By age 6: the brain is 90% to 95% of its adult size.

maximum brain-cell density: occurs between the third and sixth month of gestation

Rapid neural growth occurs: between the ages of 6 and 12

Peak of neural growth: when girls are about 11 and boys 12 ½

Gray matter is thinned out at a rate of about 0.7% a year, tapering off in the early 20s

Cerebellum: area that coordinates both physical and mental activities & is particularly responsive to experience

Regions that reach maturation first: vision, hearing, touch and spatial processing

Brain areas that mature second: areas that coordinate vision, hearing & touch

Last part of brain to form: Prefrontal cortex

Prefrontal cortex: home of the so-called executive functions--planning, setting priorities, organizing thoughts, suppressing impulses, weighing the consequences of one's actions.

Androgens and estrogens: Released as pruning begins; directly influence serotonin and other mood-regulating neurochemicals, especially active in the limbic system

Limbic system: emotional center of the brain

Adolescents engage in high risk behavior, impulse control is not fully formed

MRI: reveals brain structure

FMRI: shows brain activity while subjects are doing assigned tasks

In identifying emotional expressions children and adolescents use more amygdala, while adults use frontal lobe.

Amygdala: a structure in the temporal lobes associated with emotional and gut reactions

Social influences: Teens have higher likelihood of risk behavior when in groups or emotionally charged situations, not after age 20

Abundance in dopamine-rich areas of the brain: an additional factor in teen vulnerability to substance abuse

nucleus accumbens: region in the frontal cortex that directs motivation to seek rewards

Motivation deficit: comes with propensity to engage in high excitement and or low effort behaviors, emphasis immediate payoff for best results

Melatonin levels: take longer to rise in adolescents than children or adults regardless of sun or activities

ADHD and Tourette's syndrome: typically appear by age 7; rapid growth of brain tissue may set the stage for the increase in motor activities and tics, symptoms recede as pruning begins

Schizophrenia: appears about the time the prefrontal cortex is getting pruned; typical cortical gray matter loss is 15% during adolescence, but 25% sometimes in schizophrenia cases.

Emerging adult age: The median onset for anxiety disorders, depression, bipolar disorder, and schizophrenia

Age 25: best estimate for when the brain is truly mature

How to help teens: providing structure, organizing their time, guiding them through tough decisions

Overproduction or Exuberance: considerable thickening of synaptic connections occurs during prenatal development through first 18 months of life, again around ages 10–12 peaking there

Overproduction: occurs in many parts of gray matter, but concentrated in frontal lobes

frontal lobes: involved in most of the higher functions of the brain: planning ahead, solving problems, making moral judgments.

Between the ages of 12 and 20: the average brain loses 7% to 10% of its gray matter

synaptic pruning is especially rapid: among adolescents with high intelligence

Myelination: creation of myelin sheaths

Myelin: a blanket of fat wrapped around the main part of the neuron, serves the function of keeping the brain’s electrical signals on one path and increasing their speed, continues through adolescence

Cerebellum: part of the lower brain, important for mathematics, music, decision making, and even social skills and understanding humor. It continues to grow through adolescence and well into emerging adulthood

the last structure of the brain to stop growing: Cerebellum

How brain structure changes in emerging adulthood: continued myelination, synaptic pruning, and the formation of new connections

gray matter: is composed of brain cells decreases through 20s and 30s

white matter: consists of myelinated axons and other connections between brain cells, increases through pruning until 40 when it declines rapidly

rapid synaptic pruning of the gray matter during emerging adulthood: implicated in the development of schizophrenia, anxiety, and depression