Neurodevelopment and Neuropsychology

Development

Importance of Development to Neuropsychology

  • Understanding development is essential to neuropsychology because:

    • It is insufficient to consider only the mature adult brain.

    • The adult brain's characteristics are the result of extensive developmental changes over time.

    • A comprehensive understanding of adult neuropsychology rfequires knowledge of developments that occur across the lifespan.

Brain Development Overview

  • The human brain develops from a single cell into a complex structure consisting of billions of neurons.

    • Inquiry: How does this development occur?

Genetic Foundations of Brain Development

  • Genes play a crucial role in determining brain structure and function.

    • The human genome outlines the design of the brain:

    • How does this genetic specification work?

    • DNA contains approximately 20,000 to 25,000 genes.

    • Notably, humans and mice possess the same amount of DNA; however,

    • Mice have fewer than 1/1000th the number of neurons compared to humans.

    • Definition: Genes are not a precise "blueprint" for building a human being, highlighting that no singular gene (or group of genes) solely dictates the formation of specific body parts such as the hand.

Mechanisms of Gene Function in Brain Development

  • Query: How can such a limited number of genes elaborate into a fully functional brain?

    • Explanation:

    • Genes may exhibit multiple functions.

    • Example:

      • Billions of pyramidal cells exist in the cortex, yet the same small set of genes likely orchestrates their development.

    • Development is a progressive process influenced by epigenetic factors.

Central Nervous System Development

Two Levels of CNS Development

  • The development of the CNS is analyzed from two perspectives:

    • Macroscopic

    • Microscopic

Macroscopic Development

  • Definition: Involves the overall development and morphogenesis of the entire brain.

Stages of Development

  • The developmental stages can be categorized into:

    • Prenatal Period

    • Zygotic stage: 0-14 days

    • Embryonic stage: 14 days to 9 weeks

    • Fetal stage: 9 weeks to 40 weeks

    • Postnatal Period

    • Neonate: Birth to 1 month

    • Infant: 1 month to 1 year

    • Childhood: 1 year to 10 years

    • Adolescence: 11 years to 18 years

Overview of Prenatal Development

  • Embryonic Development:

    • Key processes involve:

    • Ectoderm, Endoderm, and Mesoderm formation.

      • Ectoderm gives rise to:

      • Central nervous system.

      • Peripheral nervous system.

      • Epidermis.

      • Hair & mammary glands.

      • Mesoderm leads to:

      • Skeletal muscle and skeleton.

      • Dermis of the skin.

      • Connective tissues.

      • Urogenital system.

      • Heart and blood circulation.

      • Endoderm forms:

      • Digestive tract, liver, kidneys, and lung tissues.

Embryonic Stage Specifics

  • Key developmental processes include:

    • Gastrulation:

    • Cells migrate inward within the embryo, leading to the formation of three distinct germ layers: Endoderm, Mesoderm, and Ectoderm.

  • Organogenesis:

    • Formation of various organs from the three germ layers.

    • Neurulation:

      • The ectoderm evolves into the nervous system, starting during the 3rd week of development.

      • Involves two main parts:

      • Primary (brain development)

      • Secondary (spinal cord formation)

Phases of Neurulation

  1. Induction:

    • Growth factors (e.g., BMP4) initiate cellular differentiation.

  2. Morphological Changes:

    • Cells change shape (e.g., apical constriction), which is crucial for the formation of the neural tube.

  3. Folding:

    • Structural folding occurs as part of neural tube formation, leading to brain and spinal cord development.

Microscopic Level

Neuron Development and Placement (Activity Independent)

  1. Proliferation:

    • Cell division primarily via mitosis.

    • Accompanied by oscillations between different zones of the neural tube.

  2. Migration:

    • Neurons travel to their designated locations through radial glial cells.

  3. Aggregation:

    • Neurons group into clusters or specific structures.

  4. Differentiation:

    • Involves development of the cell body, neuron death, process formation, and synapse formation; primarily activity-dependent.

Differentiation Process in Neurons

  • Stages of Differentiation include:

    1. Formation of the cell body.

    2. Cell death (apoptosis).

    3. Process formation (such as axons).

    4. Formation of synapses, typically influenced by neuronal activity.

Epigenesis in Neural Development

  • Neural epigenesis refers to the dynamic changes in neural structures and connections influenced by genetic and environmental factors.

  • Key concepts include selective stabilization, cell death, and transient redundancy in neuron populations.

Synaptic Density Over Development

  • Synapse density varies with age, as illustrated in a graph showing mean synaptic density in the auditory, visual, and prefrontal cortex areas from newborn to adulthood.

  • Graphically represented data highlight significant changes in synaptic density across different ages:

    • Newborn to adolescence: Rapid increases in synapses.

    • Post-adolescence: Stabilization of synaptic structures.

Summary

  • Development plays a crucial role in neuropsychology, with a necessity to consider both prenatal and postnatal stages to fully comprehend neuropsychological outcomes.

  • The genetic framework, cellular mechanisms, and developmental processes are key to understanding the complexities of the human brain's evolution from fetal stages to complex adult structures.