NSCI 140 - Neuroplasticity & Development, Nature & Nurture (Modules 5-6)

What is the key distinction between a critical period and a sensitive period in brain development?

• Critical period: An exclusive time window — if the expected experience doesn't occur during this window, the developmental change cannot happen later.

• Sensitive period: A preferential time window — the experience has the greatest effect during this period, but weaker effects can still occur outside of it.

Both refer to Experience-Expectant Plasticity (EEP).

What is Experience-Expectant Plasticity (EEP) vs. Experience-Dependent Plasticity (EDP)?

• EEP - Brain expects universal inputs with little variation between individuals; results in consistent neuroanatomical organization

  • eg. light exposure, gravity, basic caregiving

• EDP - Brain shaped by variable, individual experiences; results in unique differences in structure, processes, and skills

  • eg. learning a musical instrument, specific vocabulary, cultural practices

According to Biological Sensitivity to Context Theory (BSCT), what distinguishes "orchid children" from "dandelion children"?

• Orchid Children (~20%) - Highly reactive stress response systems, very sensitive to environmental conditions, show the best or worst outcomes depending on context

• Dandelion Children (~80%) - Minimally reactive stress response systems, resilient; indifferent to external conditions, show average health under most conditions

Key point: Orchid children are more vulnerable to adversity but also benefit the most from enrichment and interventions.

What are Adverse Childhood Experiences (ACEs) and how do the two main types affect brain development differently?

• Deprivation / Neglect - Damages proliferation and pruning of neuronal networks; underdevelopment

• Active Threat / Abuse - Induces fear learning; shortens the period of plasticity

Both disrupt healthy brain development, but through different mechanisms

What is epigenetics and why does it represent a clear interplay between nature and nurture?

• Epigenetics: Changes in gene expression (how DNA is read) — NOT changes to the genetic code itself — in response to life experience.

• Key feature: Epigenetic modifications can be transmitted to subsequent generations (trans-generational epigenetic inheritance).

• This demonstrates that environmental experiences can literally alter how genes function and pass those alterations on.

What is the general principle of hierarchical brain development?

Brain maturation proceeds:

• Bottom to top (brainstem → cortex)

• Back to front (occipital → frontal)

Factors determining maturation timing:

1. Survival urgency — more critical systems mature earlier

2. Phylogenetic age — evolutionarily older structures mature before newer ones

3. Complexity — higher-order integration areas mature later

How does an enriched environment vs. a deprived environment affect neuroplasticity?

• Enriched - Supports both EEP and EDP; greater development of dendrites and synapses

• Normative / Basic - Provides minimum conditions for EEP

• Deprived - Lacks essential stimuli; results in shorter plasticity phase and underdeveloped systems

True or False: Experience-based neuroplasticity can only occur during critical periods of development.

FALSE.

• Critical periods are exclusive windows for some types of EEP.

• Sensitive periods allow plasticity with reduced (but still possible) effects outside the window.

• Experience-Dependent Plasticity (EDP) continues throughout life — it's not limited to specific developmental windows.

What is perceptual narrowing in language development, and when does it occur?

• A shift from language-universal to language-specific phonetic perception.

• Occurs during the first year of life (1st wave of plasticity).

• Part of phonology development and considered an EEP process.

• eg. iWnfants can distinguish all phonetic contrasts at birth but lose sensitivity to non-native contrasts by ~12 months.

Which aspects of language have sensitive periods, and which do not?

Domain Phonology (sound system) Sensitive Period? Yes — strongest in 1st year Type of Plasticity EEP Syntax (grammar rules) Yes — peaks early, declines with age EEP + EDP Semantics/Vocabulary No age constraints Mostly EDP

Key point: Learning new vocabulary can happen throughout life; acquiring native-like accent/grammar is much harder after childhood.

What is the difference between spoken language and written language in terms of plasticity type?

• Spoken language - Experience-Expectant (EEP), A human ability — the brain expects language input

• Written language - Experience-Dependent (EDP), A human invention — requires specific teaching/learning

What was the "old assumption" in neuroscience about the brain, and how has this changed?

• Old assumption - Brain structure is fixed early in life; brain function depends on this fixed structure.

• New understanding - Discoveries of neurogenesis and neuroplasticity across the lifespan show the brain continues to adapt and change based on experience.

• This shifted the debate from "nature vs. nurture" to studying their interaction effects.

Using the card game analogy, how do nature and nurture contribute to neuroplasticity?

• Nature (genetic code) - The cards you're dealt and the rules of the game.

• Nurture (environment) - The dynamics of the game — how you and others play those cards.

Both interact continuously to shape brain development and plasticity.

Why are some brain areas more susceptible to experience-based changes than others?

• Social networks and learning & memory networks show the highest susceptibility to experience-based plasticity.

• Higher-order brain systems show the greatest variability between individuals.

• Lower-level sensory and survival systems are more uniform because they rely on universal (EEP) inputs.

What key insight does trans-generational epigenetic inheritance provide about trauma?

• Environmentally induced changes in gene expression (phenotypes) can persist for several generations.

• Stress and trauma experienced by one generation can be epigenetically transmitted to offspring.

• Example: Studies show descendants of trauma survivors may inherit altered stress response patterns even without direct exposure.