Adolescent Brain Development

1. Adolescent Brain Development

2. I will send you this presentation jburkmd@roadrunner.com you will see this slide again at the end

3. Old View of Brain Development • Brain is a finished product by age 12 – an inexperienced adult brain • Most important change in adolescence is stimulation by sex hormones resulting in irritability (girls) and aggression (boys) • Formal operations, age 12, was highest cognitive development • Cerebellum is for motor function

4. Logical Ramifications of Old View • Could be held accountable as an adult • Could be taught how to avoid danger • Given information, could weigh risks and benefits of decisions like an adult • By age 12, the brain was not vulnerable to developmental insult

5. Laws reflect this thinking • Can join the military at age 18 without parental consent • Can be tried “as an adult” in serious crimes as young as 14 (or younger) • Can operate a motor vehicle at 16 without adult supervision • (US drinking age 21 is an anomaly) • (Must be 25 to rent a car – what’s up with that?)

6. Health policy reflects this thinking • To combat HIV, teen pregnancy give information, condoms, training in the use of condoms • To combat youth smoking, drugs, alcohol give information • To combat teen motor vehicle fatalities, give information and training • Minors can consent to controversial treatment

7. Education reflects this thinking Focus on delivering more information, not brain development When budgets are crunched, cut out music, art, physical education (High School day start at 7AM)

8. Social norms reflect this thinking • Unsupervised children over 12 are accepted • Parents/caregivers expect “good” kids to behave “responsibly” • Deaths due to poor judgment in intact adolescents are called “accidental”

9. What does science tell us about the adolescent brain?

10. Life Course of Brain Development • Maximum brain cell density achieved by second trimester in utero – culminating an explosive period of prenatal neural growth • Dramatic pruning eliminates unnecessary brain cells during third trimester (autism may be the result of insufficient or abnormal prenatal pruning)

11. Life Course of Brain Development • Dramatic increase in brain size in early childhood – 90-95% adult size by age 6 • Thickening myelin sheaths make faster, more efficient connections • Myelinization proceeds through age ?40

12. Second wave of proliferation… • Between age 6 and 12, neurons grow “bushier” with new dendritic connections causing thickening of gray matter • Peak occurs for girls age 11, boys 12.5 • (not new cells) (1)

13. …followed by pruning • After peaking in volume, gray matter is thinned at 0.7% per year – 15% loss total • Pruning tapers off in the early 20s • Pruning is probably guided both by genetics and by “use” (1)

14. There is a temporal sequence Prefrontal Cortex, home of the “executive functions,” is pruned and shaped late

15. Functional Brain Anatomy • Prefrontal Cortex • Medial Temporal Lobe/Limbic System/Amygdala • Basal Ganglia/Striatal Cortex/Nucleus Accumbens • Corpus Callosum • Cerebellum

16. Terminology • Central Sulcus • Frontal Lobe • Precentral Gyrus (primary motor cortex) • Prefrontal cortex

17. Prefrontal Cortex

18. Prefrontal Cortex-Executive Functions • Planning • Setting priorities • Organizing thoughts • Suppressing impulses • Weighing consequences

19. Most Important Idea Today Adolescent brain development is characterized by “frontalization”- increasing metabolism in, organization of and reliance upon the frontal lobes over time… not completed until the early twenties. (2,3)

20. Emerging Adulthood • Age 18-25 • Jeffrey Arnett American Psychologist 2000 • …emergence of complex forms of thinking required in complex societies.

21. PUBERTY

22. Time course of Puberty • Girls – onset between 10 and 11, completed between 15-17 • Boys –onset between 11 and 12, completed between 16-17

24. Role of hormones • Brain development proceeds independent of timing of puberty • Sex hormones attach to receptors and directly affect serotonin and other neurochemicals that regulate mood and excitability • Sex hormones are especially active in the limbic system, driving emotionality

25. Functional Brain Anatomy • Prefrontal Cortex • Medial Temporal Lobe/Limbic System/Amygdala • Basal Ganglia/Striatal Cortex/Nucleus Accumbens • Corpus Callosum • Cerebellum

26. Medial Temporal Lobe/Limbic System/Amygdala The limbic system consists of the primary olfactory cortex, hippocampus (primitive cortex on the medial surface of the temporal lobes) and the amygdala – The amygdala (which is almond shaped) is the nucleus in the brain responsible for the primitive impulses –fear, anger and aggression

27. Limbic System

29. Hippocampus

30. Adolescents and the Amygdala Functional MRI of kids and adults, and kids over time, attempting to identify emotions displayed in photographs of faces showed: Kids under 14 make mistakes- see anger Kids utilize the amygdala more than the frontal lobe 3. Over time kids utilize the frontal lobe more (5)

31. The pleasure center… …or the story of the rat in the maze…

32. Nucleus Accumbens • Formerly known as the pleasure center or the reward center – the MOTIVATOR • Activated by dopamine • Final common pathway of all addictions – indeed, all voluntary “seeking” behavior

33. Functional Brain Anatomy • Prefrontal Cortex • Medial Temporal Lobe/Limbic System/Amygdala • Basal Ganglia/Striatal Cortex/Nucleus Accumbens • Corpus Callosum • Cerebellum

34. Basal Ganglia • Five subcortical nuclei • Includes the caudate, putamen and globus pallidus which are called the corpus striatum • Corpus striatum is functionally divided into the dorsal striatum and the ventral striatum • The ventral striatum includes the ventral caudate, putamen, and the nucleus accumbens septi

35. Cortex Basal Ganglia Midbrain Pons, Cerebellum

37. Basal Ganglia

38. The adolescent and the nucleus accumbens Lower activity on functional scans in adolescents

39. The Adolescent and the Nucleus Accumbens In the rat, levels of dopamine receptors in the striatum increase dramatically during an age range that falls with the window of periadolescent development. (7)

40. A state of dopamine deficiency • May partly explain adolescent tendencies toward boredom, short-sighted decision-making, inability to delay gratification, etc. • May make adolescents particularly vulnerable to addiction • May drive pleasure or thrill seeking

41. Functional Brain Anatomy • Prefrontal Cortex • Medial Temporal Lobe/Limbic System/Amygdala • Basal Ganglia/Striatal Cortex/Nucleus Accumbens • Corpus Callosum • Cerebellum

42. Corpus Callosum

43. Corpus Callosum

44. Corpus Callosum Thick bundle of axons that allows the two cerebral hemispheres to communicate with one another- thought to be involved with problem solving and creativity

45. Corpus Callosum in Adolescence During adolescence, the nerve fibers thicken and process information more and more efficiently(1)

46. Functional Brain Anatomy • Prefrontal Cortex • Medial Temporal Lobe/Limbic System/Amygdala • Basal Ganglia/Striatal Cortex/Nucleus Accumbens • Corpus Callosum • Cerebellum

47. Cerebellum Long thought to play a role in physical coordination, this area may also regulate certain thought processes. More sensitive to environment than to heredity, the cerebellum supports mathematics, music and advanced social skills.

48. Cerebellum

49. Cerebellum in Adolescence New research shows that it changes dramatically during adolescence, increasing the number of neurons and the complexity of their connections. The cerebellum is the only part of the brain that continues growing well into the early twenties (8)

50. Review-Summary of New View of Brain Development in Adolescence • Preadolescent growth in gray matter • Adolescent “pruning” • Prolonged process of frontal lobe maturation • Increased Myelinization • Hormones • Shift from the Amygdala to the frontal lobes • Nucleus Accumbens “deficiency” • Increase connections of the brain hemispheres • Importance of the cerebellum