit crimes ranging from vandalism to rape or homicide tend to do so in the company of one or more indviduals

15. Risky Business – The Role of Peers
Risky decision-making asessed in:
106 adolescents (13-16 yrs)
105 youths (18-22 yrs)
95 adults (>24 yrs)
Decision-making assessed using video game
Alone
In group with 2 other subjects who could offer advice
Watch car move across screen until
yellow traffic light appears
Stop car before red light and wall appear
More points the further the car moved
without crashing into wall
Gardner M, Steinberg L. Dev Psychol 2005;41:

16. Risk Preference Scale 5 hypothetical scenarios
Having sex without a condom
Riding in a car driven by someone who has been drinking
Trying a new drug one knows nothing about
Breaking into store to steal something one wants
Driving over 90 mph on highway at night
Ranked 1 (risks are much greater than benefits) to 4 (benefits are much greater than risks)
Gardner M, Steinberg L. Dev Psychol 2005;41:

17. Risky Business – The Role of Peers
Younger individuals:
Allowed car to move further after yellow light
Chose riskier course of action on questionnaire
Were more likely to be affected by peer influences
Gardner M, Steinberg L. Dev Psychol 2005;41:

18. Risk-Reward and Brain Activity
Nucleus accumbens
Component of the limbic system
Involved in processing rewards
Cortex receives stimulus indicating reward
Nucleus accumbens and other areas are activated leading to repetition of the gratifying behavior
Develops earlier than the prefrontal cortex
When the cortex has received and processed a sensory stimulus indicating a reward, it sends a signal announcing this reward to a particular part of the midbrain–the ventral tegmental area (VTA)–whose activity then increases. The VTA then releases dopamine not only into the nucleus accumbens, but also into the septum, the amygdala, and the prefrontal cortex. The nucleus accumbens then activates the individual’s motor functions, while the prefrontal cortex focuses his or her attention.
These regions are connected by what is called the pleasure or reward bundle. In neuroanatomical terms, this bundle is part of the medial forebrain bundle (MFB), whose activation leads to the repetition of the gratifying action to strengthen the associated pathways in the brain.
Galvan A, et al. J Neurosci 2006;26:

19. Risk-Reward and Brain Activity
Functional MRI performed during tasks weighing risk and reward
Adolescents activate the nucleus accumbens more than adults
Nucleus accumbens activity correlates with anticipation of a positive consequence of a risky behavior (which, in turn, correlates with the likelihood of engaging in risky behaviors) – more pronounced in adolescents Ad
Individuals who expect a negative consequence of a behavior show less accumbens activity and are less likely to participate in the behavior
Individual variations in neurobiology influence risky behavior – for some individuals, the perceived immediate benefits (of sex, substance use) may outweigh negative long-term consequences. Increased accumbens activity likely related to impulsivity.
Galvan A, et al. J Neurosci 2006;26:
Galvan A, et al. Dev Sci 2007;10:F8-F14

20. Substance Use and the Brain
Limbic system - prefrontal cortex connections grow into early adulthood.
Certain of these neurons use dopamine to relay messages
These neurons increase capacity for more mature thought (choices based on memory not impulse)
Cocaine and amphetamines target these dopaminergic neurons.
Connections are necessary for communication between the 2 areas and to facilitate (ultimately) the delay of gratification necessary to achieve desired outcomes (ie, override inappropriate choices in favor of goal-related ones). Myelination also continues into the 30s.
Important if one is to follow an idea in pursuit of a goal (rather than acting on instinct).
Alcohol affects structures that use GABA as a neurotransmitter (cortex, cerebellum, hippocampus, amygdala, nucleus accumbens) – alcohol inhibits normal neurogenesis, the process by which new neurons are created (higher levels of intake have greater effects)
Weinberger DR, et al. The Adolescent Brain: A Work in Progress. National Campaign to Prevent Teen Pregnancy; 2005.

21. “Hot” and “Cold” Cognition
“Hot” cognition
Decision made in an emotionally-charged situation
Adolescent surrounded by peers in a stimulating environment may make an emotionally-based decision
“Cold” cognition
Decision made in a calmer, quieter environment
Adolescent may make a more intellectual, consequence-based decision
Social skills training (i.e., role-playing) may be beneficial in moderating “hot” cognitions.

22. Recognizing Emotions
Adolescents often misinterpret body language and words that are spoken
A parent stares at their adolescent waiting for a response to a question – the adolescent interprets the stare as the parent being angry.
An adolescent looks across the lunchroom at an acquaintance; the acquaintance happens to turn her head in the other direction – the adolescent may interpret that she has been shunned.
Adapted from Feinstein S. Secrets of the Teenage Brain.
Thousand Oaks, Ca: Corwin Press; 2004

23. Recognizing Emotions
Complex network of brain regions involved in recognizing
Basic emotions (fear)
Social emotions (guilt, embarrassment, shame)
Network includes:
Amygdala
Medial prefrontal cortex
Anterior insula
Superior temporal sulcus
The network above all are components of the limbic/prelimbic system discussed earlier
The mPFC is different than the lateral PFC (involved in more restraint, executive functions)
Blakemore S-J. Nat Rev Neurosci 2008;9:

24. Do Adolescent and Adults Differ?
Adults and adolescents presented with the photograph of a woman with an expression of fear on her face
All adults correctly interpreted the emotion as fear
Half of adolescents thought that the woman expressed shock or surprise
Blakemore S-J. Nat Rev Neurosci 2008;9:

