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Adolescent Brain Development

Adolescent Brain Development Sara Salek, M.D. Medical Director for Children’s Services Division of Behavioral Health Services Arizona Department of Health Services

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Adolescent Brain Development

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  1. Adolescent Brain Development Sara Salek, M.D. Medical Director for Children’s Services Division of Behavioral Health Services Arizona Department of Health Services

  2. “We now know through science that the first three years of life is the most critical time period. It is the time period when the brain develops at a greater rate than any time during the course of a person’s life….but by age 10 your brain is cooked and there’s nothing much you can do.” –Rob Reiner, National Governor’s Association Speech Feb ‘97

  3. Goals of Presentation • Discuss basic brain anatomy and function • Provide overview on brain development in humans • Describe our current understanding of adolescent phase of brain development • Review concerns about alcohol use in the adolescent phase of brain development

  4. Introduction: The Human Brain • The most complex three pound mass in the known universe • At fours weeks gestation, neurons are forming at 250,000 per minute •  90% of its adult size by age 6 • The average adult brain contains around 100 billion neurons

  5. Prefrontal Cortex • “CEO” of the brain • Memory • Voluntary Motor Control • Attention • Reasoning • Planning • Decision Making • Impulse Control • Abstract Thinking

  6. Gray vs. White Brain Matter • Gray Matter • Neurons’ cell bodies and dendrites • “Thinking” portion of brain • White Matter • Insulation for neurons = myelination • Enhances efficiency

  7. Brain Development • 3-4 weeks gestation • Key events in CNS development • Fold of ectodermal tissue into neural tube • 4-12 weeks gestation • Neural tube becomes different parts of nervous system • Forebrain and spinal cord develop • Source: Lenroot RK. Giedd JN. Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. [Review] [94 refs] Neuroscience & Biobehavioral Reviews. 30(6):718-29, 2006.

  8. Brain Development • 12-20 weeks gestation Neurons multiply and migrate • 15 weeks gestation Surface of brain begins to fold into sulci and gyri Source: Lenroot RK. Giedd JN. Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. [Review] [94 refs] Neuroscience & Biobehavioral Reviews. 30(6):718-29, 2006

  9. Brain Development • 20 weeks gestation Proliferation and organization of synapses • 24 weeks gestation to 4 weeks after birth Rapid cell death Source: Lenroot RK. Giedd JN. Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. [Review] [94 refs] Neuroscience & Biobehavioral Reviews. 30(6):718-29, 2006

  10. Critical Periods • Window of time in which brain must receive certain type of stimuli to develop optimally • Examples in humans • Vision • Hearing

  11. Introduction: Adolescence • Interplay of changes • Emotions • Hormones • Physical Body • Judgment

  12. Adolescence: Definition Transition from childhood to adulthood • No fixed age range • Individual acquires skills necessary to survive on own

  13. Adolescence: Behavior Behavior characterizing adolescence Increased risk-taking and novelty seeking

  14. Adolescence: Puberty • Puberty = sexual maturation process that occurs during adolescent period • Puberty ≠ Adolescence • Girls begin puberty 1-2 years before boys

  15. Adolescence: Puberty • Hormonal Change: • Hypothalamic-Pituitary-Gonadal Axis • Gonadotropin-releasing hormone from hypothalamus • FSH and LH from pituitary gland • Estrogen and testosterone from ovary • Testosterone from testis

  16. Adolescence: Societal View • Societal Limitations • Consume Alcohol • Marriage • Vote • Join military

  17. Adolescence: Brain Development • Unique Process • Neuronal circuitry changing • Discoveries made possible by advanced brain imaging technology

  18. Imaging in Children/Adolescents • Studies previously limited: CT scans and x-rays exposed children to ionizing radiation • Magnetic Resonance Imaging (MRI) • Non-ionizing radiation • Provides detailed images of brain

  19. MRI Studies of Brain Development • 1980s • First MRI studies of brain development • 1990s • General findings: white matter increases and gray matter decreases Source: Lenroot RK. Giedd JN. Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. [Review] [94 refs] Neuroscience & Biobehavioral Reviews. 30(6):718-29, 2006.

  20. Adolescent Brain Development: NIMH Study • First large scale longitudinal study • NIMH Child Psychiatry Branch 1989 • Scans children/adolescents at 2 y intervals • Dec ‘05: 4000 scans from 2000 subjects • Source: Lenroot RK. Giedd JN. Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. [Review] [94 refs] Neuroscience & Biobehavioral Reviews. 30(6):718-29, 2006.

  21. Adolescent Brain Development: NIMH Study • Three goals of study • Map developmental trajectories of brain development • Differentiate genetic vs. environmental influences • Use results of study to guide treatment or optimize healthy brain development • Source: Lenroot RK. Giedd JN. Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. [Review] [94 refs] Neuroscience & Biobehavioral Reviews. 30(6):718-29, 2006.

