Life-Span Development of the Brain and Behavior

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Life-Span Development of the Brain and Behavior
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7 Life-Span Development of the Brain and Behavior

• Growth and Development of the Brain Are Orderly
  Processes.
• Development of the Nervous System Can Be Divided
  into Six Distinct Stages
• Glial Cells Provide Myelin, Which Is Vital for
  Brain Function
• Genes Interact with Experience to Guide Brain
  Development ( ????????????)

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7 Life-Span Development of the Brain and Behavior

• Experience Is an Important Influence on
  Development
• Developmental Disorders of the Brain Impair
  Behavior
• The Brain Continues to Change As We Grow Older
• Two Timescales Are Needed to Describe Brain
  Development

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7 Growth and Development of the Brain Are
Orderly Processes

• The mature human brain has about 100 billion
  neurons. (1 ??)
• The developing nervous system relies on genetic
  information and its environment.
• One measure of brain development is brain weight.

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Figure 7.1 Human Brain Weight as a Function of
Age
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7 Growth and Development of the Brain Are
Orderly Processes

• A zygote is a fertilized egg.
• A human embryo will develop three cell layers
• Ectoderm outer layer, becomes the nervous
  system
• The neural groove forms between ridges of the
  ectoderm.

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Figure 7.2 Development of the Nervous System in
the Human Embryo and Fetus (Part 1)
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Figure 7.2 Development of the Nervous System in
the Human Embryo and Fetus (Part 2)
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7 Growth and Development of the Brain Are
Orderly Processes

• The neural tube forms from the neural ridges.
• The anterior part of the neural tube has three
  subdivisions - the forebrain, the midbrain, and
  the hindbrain.
• A developing human is called an embryo for the
  first 10 weeks, then a fetus.

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Figure 7.2 Development of the Nervous System in
the Human Embryo and Fetus (Part 3)
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Figure 7.2 Development of the Nervous System in
the Human Embryo and Fetus (Part 4)
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Figure 7.2 Development of the Nervous System in
the Human Embryo and Fetus (Part 5)
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

1. Neurogenesis mitosis produces neurons
2. Cell migration cells move to establish distinct
   populations
3. Differentiation cells become distinctive
   neurons or glial cells

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

1. Synaptogenesis establishment of synaptic
   connections
2. Neuronal cell death selective death of some
   nerve cells
3. Synapse rearrangement loss or development of
   synapses, fine-tuning

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Figure 7.3 The Six Stages of Neural Development
(Part 1)
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Figure 7.3 The Six Stages of Neural Development
(Part 2)
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Figure 7.3 The Six Stages of Neural Development
(Part 3)
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Figure 7.3 The Six Stages of Neural Development
(Part 4)
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Figure 7.3 The Six Stages of Neural Development
(Part 5)
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Figure 7.3 The Six Stages of Neural Development
(Part 6)
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Neurogenesis is the production of nerve cells.
• Nonneural cells divide through mitosis and form
  the ventricular zone.
• Cells leave the ventricular zone and become
  either neurons or glial cells.

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Figure 7.4 The Proliferation of Cellular
Precursors of Neurons and Glial Cells (Part 1)
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Figure 7.4 The Proliferation of Cellular
Precursors of Neurons and Glial Cells (Part 2)
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• In C. elegans researchers can follow the
  development of every neuron the cell fate is
  highly determined.
• In vertebrates, development is shaped by
  cell-cell interactions, and is less predetermined.

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Figure 7.5 Cell Fate in a Simple Organism (Part
2)
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• During cell migration cells move away from
  the ventricular layer.
• Radial glial cells act as guides for cells to
  migrate along.
• Cell adhesion molecules (CAMs) promote adhesion
  of parts of the nervous system to guide cells.

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Figure 7.6 Glial Spokes Guide Migrating Cells
(Part 1)
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• When cells reach their destinations they begin to
  express genes to make the proteins they need.
• This cell differentiation allows a cell to
  acquire its specific appearance and function.

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Figure 7.7 Cerebral Cortex Tissue in the Early
Development of Humans
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Two classes of influences on differentiation
• Cell-autonomous independent of other cells and
  driven by genes, intrinsic organization as seen
  in vitro
• Neural environment cells are affected by the
  influence of other cells

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Figure 7.8 The Development of Purkinje Cells in
the Human Cerebellum
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• An injured nerve cell responds in different ways
• Retrograde degeneration destruction of the cell
  after an injury close to the cell body
• Former target cells of that neuron may show
  transneuronal degeneration.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Anterograde degeneration or Wallerian
  degeneration loss of the distal portion of an
  axon after an injury to the axon
• The axon may regrow, especially in the peripheral
  nervous system guided by CAMs.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Q How do cells know they should be expressed as
  motor neurons in the spinal cord?
• Cells in the notochord release a protein (sonic
  hedgehog) that directs some cells in the spinal
  cord to become motoneurons.
• Induction is the influence of one set of cells on
  the fate of nearby cells.

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Figure 7.9 The Induction of Spinal Motoneurons
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Cells differentiate into the appropriate cell
  type for their location.
• Regulation is the response to cell injury in
  development other cells will develop and take
  its place.
• Stem cells are undifferentiated cells that can
  assume a new cell fate.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Brain cells change early in life through
• Process outgrowth the growth of axons and
  dendrites
• Synaptogensis formation of synapses
• Extensions emerge from growth cones at the tips
  of axons and dendrites.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Filopodia are the fine outgrowths of growth cones
  and lamellipodia are sheetlike extensions.
• Both adhere to the environment and pull the
  growth cone in a particular direction.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Axons are guided by chemicals released by the
  target cells.
• Chemoattractants are chemical signals that
  attract certain growth cones.
• Chemorepellents repel growth cones.

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Figure 7.10 The Growth Cones of Growing Axons
and Dendrites (Part 3)
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Figure 7.10 The Growth Cones of Growing Axons
and Dendrites (Part 4)
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Synapses form rapidly on dendrites and dendritic
  spines.
• Spines proliferate after birth, and connections
  are affected by experience.
• The nerve cell body increases in volume to
  support the dendritic tree.

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Figure 7.11 The Postnatal Development of
Synapses (Part 1)
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Figure 7.11 The Postnatal Development of
Synapses (Part 2)
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Cell death, or apoptosis, is a normal part of
  development.
• Cells have death genes that are expressed only
  during apoptosis.
• Caspases are a family of proteases that cut up
  proteins and DNA.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Apoptosis starts with a Ca2 influx that causes
  mitochondria to release a protein, Diablo.
• Diablo binds to inhibitors of apoptosis proteins
  (IAPs), which normally inhibit the caspases.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Without IAP inhibition, the caspases are able to
  dismantle the cell.
• Bcl-2 proteins block apoptosis by preventing the
  release of Diablo.

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Figure 7.12 Death Genes Regulate Apoptosis
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Several factors influence cell death in the
  nervous system.
• If the size of the synaptic target is reduced,
  fewer neurons survive.
• Neurons compete for chemicals the target cells
  make, called neurotrophic factors without
  enough, they die.

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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Nerve growth factor (NGF) is produced by targets
  and taken up by the axons of innervating neurons,
  keeping them alive.
• Other factors are brain-derived neurotrophic
  factor (BDNF) and similar members of the
  neurotrophin family.

a spinal motor neuron grown in vitro with NGF ?
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Figure 7.15 A Model for the Action of
Neurotrophic Factors
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• Synapse rearrangement, or synaptic remodeling,
  refines synaptic connections.
• One influence on synaptic survival is neural
  activity.
• A neurotrophic factor may contribute.

The layer of gray matter in the anterior cortex
become thinner (remodeling) along development ?
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7 Development of the Nervous System Can Be
Divided into Six Distinct Stages

• The chemoaffinity hypothesis says each cell has a
  chemical identity to guide development at a
  synapse.
• After injury the brain will try to reestablish
  the original connections.

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7 Glial Cells Provide Myelin, Which is Vital for
Brain Function

• Glial cells are added throughout life.
• Myelination by glial cells increases the rate at
  which axons send messages.
• Multiple sclerosis destroys myelin and disrupts
  sensory and motor function with
  de-synchronization of neural signal transduction.

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7 Genes Interact with Experience to Guide Brain
Development

• Genes are intrinsic factors that influence brain
  development.
• The genotype, or genome, is all of the genetic
  information of an individual.
• The phenotype is all of the physical
  characteristics.

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7 Genes Interact with Experience to Guide Brain
Development

• A mutation is a change in genetic structure.
• Mutants are individuals with altered genes,
  sometimes with differences in behavioral
  phenotype.

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Figure 7.18 Cerebellar Mutants among Mice
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7 Genes Interact with Experience to Guide Brain
Development

• Animals with mutations are important in
  researching development
• Site-directed mutagenesis changes the sequence
  of a nucleotide in a gene
• Knockout organism has a gene disabled
• Transgenic has a new or altered gene

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7 Genes Interact with Experience to Guide Brain
Development

• Clones (??) are genetically identical animals.
• Identifiable neurons Mauthner cells appear in
  some fishes who produce genetically identical
  offspring.

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7 Genes Interact with Experience to Guide Brain
Development

• Animals and humans with identical genes may still
  behave differently.
• Experience causes neurons to change the genes
  they express, according to synaptic stimulation.
• Identical individuals will still have different
  experiences, and thus different behaviors.

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7 Experience Is an Important Influence on Brain
Development

• Visual deprivation can lead to blindness.
• Amblyopia impairment of vision in one eye
  (turned inward or outward) with inability to see
  clear forms (but a double visual image)
• Binocular deprivation no light to both eyes
  produces changes in neurons in the visual cortex.

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7 Experience Is an Important Influence on Brain
Development

• The sensitive period of development is when
  experience or treatment can make permanent
  alterations.
• Monocular deprivation during this period causes
  the deprived eye to not respond in adulthood.

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Figure 7.19 Brain Development in the Visual
Cortex of Cats
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7 Experience Is an Important Influence on Brain
Development

• An ocular dominance histogram shows the response
  of brain neurons to stimuli presented to either
  eye.
• Normally, most cortical neurons respond equally.

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Figure 7.20 Ocular Dominance Histograms (Part 1)
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Figure 7.20 Ocular Dominance Histograms (Part 2)
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Figure 7.20 Ocular Dominance Histograms (Part 4)
Briefly, the eye-cortex connections still
developed but no visual dominance. If prolonged,
total blindness occurs.
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7 Experience Is an Important Influence on Brain
Development

• In development of the visual cortex, axons from
  each eye compete for synaptic targets.
• Hebbian synapses grow stronger or weaker
  depending on their ability to affect a
  postsynaptic cell.

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Figure 7.21 Hebbian Synapses Can Account for
Changes after Monocular Deprivation
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7 Experience Is an Important Influence on Brain
Development

• Early exposure to visual patterns fine-tunes
  connections.
• Visual experience during the critical early
  period modifies responses in the visual cortex.
• Visual experience in every day life affects our
  perception. (next frame for demonstration)

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Figure 7.22 Which Line is More Slanted?
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7 Developmental Disorders of the Brain Impair
Behavior

• Hypoxia is a transient lack of oxygen can occur
  at birth.
• Phenylketonuria (PKU), a disorder of protein
  metabolism, is the absence of an enyzme that
  metabolizes phenylalanine in foods.
• These can result in retardation.

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7 Developmental Disorders of the Brain Impair
Behavior

• Down syndrome is a chromosomal abnormality the
  inheritance of an extra chromosome 21.
• Fragile X syndrome results from inheriting extra
  trinucleotide repeats (CGG), repetitions of
  nucleotides, in the same gene.

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7 Developmental Disorders of the Brain Impair
Behavior

• Prenatal exposure to maternal conditions such as
  viral infection, drug use and malnutrition can
  impair development.
• Behavior teratology studies behavioral
  impairments.

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7 Developmental Disorders of the Brain Impair
Behavior

• Fetal alcohol syndrome (FAS) occurs in 40 of
  children born to alcoholic mothers.
• FAS results in anatomical changes to the face,
  mental retardation, and other neurological
  deficits.
• Children may lack a corpus callosum.

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Figure 7.24 Abnormal Brain Development Associated
with Fetal Alcohol Syndrome
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7 Developmental Disorders of the Brain Impair
Behavior

• Attention deficit hyperactivity disorder (ADHD)
  has three core symptoms
• Distractibility, hyperactivity, and impulsiveness
• ADHD brains may differ in volume, and in the
  prefrontal cortex and the cerebellum.

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7 Developmental Disorders of the Brain Impair
Behavior

• Autism is characterized by impaired social
  interactions and language.
• Children may perseverate, showing a behavior
  repeatedly.
• There are structural differences in the brain,
  including the amygdala which is associated with
  fear.
• People with autism may be unable to empathize
  with others.
• They have difficulty trying to mimic movements or
  facial expressions.
• There is low activation of a frontal cortex area
  containing mirror neurons.

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Figure 7.25 Underactivation of Mirror Cells in
Autism
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Figure 7.25 Underactivation of Mirror Cells in
Autism (Part 2)
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Figure 7.25 Underactivation of Mirror Cells in
Autism (Part 3)
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7 Developmental Disorders of the Brain Impair
Behavior

• Aspergers syndrome also called
  high-functioning autism.
• Children with Aspergers do not lose their
  language capabilities.
• They do have difficulty interpreting emotional
  facial expressions in others.

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7 The Brain Continues to Change As We Grow Older

• Memory impairment correlates with shrinkage of
  the hippocampus.
• Immediate memory does not decline, while delayed
  memory does correlated with hippocampal volume.
• In motor cortex Betz cells show a reduction after
  age 50, yet inferior olive cells do not change
  with age.

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Figure 7.26 Hippocampal Shrinkage Correlates
with Memory Decline in Aging
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7 The Brain Continues to Change As We Grow Older

• Dementia is a drastic failure of cognitive
  ability.
• Alzheimers disease is a form of senile dementia.
  
• It begins as memory loss of recent events
  brains show reduced metabolism and cortical
  atrophy.

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Figure 7.27 Patients with Alzheimers Show
Reduced Activity in the Brain
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7 The Brain Continues to Change As We Grow Older

• Alzheimers produces cellular changes
• Senile plaques form by ß-amyloid buildup, also
  called amyloid plaques
• Neurofibrillary tangles, including the tau
  protein, occur
• Basal forebrain nuclei disappear

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Figure 7.28 Patients with Alzheimers Show
Structural Changes in the Brain
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7 The Brain Continues to Change As We Grow Older

• ß-amyloid buildup occurs when amyloid precursor
  protein (APP) is cleaved by two enzymes
• ß -secretase and presenilin
• ß-amyloid breakdown is done by apolipoprotein
  (ApoE).
• Gene mutations in these proteins are associated
  with Alzheimers.

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Figure 7.29 One Hypothesis of Alzheimers Disease
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7 Two Timescales Are Needed to Describe Brain
Development

• Evolution has produced genes with a basic plan
  for development.
• Cell-cell interactions during that development
  adjust the fate of individual cells.
• Ultimately, sensory experience affects neuronal
  survival.