Brain development

• Brain


  • Plastic
  • Living organ
  • Changes all the time due to response to its genetic program and environment
• Neurodevelopment


  1. Begins with a single fertilized egg cell

  2. Ends with a functional adult brain

  3. Five phases: neural plate induction, neural proliferation, migration and aggregation, axon growth and synapses formation, neuron death and synapse rearrangement
• Neural plate


  A small patch of ectodermal tissue on the dorsal surface of the developing embryo, destined to develop into the human nervous system
• Stem cells


  Cells of the neural plate that have an almost unlimited capacity for self-renewal and the ability to develop into many different kinds of cells
• Neural tube development


  1. Develops into the cerebral ventricles and spinal cord

  2. Forebrain, midbrain, and hindbrain develop from 3 swellings
• Neural proliferation


  Cells in the neural tube begin to proliferate, with most cell division occurring in the ventricular zone
• Migration


  1. Radial migration - from ventricular zone outward

  2. Tangential migration - parallel to tube walls

  3. Somal translocation and glia-mediated migration
• Aggregation


  Migrating neurons align themselves with other developing neurons to form nervous system structures, mediated by cell-adhesion molecules and gap junctions
• Axon growth


  Growth cones at the tips of axons and dendrites grow towards their targets, guided by attractive and repulsive signals
• Synapse formation


  Axons establish synapses with appropriate target neurons, dependent on chemical signals and the presence of glial cells
• Neuron death


  Active apoptosis and passive necrosis of neurons, triggered by genetic programs and failure to obtain life-preserving chemicals
• Postnatal growth of the human brain results from synaptogenesis, myelination of axons, and increased branching of dendrites
• Myelination


  Increases the speed of axonal conduction, occurring in a sequence that parallels functional development
• Cortical thinning


  Periods of synaptic and gray matter loss occur at different times in different parts of the brain, progressing from primary sensory and motor areas to association areas
• Prefrontal cortex development


  • Displays the most prolonged period of development, responsible for working memory, planning, inhibition, and social behavior
• Young humans do not demonstrate prefrontal cortex-dependent cognitive functions until that region's development has progressed
• Perseveration


  Tendency to continue making a formerly correct response when it is currently incorrect, due to underdeveloped prefrontal cortex
• Permissive experiences


  Allow the expression and maintenance of information in genetic programs of brain development
• Instructive experiences


  Contribute to the information in genetic programs and influence the course of development
• Critical period


  Experience must occur within a particular interval to influence development
• Sensitive period


  Experience has a great effect on development when it occurs during a particular interval, but can still have weak effects outside
• Sensory deprivation leads to fewer synapses and dendritic spines in the primary visual cortex, and deficits in depth and pattern vision
• Enriched environments have beneficial effects, leading to thicker cortices with more dendritic spines and synapses per neuron
• Neurogenesis (the growth of new neurons) occurs in the adult striatum, hippocampus, and olfactory bulbs, but not in other brain regions
• Adult-generated neurons


  Become integrated into neural circuits and conduct neural signals, serving as interneurons in the olfactory bulb and striatum, and granule cells in the hippocampus
• Pattern separation


  Our ability to separate distinct percepts into individual memories for storage, facilitated by adult hippocampal neurogenesis
• Exploration has a greater influence on adult hippocampal neurogenesis than physical activity
• Experience in adulthood can lead to reorganization of sensory and motor cortical maps, and the brain acquires the ability to adapt more effectively to the same conditions in the future