Quiz 4 BNA wk 10

• Brain and behaviour development

  • Rapid
  • Influence each other
• Neuroscientists study the relation between brain and behavioural development from perspectives


  • Structural development correlated with emerging behaviours
  • Behavioural development predicted by underlying neural circuitry
  • Environmental factors influence brain structure, function and behavioural development
• Levels of developmental neuroscience

  • DNA and epigenetics
  • Molecules, synapses, cells
  • Tissue
  • Circuit level
  • Neural systems
  • Behaviour
• Early stages of human embryo development

  1. Fertilisation

  2. Mitotic cell divisions

  3. Blastocyst formation

  4. Implantation

  5. Neural plate formation

  6. Neural tube formation
• Neural tube


  • Forms the central nervous system
  • Has 3 subdivisions at the head end: forebrain, midbrain, hindbrain
  • Open region becomes brain's ventricles and central canal of spinal cord
• Failure of neural tube closure around 3 weeks leads to birth defects
• Prenatal exposures to harmful environmental stimuli

  Alter developmental trajectory of fetal brain
• Teratogens


  Substances that can cause developmental abnormalities in the embryo or fetus
• Folate deficiency can lead to neural tube defects
• Development of the brain between 3 weeks and 3-4 months

  Stages: cell birth, neural migration, cell differentiation, neural maturation, synaptogenesis, neuronal cell death and synaptic pruning, myelogenesis
• Stages of neural development

  • Neural stem cells self-renew and form ventricular zone
  • Neuroblasts migrate out to form cortex
  • Cells differentiate into neurons and glia
• Cortical layers develop from the inside out (layer VI → I)
• At birth, we have most of the neurons we will ever have
• Postnatal brain development


  • Brain weight dramatically increases in first 2 years
  • Neurons begin with simple dendritic structures that become more complex
  • Brain maturation parallels behavioural development
• Increases in brain volume across life are not attributable to increases in neuron numbers
• Order of synaptogenesis across the cortex

  1. Growth burst in auditory and visual cortices from 3-4 months to 1 year

  2. Language areas develop quickly from late infancy to preschool years

  3. Frontal lobe peaks in synaptic density in childhood
• Sensory areas attain peak cortical thickness before areas integrating functions (association areas)
• Blooming and reduction in synaptic density

  Brain growth and selective pruning optimises brain circuits
• Myelination


  • Increases rate at which axons send messages
  • Has big impact on behaviour by allowing rapid communication in neuronal networks
• Types of brain plasticity

  • Experience-independent
  • Experience-expectancy
  • Experience-dependent
• Experience-expectancy plasticity


  • Fine-tuning of brain development based on input from the environment
  • Mostly occurs in early postnatal development
  • Arises from universal sensory inputs from a normal environment
• Experience-dependent plasticity


  • Early stimulating experiences activate and rearrange synapses
  • Neural activity guides synaptic pruning and strengthening of connections
• Molecular events


  • Genes direct newly formed neurons in the fetal brain to their correct location during cell migration
• Early basic wiring of the brain

  Early brain development
• Experience-expectancy plasticity


  Fine-tuning of brain development based on input from the environment, mostly occurs in early postnatal development, arises from universal sensory inputs form a normal environment
• Sensory inputs that form a normal environment


  • Visual stimulation
  • Sound (especially voices)
  • Faces
  • Bodily movement
• Brain expects early stimulating experiences

  Early stimulating experiences activate and rearrange synapses in brain regions involved in senses like vision and hearing as well as language processing, typically experiences enable normal brain development
• Neural activity guides synaptic pruning within brain systems


  1. Redundant or weak synaptic connections are lost

  2. Connections that have adapted to demands of the environment and are used most frequently are strengthened
• There is consistency across individuals in the neuroanatomical structure of many brain regions representing visual and auditory information
• Prevention of perception of expectant experiences

  Stunts or halts development
• Hearing


  • Auditory stimuli early in life is necessary for perception of hearing
  • Deaf subjects exhibited activation in the region of the right auditory cortex when presented with a visual stimulus
  • Visual cortex responds to spoken language in blind children
• Experience-dependent plasticity


  Remodeling of the brain in response to unique life experiences, synapse formation is localised to regions involved in processing specific experiences, synapses can be formed rapidly after some experiences, result of co-activation of two neurons
• Critical periods


  A special subset of sensitive periods involving experience-expectant plasticity, the brain can wire specific skills at an optimum level during different windows of opportunity, critical periods require some experiences to develop or learn a given skill/trait
• Sensitive periods


  More common and extended across development, during these periods an individual is more receptive to particular environmental stimuli
• Lifelong synapse rearrangement is guided by experience
• Conditions related to visual deprivation

  • Blindness
  • Amblyopia: impairment of vision in one eye with inability to see clear forms in some people one eye is misaligned
  • If not realigned in childhood, visual acuity can't be reestablished
• Experiments with lab animals has helped to understand amblyopia and insights into approaches that can reestablish visual acuity
• If vision is impaired in early childhood by cataracts or injury, synaptic connections in the visual cortex are not established and can result in lasting impairments in adulthood
• Evidence for critical periods - visual systems in rats

  1. Monocular deprivation in rats during a critical period leads to a shift in representation in the visual cortex

  2. Deprivation results in a loss of dendritic spines and a reduction in synapses in the visual cortex

  3. The more active inputs of the open eye take over, the closed eye loses its representation, even if the eye is opened later on

  4. If deprivation lasts long enough sight is difficult to restore

  5. Extracellular matrix "nets" mark the ending of critical periods, limit synapse rearrangement once the expected circuit
• Restoring normal vision in rats

  1. Degrading extracellular matrix nets

  2. Environmental enrichment