Brain Development Stages

Why This Matters

Brain development isn't just a biology topic—it's the foundation for understanding why children think, learn, and behave differently at various ages. When you're answering questions about cognitive development, language acquisition, or adolescent risk-taking, you're really being tested on whether you understand the underlying neural changes driving those behaviors. The stages of brain development explain everything from why toddlers learn languages so easily to why teenagers struggle with impulse control.

This topic connects directly to major course themes: nature versus nurture, critical periods, cognitive development theories, and individual differences. You'll see these concepts appear in questions about Piaget's stages, attachment formation, and even abnormal psychology. Don't just memorize the sequence of brain changes—know what each stage enables developmentally and what happens when it goes wrong. That's what earns you points on FRQs.

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Early Structural Formation

The brain's physical architecture forms first, establishing the basic structures that everything else builds upon. These prenatal processes create the neural tube that becomes your entire central nervous system.

Neurulation

• Neural plate formation begins days after conception—this flat sheet of cells is the earliest precursor to your entire nervous system
• Folding creates the neural tube by week 3-4, establishing the structure that differentiates into brain and spinal cord
• Defects during this stage cause serious conditions like spina bifida and anencephaly, making prenatal nutrition (especially folic acid) critical

Neural Tube Formation

• Closure occurs around week 4 of embryonic development—the tube must seal completely at both ends for normal development
• Regional differentiation begins immediately as different sections become the forebrain, midbrain, hindbrain, and spinal cord
• Failure to close properly is one of the most common birth defects, occurring before many women know they're pregnant

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Building the Neural Network

Once structures exist, the brain populates them with neurons and connections. This is where the raw material for all future learning and behavior gets created.

Neurogenesis

• Peak neuron production occurs prenatally—you're born with most of the neurons you'll ever have (roughly 100 billion)
• Limited neurogenesis continues in the hippocampus throughout life, which is significant for memory formation and learning
• Environmental factors matter—stress hormones can reduce neurogenesis while enriched environments and exercise can enhance it

Synaptogenesis

• Explosive synapse formation peaks in early childhood—infants form up to 1 million new synaptic connections per second
• Experience-dependent process means enriched environments literally build more connected brains
• Overproduction is intentional—the brain creates far more synapses than it needs, setting up the pruning process that follows

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Refinement and Efficiency

The brain shifts from building to optimizing—eliminating unnecessary connections while strengthening important ones. This is the neural basis for the "use it or lose it" principle.

Pruning

• Synaptic pruning eliminates 40-50% of synapses during childhood and adolescence, following the principle that unused connections are removed
• Experience determines what stays—repeatedly activated neural pathways strengthen while neglected ones disappear
• Abnormal pruning patterns are associated with neurodevelopmental disorders including schizophrenia (excessive pruning) and autism spectrum disorder (insufficient pruning)

Myelination

• Myelin sheaths increase neural transmission speed by up to 100x—this fatty coating acts as insulation around axons
• Follows a back-to-front pattern in the brain, with sensory and motor areas myelinating before the prefrontal cortex
• Continues into the mid-20s, explaining why adolescents have adult-level raw intelligence but not adult-level processing efficiency

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Specialized Development

Different brain regions mature at different rates and develop specialized functions. This uneven development explains many age-related behavioral patterns.

Lateralization

• Hemisphere specialization emerges in early childhood—the left hemisphere typically dominates for language and logical processing, the right for spatial and emotional processing
• Not absolute—both hemispheres contribute to most tasks, and the corpus callosum enables constant communication
• Influenced by both genetics and experience—handedness, language exposure, and even musical training affect lateralization patterns

Prefrontal Cortex Development

• Last brain region to fully mature, not completing development until the mid-20s
• Controls executive functions—planning, impulse control, decision-making, and social judgment
• Explains adolescent behavior patterns—the limbic system (emotion/reward) matures before the prefrontal cortex can regulate it, creating a "gas pedal without brakes" situation

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Windows of Opportunity

The brain's receptivity to experience changes over time, with some periods offering unique learning opportunities. These concepts explain why timing matters in development.

Critical Periods

• Time-limited windows when specific experiences must occur for normal development—miss the window, and certain abilities may never fully develop
• Classic examples include vision (if one eye is deprived of input early, that eye's cortical connections are permanently weakened) and first language acquisition (native-level phoneme discrimination requires early exposure)
• Sensitive periods are a related but less rigid concept—optimal but not absolutely required timing for development

Plasticity

• The brain's ability to reorganize and form new connections in response to experience, learning, or injury
• Highest during early development but continues throughout life—adult brains can still learn and recover from damage
• Two types matter for exams: experience-expectant plasticity (brain expects certain universal experiences) vs. experience-dependent plasticity (brain adapts to individual-specific experiences)

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Quick Reference Table

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Self-Check Questions

1. Which two processes work together to make the brain more efficient during childhood and adolescence, and how do their mechanisms differ?

2. A child raised in a severely neglected environment shows permanent language deficits despite later intervention. Which concept best explains this outcome, and what related concept explains why some recovery was still possible?

3. Compare synaptogenesis and pruning: How do these processes reflect the "nature versus nurture" debate in brain development?

4. Why do adolescents often show poor impulse control despite having adult-level intelligence? Identify the specific brain development pattern responsible and explain the timing mismatch involved.

5. An FRQ asks you to explain why early intervention programs for children with developmental delays are more effective than later interventions. Which three brain development concepts would you use to build your argument?