1. The Neurobiology of AdolescentThe Neurobiology of Adolescent
DevelopmentDevelopment
Carlo Carandang, MDCarlo Carandang, MD
Assistant ProfessorAssistant Professor,,
Division of Child Psychiatry, DalhousieDivision of Child Psychiatry, Dalhousie
UniversityUniversity
Attending Child PsychiatristAttending Child Psychiatrist,,
IWK Health CentreIWK Health Centre
Halifax, Nova Scotia, CanadaHalifax, Nova Scotia, Canada

2. ObjectivesObjectives
 Learn about adolescent developmentLearn about adolescent development
 Correlate adolescent development withCorrelate adolescent development with
brain changesbrain changes
 Learn about the two distinct processes ofLearn about the two distinct processes of
behavioral maturation (adolescence) andbehavioral maturation (adolescence) and
gonadal maturation (puberty), and howgonadal maturation (puberty), and how
both interact, with resulting mature,both interact, with resulting mature,
reproductively active adultreproductively active adult

3. Adolescent Development:Adolescent Development:
DefinitionsDefinitions
 Adolescence: maturation of adult socialAdolescence: maturation of adult social
and cognitive behaviors (behavioraland cognitive behaviors (behavioral
maturation)maturation)
 Puberty: activation of the hypothalamic-Puberty: activation of the hypothalamic-
pituitary-gonadal axis that culminates inpituitary-gonadal axis that culminates in
gonadal maturationgonadal maturation

4. Behavioral and GonadalBehavioral and Gonadal
MaturationMaturation
 Two distinct brain-driven processesTwo distinct brain-driven processes
 Separate timingSeparate timing
 Dynamically coupled via interactions between theDynamically coupled via interactions between the
nervous system and gonadal steroid hormonesnervous system and gonadal steroid hormones
 Endpoint of these two processes is the reproductivelyEndpoint of these two processes is the reproductively
mature adultmature adult
 Old-school: puberty viewed purely from endocrineOld-school: puberty viewed purely from endocrine
perspectiveperspective
 New school: neural control of hormone secretion andNew school: neural control of hormone secretion and
experience of adolescence affecting brain processesexperience of adolescence affecting brain processes

5. Part I: Adolescent Brain DevelopmentPart I: Adolescent Brain Development
(Behavioral Maturation)(Behavioral Maturation)

6. Adolescent DevelopmentAdolescent Development
 AdolescenceAdolescence
 Transition from childhood to adulthoodTransition from childhood to adulthood
 Acquires independent living skillsAcquires independent living skills
 Adolescent ‘angst’Adolescent ‘angst’
 Changes in mood, attitude, sleep, diet, weight,Changes in mood, attitude, sleep, diet, weight,
and apathy/anhedoniaand apathy/anhedonia
 This is normal and crucial processThis is normal and crucial process
 Don’t confuse with DepressionDon’t confuse with Depression
 Depression is debilitating…adolescent angst isDepression is debilitating…adolescent angst is
developmental progressdevelopmental progress

7. Changes in Brain Function duringChanges in Brain Function during
AdolescenceAdolescence
 Recent research has shown that changesRecent research has shown that changes
in brain function may underlie thein brain function may underlie the
behavioral changes in adolescentsbehavioral changes in adolescents

8. Importance of AdolescenceImportance of Adolescence
 Not all animals pass through adolescenceNot all animals pass through adolescence
 Some animals are born independentSome animals are born independent
 Positives: do not require an extendedPositives: do not require an extended
nurturing; find own food; no competition withnurturing; find own food; no competition with
siblingssiblings
 Negatives: born with all the instruction theyNegatives: born with all the instruction they
will ever have to survive; not able to adapt towill ever have to survive; not able to adapt to
major changes in the environmentmajor changes in the environment
 Brain says eat green bugs, and green bugsBrain says eat green bugs, and green bugs
are wiped out, then big trouble!are wiped out, then big trouble!

9. Human AdolescenceHuman Adolescence
 Born with ability to adapt to changes inBorn with ability to adapt to changes in
their environmenttheir environment
 DrawbackDrawback
 Flexibility to adapt comes at a priceFlexibility to adapt comes at a price
 Humans born completely dependent on othersHumans born completely dependent on others

10. Development from Childhood toDevelopment from Childhood to
AdulthoodAdulthood
 11stst
decade of life spent exploring the worlddecade of life spent exploring the world
within the context of supportive familywithin the context of supportive family
 22ndnd
decade of life (adolescence) spentdecade of life (adolescence) spent
venturing away from family into the deeperventuring away from family into the deeper
end of the gene pool, to create ownend of the gene pool, to create own
familiesfamilies

11. Changing Adolescent BehaviorChanging Adolescent Behavior
 Increase time with peersIncrease time with peers
 Adaptive: learning social skillsAdaptive: learning social skills
 Increase risk-takingIncrease risk-taking
 Adaptive: need to explore the environment andAdaptive: need to explore the environment and
venture away from the comforts of family…otherwise,venture away from the comforts of family…otherwise,
the teen is content just to stay at homethe teen is content just to stay at home
 Increase conflicts with authorityIncrease conflicts with authority
 Adaptive: conflict with adults helps teens find theyAdaptive: conflict with adults helps teens find they
own paths; not necessarily adaptive for teens to takeown paths; not necessarily adaptive for teens to take
on the traits of the adults around themon the traits of the adults around them

12. Changing Adolescent BehaviorChanging Adolescent Behavior
 Changes in sleep patternsChanges in sleep patterns
 Teens stay up later and wake up later, and have lessTeens stay up later and wake up later, and have less
restful sleeprestful sleep
 Unsure how this is adaptiveUnsure how this is adaptive
 Decreased satisfaction with daily lifeDecreased satisfaction with daily life
 Teens=boredom/apathyTeens=boredom/apathy
 Adaptive: when boredom is combined with increasedAdaptive: when boredom is combined with increased
risk-taking, helps teen to venture outrisk-taking, helps teen to venture out
 PubertyPuberty
 Hormonal and physical changes that prepares theHormonal and physical changes that prepares the
teen for procreation and physical confrontationteen for procreation and physical confrontation

13. Brain Development DuringBrain Development During
AdolescenceAdolescence
 Changes in behavior from childhood toChanges in behavior from childhood to
adolescence accompanied by changes inadolescence accompanied by changes in
brain functionbrain function
 Adolescent brain is more moldable byAdolescent brain is more moldable by
experience than the adult brainexperience than the adult brain
 Can’t teach an old dog new tricksCan’t teach an old dog new tricks

14. Neurobiology of Early DevelopmentNeurobiology of Early Development
 From the womb to late childhood, there isFrom the womb to late childhood, there is
overproduction of neuronal tissueoverproduction of neuronal tissue
 Peak synaptogenesis in the frontal cortex beginsPeak synaptogenesis in the frontal cortex begins
in 8th postnatal mo. maximum at 2 yrs. of age;in 8th postnatal mo. maximum at 2 yrs. of age;
corresponds temporally to emergence of skilledcorresponds temporally to emergence of skilled
actions & cognitive functionsactions & cognitive functions
 From birth to 4From birth to 4thth
yr., brain volume quadruples,yr., brain volume quadruples,
cortical synapse counts double, dendriticcortical synapse counts double, dendritic
arbours quadruple, volume of cortical pyramidalarbours quadruple, volume of cortical pyramidal
cells double or quadruple depending on regioncells double or quadruple depending on region
and layerand layer
 Slower cortical growth in middle childhoodSlower cortical growth in middle childhood

15. Shaping of the Brain ThroughShaping of the Brain Through
ExperienceExperience
 By adulthood, we lose about half of the neurons weBy adulthood, we lose about half of the neurons we
are born withare born with
 Neurons making contacts with other neuronsNeurons making contacts with other neurons
survive, while those that don’t die (neuronsurvive, while those that don’t die (neuron
elimination)elimination)
 Mediated by neurotrophic factorsMediated by neurotrophic factors
 Circuits that are used repeatedly will grow healthyCircuits that are used repeatedly will grow healthy
and complex, while underutilized ones wither awayand complex, while underutilized ones wither away
 Hence, interactions with outside world shapes theHence, interactions with outside world shapes the
child’s brain, and allows us to adapt to changes inchild’s brain, and allows us to adapt to changes in
the environment, unlike other animalsthe environment, unlike other animals

16. Shaping of the Brain ThroughShaping of the Brain Through
ExperienceExperience
 Experience also affects the synapses at the tipsExperience also affects the synapses at the tips
of the neurons, via pruningof the neurons, via pruning
 Neuron elimination takes place mostly prenatallyNeuron elimination takes place mostly prenatally
 Synapse elimination (pruning) occurs throughoutSynapse elimination (pruning) occurs throughout
childhood and in adolescencechildhood and in adolescence
 Followed by a much slower decline in synapticFollowed by a much slower decline in synaptic
density during the adult yearsdensity during the adult years
 Depending on cortical region, max. synapticDepending on cortical region, max. synaptic
density at 1.4 to 4.4 yrs. of age;density at 1.4 to 4.4 yrs. of age;
 Adult synaptic density= 60% of the max.Adult synaptic density= 60% of the max.

