Presentation on theme: "Why Do They Do That? Brain Development During Adolescence"— Presentation transcript:
1Why Do They Do That? Brain Development During Adolescence Daniel Krowchuk, M.D.Departments of Pediatrics and DermatologyWake Forest University School of Medicine
2ObjectivesDescribe changes in brain structure and function that occur during adolescenceDiscuss the implications of these changes with respect to adolescent behavior and health promotion strategies
3The 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
4Deaths, Percent of Total Mortality, and Death Rates by Cause, 15-19 year olds, U.S., 2004 NumberPercentRate/100,000All Causes13,706100.066.1Unintentional injury6,82549.832.9Homicide1.93214.19.3Suicide1,70012.48.2Malignancy7315.33.5-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 worldHeron M. National Vital Statistics Reports 2007;56(5)
5What 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%
6Lifetime Prevalence of Use (%) of Various Substances by High School Seniors 198019851990199520002003200620072008Any illicitdrug65.460.647.948.454.051.148.246.847.4Marijuana60.354.240.741.748.846.142.341.842.6LSD188.8.131.521.7184.108.40.206.44.0Ecstasy-11.08.36.56.2Cocaine15.717.39.46.08.220.127.116.11.2Been drunk63.262.358.156.455.154.7Cigarettes71.068.864.464.262.553.747.144.7Study begun with class of 1975Low for marijuana (32.6) and any illicit drug (40.7) in 1992Ecstasy: first asked in 1996 (6.1)Been drunk: first asked in 1991 (65.4)(1/09)
7Adolescence Physical Development (Puberty) Early Adolescence Middle LateAdolescenceSocial and Emotional MaturationAdolescents aged years represent >40 million persons or 14% of the US populationPhysical development: gain 20% of adult height and 50% of adult weight; physical changes occur transforming the individual from a child to an adult10 – 13 years14 – 16 years17 – 21 yearsCognitive Development
8Social and Emotional Maturation Emotional separation from parentsDevelop a sense of personal identity and self-imageIdentify with a peer groupExplore romantic relationshipsWith respect to developing a positive self-image, parents should notice an adolescent’s positive qualities and offer praise for thesePhysical 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:
9Cognitive Development Increased ability to think abstractlyGreater impulse controlImproved ability to assess risk vs. rewardImproved 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 orderCognitive alterations are associated withchanges in brain structure and functionHazen E, et al. Pediatr Rev 2008;29:Casey BJ. Ann NY Acad Sci 2008;1124:
10Neuroanatomy Review Gray matter (cerebral cortex): White matter: Contains nerve cell bodiesProcesses and routes informationIncreases in pre-adolescence thendecreasesWhite 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)
11Changes in Brain Anatomy Each new experience results in new connections between neuronsBy the end of adolescence, the brain containsbillion neuronsForming 100 trillion connections with one other100 billion – 1 trillion support cellsIncreased intelligence, reasoning, problem-solvingNew 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 developWeinberger DR, et al. The Adolescent Brain: A Work in Progress.National Campaign to Prevent Teen Pregnancy; 2005.
12Changes in Brain Anatomy PruningInformation 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 efficiencyMyelinationFatty covering of axons that acts as insulationPermits more rapid (100-fold) and efficient communicationIncreases into the third decadeBrain operates on a “use it or lose it” philosophyPruning: eg, important dates of battles in the Civil War may be lost but cause of Civil War and important ramifications are retainedMyelination increases speed at which signals can travel up to 100-fold compared with unmyelinated axonsWeinberger DR, et al. The Adolescent Brain: A Work in Progress.National Campaign to Prevent Teen Pregnancy; 2005.
