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Adolescent Brain Development
Robert Wm. Blum, MD, MPH, PhD
Johns Hopkins University
Section A
Factors That Contribute to Brain Maturation
Adolescence: Time for Great Risk and Opportunity

It is the stage of life of the greatest risk for:
-  Emergence of psychological disorders
-  Depression, anxiety, conduct disorders (early/mid adolescence)
-  Schizophrenia (late adolescence)
-  Alcohol and drug use (mid/late adolescence)
4
Culture Influences the Timing of Puberty

Monogamous vs. polygamous societies

Presence vs. absence of father

Exposure to pressures
5
Some Developmental Phenomena Occur Cross-Species

Earlier maturation of females

Greater risk taking of males

Change in sleeping patterns

Increased alcohol consumption
6
Epigenetics

Genes and environment interact through epigenetic processes to
influence behavior
7
How Epigenetics Works

Epigenetics controls genetic influence through methylation (-CH3
group) to one of the proteins in DNA sequence, effectively silencing
the gene
-  Genes surrounded by methyl groups are more difficult to
transcribe or copy
8
Example

The role of licking of rat pups by mother in infancy influences
degree of aggressiveness when they mature (Weaver et al., 2004)
9
Genetic Influences on Behaviors

Genetic influences on behaviors tend to increase with age through
adolescence

Verbal skills and cognitive functioning of adopted children become
increasingly more like biologic than adoptive parents during
adolescence
10
Genetic Differences in Brain Development

Female is the “default” pathway for neurodevelopment

Absent of testosterone, female brain development occurs with
syndromes
-  Congenital adrenal hyperplasia
-  Androgenetic sensitivity syndrome
11
Sexual Orientation

Pre- and post-natal hormonal environment of the brain may
influence sexual orientation
-  Congenital adrenal hyperplasia
-  Diethylstilbestrol (DES)
-  Maternal stress
-  Genetics
12
Critical Periods for Male-Typical Sexual Differentiation

Perinatal: gonadal hormones influence sexual differentiation of the
brain

Puberty: rising hormonal levels produce final maturational changes
of the brain
13
Rising Sex Hormones Influence Sexual Interest
Church Going
Testosterone
Source: Urdy, 1985
High
Low
High
2
4
Low
1
3
14
Raging Hormones Is a Myth

Hormones contribute only modestly to adolescent mood

Contributions to negative affect
-  Gonadal hormones: 4%
-  Social factors: 8–18%

Testosterone contributes modestly to male risk-taking
15