17. Postnatal changes in number of dendritic spines of largePostnatal changes in number of dendritic spines of large
pyramidal neurons of the layer IIIc of the human prefrontalpyramidal neurons of the layer IIIc of the human prefrontal
cortex. Solid line shows the number of spines within the initialcortex. Solid line shows the number of spines within the initial
200 pm segment of the apical dendrite, while the dashed line200 pm segment of the apical dendrite, while the dashed line
shows the number of spines within the initial 50 pm segment ofshows the number of spines within the initial 50 pm segment of
the basal dendrite. N = newborn; M = months; Y = years.the basal dendrite. N = newborn; M = months; Y = years.

18. Neurobiology of DevelopmentNeurobiology of Development
Virtually every aspect of early human development,Virtually every aspect of early human development,
from the evolving brain circuitry to the emergingfrom the evolving brain circuitry to the emerging
capacity of the child to master motor skills, solvecapacity of the child to master motor skills, solve
cognitive problems and experience empathy, iscognitive problems and experience empathy, is
affected by the cumulative influences of lifeaffected by the cumulative influences of life
experienceexperience
nature…nutrition…prenatal & postnatal environment…nature…nutrition…prenatal & postnatal environment…
attachments & relationships… education… culture…attachments & relationships… education… culture…
Environment can hinder development just as it canEnvironment can hinder development just as it can
promote it.promote it.
Concept of critical periodsConcept of critical periods

19. Epigenetic PerspectiveEpigenetic Perspective
 Epigenetics:Epigenetics: the interactions of genesthe interactions of genes
with their environment that bring thewith their environment that bring the
phenotype into beingphenotype into being
 Cortical development is of anCortical development is of an
epigenetic natureepigenetic nature
 Basically, brain development is brought aboutBasically, brain development is brought about
via interactions of genes with environmentvia interactions of genes with environment

20. Epigenetic PerspectiveEpigenetic Perspective
 Organism evolves in a constant interactionOrganism evolves in a constant interaction
between genes and environmentbetween genes and environment
 About 70% of genes are involved in CNSAbout 70% of genes are involved in CNS
developmentdevelopment
 Evidence that brain structures and amount ofEvidence that brain structures and amount of
gray matter under some but not total geneticgray matter under some but not total genetic
controlcontrol
 Evolutionary design for maximal adaptability toEvolutionary design for maximal adaptability to
environment (plasticity)environment (plasticity)

21. Neurobiology of Adolescent BrainNeurobiology of Adolescent Brain
DevelopmentDevelopment
 Adolescent brain development not anAdolescent brain development not an
extension of childhood brain developmentextension of childhood brain development
 Novel changes in adolescents:Novel changes in adolescents:
 Frontal lobe gray matter volumes increaseFrontal lobe gray matter volumes increase
until peak at age 12, then decline throughoutuntil peak at age 12, then decline throughout
adolescenceadolescence
 Frontal lobe circuits which are exercised areFrontal lobe circuits which are exercised are
strengthened while the others are prunedstrengthened while the others are pruned

22. Neurobiology of Adolescent BrainNeurobiology of Adolescent Brain
DevelopmentDevelopment
 During adolescence, energy required by theDuring adolescence, energy required by the
frontal lobes begins to decrease and reachesfrontal lobes begins to decrease and reaches
adult levels by 16-18adult levels by 16-18
 With decreasing frontal volume and decreasingWith decreasing frontal volume and decreasing
energy requirements, frontal lobe activity duringenergy requirements, frontal lobe activity during
certain tasks becomes more focused andcertain tasks becomes more focused and
efficientefficient
 Hence, the adolescent developmental task ofHence, the adolescent developmental task of
acquiring good impulse control and goodacquiring good impulse control and good
decision-making is correlated with changes indecision-making is correlated with changes in
the frontal lobesthe frontal lobes