13Brain Development and Risk Taking Lateral prefrontal cortex(Cognitive control)Impulse controlSetting prioritiesFormulating plansDecision-makingEnvisioningconsequences of actionsRisk 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 optimalLimbic system(Socioemotional)-Impulsiveness-Sensation-seeking
14Risky Business – The Role of Peers Among adolescents, many high risk behaviors take place in groupsSubstance useReckless drivingCrimesAre 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
15Risky 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 gameAloneIn group with 2 other subjects who could offer adviceWatch car move across screen untilyellow traffic light appearsStop car before red light and wall appearMore points the further the car movedwithout crashing into wallGardner M, Steinberg L. Dev Psychol 2005;41:
16Risk Preference Scale 5 hypothetical scenarios Having sex without a condomRiding in a car driven by someone who has been drinkingTrying a new drug one knows nothing aboutBreaking into store to steal something one wantsDriving over 90 mph on highway at nightRanked 1 (risks are much greater than benefits) to 4 (benefits are much greater than risks)Gardner M, Steinberg L. Dev Psychol 2005;41:
17Risky Business – The Role of Peers Younger individuals:Allowed car to move further after yellow lightChose riskier course of action on questionnaireWere more likely to be affected by peer influencesGardner M, Steinberg L. Dev Psychol 2005;41:
18Risk-Reward and Brain Activity Nucleus accumbensComponent of the limbic systemInvolved in processing rewardsCortex receives stimulus indicating rewardNucleus accumbens and other areas are activated leading to repetition of the gratifying behaviorDevelops earlier than the prefrontal cortexWhen 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:
19Risk-Reward and Brain Activity Functional MRI performed during tasks weighing risk and rewardAdolescents activate the nucleus accumbens more than adultsNucleus 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 adolescentsAdIndividuals who expect a negative consequence of a behavior show less accumbens activity and are less likely to participate in the behaviorIndividual 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
20Substance Use and the Brain Limbic system - prefrontal cortex connections grow into early adulthood.Certain of these neurons use dopamine to relay messagesThese 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” cognitionDecision made in an emotionally-charged situationAdolescent surrounded by peers in a stimulating environment may make an emotionally-based decision“Cold” cognitionDecision made in a calmer, quieter environmentAdolescent may make a more intellectual, consequence-based decisionSocial skills training (i.e., role-playing) may be beneficial in moderating “hot” cognitions.
22Recognizing EmotionsAdolescents often misinterpret body language and words that are spokenA 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
23Recognizing EmotionsComplex network of brain regions involved in recognizingBasic emotions (fear)Social emotions (guilt, embarrassment, shame)Network includes:AmygdalaMedial prefrontal cortexAnterior insulaSuperior temporal sulcusThe network above all are components of the limbic/prelimbic system discussed earlierThe mPFC is different than the lateral PFC (involved in more restraint, executive functions)Blakemore S-J. Nat Rev Neurosci 2008;9:
24Do Adolescent and Adults Differ? Adults and adolescents presented with the photograph of a woman with an expression of fear on her faceAll adults correctly interpreted the emotion as fearHalf of adolescents thought that the woman expressed shock or surpriseBlakemore S-J. Nat Rev Neurosci 2008;9:
25Processing Emotions19 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 actionStudy performed to examine neural processing of social emotions in adolescents and adultsEmbarrassment 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
26Processing EmotionsAdolescents activate more of the medial prefrontal cortexExperiencing social emotions is different in adolescentsPerhaps adolescents are still “working out” social situationsLess efficient and automaticAdults activate more of the anterior temporal horn than adolescentsStill working out social situations based on accumulating experience or developing social skillsWith age, processing may become less effortful, more automatic, and more reliant on stored social knowledgeInefficient 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
27How 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 them1Elias Z, Goldman T. How Not to Embarrass Your Kids: 250 Don’ts for Parents of Teens.New York, NY: Warner Books; 2009
28ConclusionsAdolescents see and react to the world differently than children or adultsLate maturation of areas of the brain responsible for complex thought processes helps explainDelayed psychosocial maturationAdolescent behavior (including involvement in risky endeavors)Adolescents need supportive parents, adults, and institutions that provide guidance and help them learn appropriate skills and adult behaviorsOne 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.
30Tobacco Use9.4% of high school students use cigarettes frequently (>20 of 30 days/month)1Half of the 3000 adolescents who begin smoking each day will become daily smokers290% of adult smokers began smoking as adolescents21Centers for Disease Control and Prevention. Youth Risk Behavior Surveillance.2Ziedonis D, et al. Adolesc Med Clin 2006;17:
31Preventing Tobacco Use Standard approach:Advise adolescent of adverse effects of tobacco useDevelopmentally appropriate approach:Parental supervisionPolicy making:Prohibiting sale of tobacco to minorsProhibit tobacco advertisingProhibit tobacco use on school grounds (students, staff, parents)
32Preventing Tobacco Use 3834 youths years interviewed 3 times over a 4-year periodOdds of progressing from experimentation to established smoking reduced by 40% in towns with strong restaurant smoking regulations9.6% risk in towns with weak regulations vs. 7.9% for towns with strong regulationsRationale:Reduce youths’ exposure to tobacco in public places (lowers perception of smoking prevalence)Change perceived social acceptability of smokingSmoking can be influence by community-level factors not just personal-level ones3834 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 smokingOther 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:
33Brain Development and Policy Roper v. Simmons (2005, US Supreme Court)17-year-old convicted of murder and sentenced to deathAmerican 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 wouldmitigate, 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: