Ch. 7 Infant, Child & Adolescent Brain

32 question-and-answer flashcards summarizing key facts about early brain growth, critical periods, adolescence, plasticity, and their implications.

What is the average weight of a newborn human brain?

About 370 grams (≈13 ounces, slightly less than a pound).

Approximately how heavy is an adult human brain and how many neurons does it contain?

About 3 pounds with roughly 86 billion neurons.

Immediately after birth, how fast does an infant’s whole brain grow?

About 1 percent in volume per day.

By three months of age, what is the brain’s daily growth rate reduced to?

Roughly 0.4 percent per day.

After 90 days, how much larger is a baby’s brain volume compared with birth?

About 64 percent larger.

Which brain region grows the fastest during the first three months and what is its primary role?

The cerebellum; it supports learning motor skills and movements.

During the first three months, by what percentage does the number of cortical neurons increase?

By about 23–30 percent.

What processes make the brain’s white matter look white?

Myelination of axons by oligodendrocytes.

By what age has a child’s brain reached roughly 90 percent of its adult size?

By about 5 years old.

How does a two-year-old’s synapse count compare with an adult’s?

It has about 50 percent more synapses, even though the brain is only ~80 percent adult size.

What is synaptic pruning and why is it important?

The elimination of weaker synapses to strengthen frequently used connections, saving energy and refining circuits.

Compared with many other animals, why are humans born with relatively immature brains?

Extended postnatal development allows greater shaping by environment and experience.

During critical periods, what factors work together to shape neural circuits?

Both genes and environmental experiences.

What two cellular events accompany critical periods of high learning?

Neuronal cell death and synaptic pruning.

What is competitive elimination and when is it especially active?

It is synaptic pruning where stronger connections outcompete weaker ones, especially active during adolescence.

Which brain lobes show the greatest increase in myelination during adolescence?

The frontal lobes.

Why is adolescence often called a second “critical period”?

Because higher-order brain functions are still maturing and are highly influenced by experience.

Which structure shows marked white-matter growth in adolescence and what might this support?

The corpus callosum; it may support enhanced learning by improving inter-hemispheric communication.

Why does adolescent brain development increase risk-taking and susceptibility to addiction?

Changes in reward systems and an immature balance between frontal (control) and limbic (emotion/reward) regions.

What brain changes are linked to adolescent alcohol abuse?

Reduced gray-matter volume, lower white-matter integrity, decreased brain activity, and poorer cognitive performance.

At roughly what age does neuroscience suggest the human brain completes its major development?

Around 30 years old.

Which cortical area shows gray-matter density increases up to age 30 and what functions does it support?

The left temporal lobe; it supports memory and language.

Where is myelination most prominent earlier in life, and where does it increase closer to age 30?

Early: visual, auditory, and limbic cortices; Later: frontal and parietal neocortices.

Name three executive functions associated with the frontal lobe that mature late.

Attention, response inhibition, and long-range planning (also emotion regulation and organization).

Define neural plasticity.

The brain’s ability to modify its structure and function in response to experience and environment.

What is experience-expectant plasticity?

Integration of universal environmental stimuli (e.g., language, faces) during critical periods to guide normal development.

Give an animal example illustrating experience-expectant plasticity.

Finches that do not hear adult songs before sexual maturation fail to learn typical songs.

What is experience-dependent plasticity?

Brain changes driven by individual, non-universal experiences throughout life, without a strict critical period.

Provide a human example of experience-dependent plasticity.

String musicians often have enlarged cortical representation for the fingers of their left hand.

Which imaging technique lets scientists watch living neurons change after specific experiences?

Two-photon imaging.

Why are longitudinal studies valuable in developmental neuroscience?

They track individuals over time, revealing how early events and environments influence later outcomes.

How might understanding plasticity lead to new therapies?

Manipulating adult plasticity (via drugs or circuit-rewiring therapies) could repair disorders rooted in mistimed critical periods.