23. FrontalisationFrontalisation
 The frontal lobes take an increasingly importantThe frontal lobes take an increasingly important
role in guiding behavior and controlling activity inrole in guiding behavior and controlling activity in
other parts of the brainother parts of the brain
 Frontalisation continues throughout adolescenceFrontalisation continues throughout adolescence
 Neurobiological explanation for a teen’s drive forNeurobiological explanation for a teen’s drive for
taking risks and novelty-seeking (adaptivetaking risks and novelty-seeking (adaptive
behavior), and their poor impulse control andbehavior), and their poor impulse control and
poor decision-making (skill-deficit…lack ofpoor decision-making (skill-deficit…lack of
frontalisation)frontalisation)
 Teens: all gas, and no brakes!Teens: all gas, and no brakes!

24. Other Changes in the AdolescentOther Changes in the Adolescent
BrainBrain
 Parietal lobes peak in gray matter volume at ageParietal lobes peak in gray matter volume at age
11 and decrease throughout adolescence11 and decrease throughout adolescence
 Processing sensory info and spatial relationshipsProcessing sensory info and spatial relationships
 Occipital lobes increase throughout adolescenceOccipital lobes increase throughout adolescence
and early 20sand early 20s
 Visual informationVisual information
 Temporal lobes reach maximum at 16-17Temporal lobes reach maximum at 16-17
 Memory, visual, auditoryMemory, visual, auditory

25. Other Changes in the AdolescentOther Changes in the Adolescent
BrainBrain
 Corpus callosum increases in size duringCorpus callosum increases in size during
adolescenceadolescence
 Communication between both sides of theCommunication between both sides of the
brainbrain
 Neurotransmitters and receptorsNeurotransmitters and receptors
 As compared to adult brains, neurotransmittersAs compared to adult brains, neurotransmitters
and receptors are expressed at their highestand receptors are expressed at their highest
levels in the immature brain, often in totallylevels in the immature brain, often in totally
different anatomical regions, and often withoutdifferent anatomical regions, and often without
mature synapsesmature synapses

26. Part II: Gonadal MaturationPart II: Gonadal Maturation

27. Gonadal MaturationGonadal Maturation
 Tendency in the culture to ascribe every negative teenTendency in the culture to ascribe every negative teen
moment to “hormones”moment to “hormones”
 Brain changes described earlier relieves hormones ofBrain changes described earlier relieves hormones of
much of the blamemuch of the blame
 Start of puberty begins by the brain signaling theStart of puberty begins by the brain signaling the
hypothalamus to secrete gonadotropin releasinghypothalamus to secrete gonadotropin releasing
hormone (GRH) to produce luteinizing hormone (LH) andhormone (GRH) to produce luteinizing hormone (LH) and
follicle stimulating hormone (FSH), which in turn affectsfollicle stimulating hormone (FSH), which in turn affects
the gonads to produce estrogen and testosterone, withthe gonads to produce estrogen and testosterone, with
resultant physical changes in reproductive systemresultant physical changes in reproductive system
 Breast and genital development, hair growth, deepening voice,Breast and genital development, hair growth, deepening voice,
etc.etc.

28. Behaviors and Sex HormonesBehaviors and Sex Hormones
 Hormones not responsible for your teen not ableHormones not responsible for your teen not able
to bear your singing in the morningto bear your singing in the morning
 Hormones most likely responsible for your teen’sHormones most likely responsible for your teen’s
fixation on sex and social standingfixation on sex and social standing
 Adolescent males; “Will this lead to sex?”Adolescent males; “Will this lead to sex?”
 Adolescent females; “How will this affect my standingAdolescent females; “How will this affect my standing
in the group?”in the group?”
 Beyond these 2 behavioral domains, hormonesBeyond these 2 behavioral domains, hormones
do not affect much outside these realmsdo not affect much outside these realms
 Give hormones a break!Give hormones a break!

29. Sex Hormones interacting withSex Hormones interacting with
BrainBrain
 Testosterone swell the teenage amygdalaTestosterone swell the teenage amygdala
 Amygdala can be blamed for the slammedAmygdala can be blamed for the slammed
doors and sudden tears in teens, whodoors and sudden tears in teens, who
previously had sunny dispositions aspreviously had sunny dispositions as
childrenchildren

30. Temporal Dissociations Between GonadalTemporal Dissociations Between Gonadal
Maturation and Adolescent Brain DevelopmentMaturation and Adolescent Brain Development
 Eating disorders and excessive exercise significantlyEating disorders and excessive exercise significantly
delay gonadal maturationdelay gonadal maturation
 Animal models predict that steroid hormones have differentAnimal models predict that steroid hormones have different
influences on a brain that has already developedinfluences on a brain that has already developed
 At the other extreme, precocious puberty results in theAt the other extreme, precocious puberty results in the
exposure of the childhood brain to steroid hormonesexposure of the childhood brain to steroid hormones
prematurelyprematurely
 Animal models predict that this alters the developmentalAnimal models predict that this alters the developmental
trajectory of the braintrajectory of the brain
 Evolutionary significance: variations in the temporalEvolutionary significance: variations in the temporal
sequence most likely contributes to the individualsequence most likely contributes to the individual
differences in adult behavior and risk for sex-baseddifferences in adult behavior and risk for sex-based
psychopathologiespsychopathologies

31. Other Hormones Affecting TeenOther Hormones Affecting Teen
BehaviorsBehaviors
 When compared to adults, teens have later secretion ofWhen compared to adults, teens have later secretion of
melatonin, and it lasts longer into the day and nightmelatonin, and it lasts longer into the day and night
 As a result, teens sleep later, and wake up later whenAs a result, teens sleep later, and wake up later when
compared to adultscompared to adults
 Teens sleep patterns dictated by adult schedules,Teens sleep patterns dictated by adult schedules,
leading to chronic state of sleep deprivationleading to chronic state of sleep deprivation
 Memory and concentration problemsMemory and concentration problems
 Increased risk for depressionIncreased risk for depression
 Best that parents can do is to encourage teens to slow-Best that parents can do is to encourage teens to slow-
down at night, avoid caffeine in the home, and let thedown at night, avoid caffeine in the home, and let the
teens catch up on the weekendsteens catch up on the weekends
 Schools should adapt more to teen schedulesSchools should adapt more to teen schedules

32. Other Brain Changes inOther Brain Changes in
AdolescentsAdolescents
 Adolescent brains less active than adultsAdolescent brains less active than adults
in those regions of the brain that motivatein those regions of the brain that motivate
reward-based behaviorreward-based behavior
 Teen brains also have increased levels ofTeen brains also have increased levels of
dopamine, a neurotransmitter associateddopamine, a neurotransmitter associated
with pleasure, which may increase thewith pleasure, which may increase the
need for pleasure seekingneed for pleasure seeking

33. ConclusionsConclusions
 Changes in brain function most likely contribute to theChanges in brain function most likely contribute to the
behaviors exhibited by adolescents, and the environmentbehaviors exhibited by adolescents, and the environment
in turn shapes and molds the developing adolescentin turn shapes and molds the developing adolescent
brainbrain
 Adolescent behaviors are adaptive, which help the teenAdolescent behaviors are adaptive, which help the teen
develop the skills to survive and become independentdevelop the skills to survive and become independent
beingsbeings
 Neurobiology of adolescent development is not simply aNeurobiology of adolescent development is not simply a
continuation of childhood developmentcontinuation of childhood development
 Behavioral and gonadal maturation are dynamicallyBehavioral and gonadal maturation are dynamically
coupled via interactions between the nervous systemcoupled via interactions between the nervous system
and gonadal steroid hormones; endpoint of these twoand gonadal steroid hormones; endpoint of these two
processes is the reproductively mature adultprocesses is the reproductively mature adult

34. Take Home Message to ImpartTake Home Message to Impart
to Parentsto Parents
 Your patience, understanding, and guidance isYour patience, understanding, and guidance is
needed for your teen, even when your teenneeded for your teen, even when your teen
vehemently opposes youvehemently opposes you
 Teen brains need help with organizationalTeen brains need help with organizational
problemsproblems
 They need help to make social, political, andThey need help to make social, political, and
moral judgmentsmoral judgments
 They need help to anticipate potentialThey need help to anticipate potential
consequences of their actionsconsequences of their actions
 They need help to channel their risk-taking thatThey need help to channel their risk-taking that
does not affect their health or hurt othersdoes not affect their health or hurt others