  22. Adolescent Brain Development Dr. Giedd et al. 1999 • Longitudinal study on 145 children/adolescents • Two “waves” of gray matter over-production • Conception to 18 months • Adolescent period Source: Giedd JN, Blumenthal J, Jeffries NO, et al. Brain development during childhood and adolescence: a longitudinal MRI study. Nature Neuroscience, 1999; 2(10): 861-3.

  23. Adolescent Brain Development • Increased cortical gray matter • Extra connections between neurons “arborization” • Maximum thickness at different times • Source: Lenroot RK. Giedd JN, Blumenthal J, Jeffries NO, et al. Brain development during childhood and adolescence: a longitudinal MRI study. Nature Neuroscience, 1999; 2(10): 861-3.

  24. Adolescent Brain Development Late development of prefrontal cortex • Gray matter loss occurs latest in the dorsolateral prefrontal cortex (DLPFC) • Reaches adult levels ~ 20s • Portion of brain involved in higher order cognitive functions Source: Giedd JN. Structural Magnetic Resonance Imaging of the Adolescent Brain. Ann. N.Y. Acad. Sci. 2004; 1021: 77-85

  25. Adolescent Brain Development • Sowell et al. 1999 • Compared brain MRI scans of 23-30 year olds to 12-16 year olds • Areas of frontal lobe showed the largest differences among these two groups Source: Teenage Brain: A work in progress; available at www.nimh.gov

  26. Increased Gray Matter Decreased Gray Matter More Efficient Connections Pruning Genetics Environment

  27. Example of Genes vs. Environment Cerebellum and corpus callosum studies in twins • Corpus callosum very similar (genetics) • Cerebellum different (environment) Source: Interview with Jay Giedd, Inside the Teenage Brain, Frontline PBS, available at www.pbs.org

  28. Alcohol Use in Adolescence • Alcohol kills  6.5 times more individuals under age 21 than all other drugs combined (The National Institute of Alcoholism and Alcohol Abuse) •  25% of all underage drinkers meet the criteria for abuse or dependence (The National Center on Addiction and Substance Abuse at Columbia University)

  29. Arizona Youth Survey 2006Arizona Criminal Justice Commission • Average age of first alcohol use 12.84 vs. regular alcohol use 14.21 • Reduction in alcohol use in all grades compared to 2004 survey • Decreased 1.5 to 3.4% in each grade for lifetime • Decreased 1.2 to 4.1% in each grade for 30 day

  30. Adolescence and Drug Use • Different response to alcohol during this developmental period • Sensitivity to rewards different than adults • Frontal lobe developing at a time when humans most likely to experiment with drugs

  31. Rat Studies Compared to adults, adolescents experienced: • Increased brain damage after 4 day binge drinking • Increased memory impairment • Less sedation • Less motor impairment Source: Aaron White, Rethinking underage drinking -- What does science have to say about it?www.science-says.com, Nov 2006

  32. Human Studies Tapert et al., 2002 • Neuropsychological functioning and substance use involvement over 8 year period in 16-24 yo • Cumulative levels of alcohol and other drug use correlated with impairments in verbal learning and memory • Heavy drinking was associated with attention deficits • Experiencing withdrawal from alcohol predicted visuospatial deficits Source: Tapert SF. Granholm E. Leedy NG. Brown SA. Substance use and withdrawal: neuropsychological functioning over 8 years in youth. Journal of the International Neuropsychological Society. 8(7):873-83, 2002 Nov.

  33. Human Studies De Bellis et al., 2000 • Hippocampus smaller in adolescents who abused alcohol • Amount of hippocampal damage correlated with the number of years of alcohol abuse Source: De Bellis MD. Clark DB. Beers SR. Soloff PH. Boring AM. Hall J. Kersh A. Keshavan MS. Hippocampal volume in adolescent-onset alcohol use disorders.[see comment]. American Journal of Psychiatry. 157(5):737-44, 2000 May.

  34. Risk Factors Family History Peer alcohol use Temperament and personality Childhood behavior problems Family factors Protective Factors Temperament Religiosity Parenting factors Adolescent Drinking: Risk and Protective Factors Source: Windle M. Spear LP. Fuligni AJ. Angold A. Brown JD. Pine D. Smith GT. Giedd J. Dahl RE. Transitions into underage and problem drinking: developmental processes and mechanisms between 10 and 15 years of age. [Review] [143 refs] Pediatrics. 121 Suppl 4:S273-89, 2008 Apr.

  35. Cautionary Statements • “It is essential to balance the excitement about all the new learning with caution about the limits of understanding” • Jack Shonkoff, interview for “Inside the teenage brain” for PBS frontline • Direct correlations between adolescent brain and behavior changes has not yet been established

  36. Summary • Brain development begins in early gestation and continues into twenties • Major brain restructuring during adolescence includes prefrontal cortex, which is important in executive functioning • Alcohol use during adolescence concerning given ongoing brain development • More longitudinal studies needed to confirm preliminary data

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