25. Processing Emotions
19 adolescents ( years) and 10 adults (22 – 32 years) underwent functional MRI scanning1 while thinking about scenarios involving:
Basic emotions (e.g., disgust, fear)
Social emotions (e.g., embarrassment, guilt, shame)
Requires awareness on your part of others’ opinions of your action
Study performed to examine neural processing of social emotions in adolescents and adults
Embarrassment scenarios: “Your father dances in the supermarket” or “Your were picking your nose and someone saw you” or “You were eating with a friend and dropped food on your shirt”
Burnett S, et al. J Cogn Neurosci 2009;21:
Burnett S, Blakemore S-J. Ann NY Acad Sci 2008;1167:51-56

26. Processing Emotions
Adolescents activate more of the medial prefrontal cortex
Experiencing social emotions is different in adolescents
Perhaps adolescents are still “working out” social situations
Less efficient and automatic
Adults activate more of the anterior temporal horn than adolescents
Still working out social situations based on accumulating experience or developing social skills
With age, processing may become less effortful, more automatic, and more reliant on stored social knowledge
Inefficient thinking is characteristic of adolescents. As a result they may not be able to shut out extraneous input and may be more distractable (for young drivers, a reason to limit the number of passengers in the car, avoid the radio and cell phones)
Burnett S, et al. J Cogn Neurosci 2009;21:
Burnett S, Blakemore S-J. Ann NY Acad Sci 2008;1167:51-56

27. How Not to Embarrass a Teen1
Don’t correct or reprimand her in front of others.
Don’t fix his clothes, straighten his tie, or tuck in his shirt in public.
Don’t call her by a pet nickname in front of her friends.
Don’t kiss, hug, or show affection on school grounds.
Don’t run into the middle of class to bring something he’s forgotten.
In early to mid adolescence, teenagers become aware of and concerned about other’s opinions of them; they also believe that others spend time observing them
1Elias Z, Goldman T. How Not to Embarrass Your Kids: 250 Don’ts for Parents of Teens.
New York, NY: Warner Books; 2009

28. Conclusions
Adolescents see and react to the world differently than children or adults
Late maturation of areas of the brain responsible for complex thought processes helps explain
Delayed psychosocial maturation
Adolescent behavior (including involvement in risky endeavors)
Adolescents need supportive parents, adults, and institutions that provide guidance and help them learn appropriate skills and adult behaviors
One study found that young drivers seem more likely than older ones to overestimate the probability of specific risks of certain traffic situations and to overestimate their own ability to manage such risks. Involvement in risky behaviors (experimentation with alcohol, involvement in sexual activity) occurs because teens have difficulties judging risk appropriately and in accurately perceiving their own vulnerability.

29. Implications
Health promotion
Public policy

30. Tobacco Use
9.4% of high school students use cigarettes frequently (>20 of 30 days/month)1
Half of the 3000 adolescents who begin smoking each day will become daily smokers2
90% of adult smokers began smoking as adolescents2
1Centers for Disease Control and Prevention. Youth Risk Behavior Surveillance.
2Ziedonis D, et al. Adolesc Med Clin 2006;17:

31. Preventing Tobacco Use
Standard approach:
Advise adolescent of adverse effects of tobacco use
Developmentally appropriate approach:
Parental supervision
Policy making:
Prohibiting sale of tobacco to minors
Prohibit tobacco advertising
Prohibit tobacco use on school grounds (students, staff, parents)

32. Preventing Tobacco Use
3834 youths years interviewed 3 times over a 4-year period
Odds of progressing from experimentation to established smoking reduced by 40% in towns with strong restaurant smoking regulations
9.6% risk in towns with weak regulations vs. 7.9% for towns with strong regulations
Rationale:
Reduce youths’ exposure to tobacco in public places (lowers perception of smoking prevalence)
Change perceived social acceptability of smoking
Smoking can be influence by community-level factors not just personal-level ones
3834 in baseline sample (interviewed 1/2/01-6/18/02); 2791 (72.8%) of these reinterviewed 1/30/03-7/31/04; 2045/2791 reinterviewed 2/16/05-3/26/06.
Weak regulations: smoking not restricted or nonsmoking section; medium: enclosed separately ventilated space; strong: no smoking
Other variables assoc with progression to established smoking: older age group (18-21) at baseline (OR 2.02), previous experimentation with cigarettes, adult smoker in house (OR 1.54), presence of a close friend who smokes (OR 1.91)
Both of the rationale statements would influence transition from experimentation to regular use. Parental smoking and education level are significant predictors of smoking experimentation (but not transition to regular smoking).
Siegal M, et al. Arch Pediatr Adolesc Med 2008;162:

33. Brain Development and Policy
Roper v. Simmons (2005, US Supreme Court)
17-year-old convicted of murder and sentenced to death
American Psychological Association (APA) and AMA filed briefs arguing that adolescents’ still developing brains made them different than adults. Death penalty was outlawed if offender <18 years of age when crime committed.
Hodgson v. Minnesota (1990, US Supreme Court)
Case challenged Minnesota law requiring parental consent for abortion. The APA argued that by age 14 or 15 years, adolescent decision making was essentially equivalent to that of an adult.
Decision in Roper v. Simmons hinged on culpability which involves the offender’s state of mind at the time of the offense, including factors that would
mitigate, or lessen, the degree of responsibility.
The apparent inconsistency of these 2 decisions could be argued from the standpoint of hot and cold cognitions (ie, cold cognition in the context of an abortion related decision (employs more mature judgment) as opposed to the hot cognition context of a murder.
The year after Roper v. Simmons, Kansas used neuroscience research to expand the state’s child abuse statute to include any consensual touching between minors under the age of 16.
Johnson SB, et al. J Adolesc Health 2009;45: