Chapter Five Development and Plasticity of the Brain

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Chapter Five Development and Plasticity of the
Brain
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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Growth and Differentiation of the Brain
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
2 of 33

• CNS begins to form when embryo is two weeks old
• By 7 weeks the hindbrain, midbrain and forebrain
  are differentiated
• At birth, brain weighs 350g
• About 9 months after birth the prefrontal cortex
  is developed enough for child to achieve object
  permanence
• At end of first year brain weighs 1000 grams,
  close to adult weight of 1200-1400 grams

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Figure 5.3
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
3 of 33

• Figure 5.3  Human brain at five stages of
  development. The brain already shows an adult
  structure at birth, although it continues to grow
  during the first year or so.

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Growth and Development of Neurons
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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• Proliferation cells in ventricles divide
• some stay as stem cells
• some become primitive neurons and glia that go to
  new destination
• Migration cells follow chemical path toward
  final destination
• Gene or poison that interferes with proliferation
  and migration can produce mental retardation

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Growth and Development of Neurons cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
5 of 33

• Differentiation axons and dendrites are formed
  while migrating
• Myelination addition of insulating sheath that
  speeds transmission (still forming up to 20 years
  of age)
• Synaptogenesis formation of synapses continues
  throughout life

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Determinants of Neuron Survival
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
6 of 33

• We produce more neurons than we need, probably to
  be sure that there are enough for each receiving
  cell
• Survival requires two conditions
• must form synapse with target cell and receive a
  nerve growth factor (a neurotrophin) from that
  cell
• must also be stimulated to release
  neurotransmitters into synapse
• Apoptosis programmed cell death that occurs when
  synapses receive little NGF
• Competition among neurons for survival is a
  selection process that has been termed neural
  Darwinism

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Chemical Pathfinding by Axons
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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• Axons seek specific connections
• Weiss (1924) axons from normal leg branched to
  corresponding muscles of grafted leg
• Sperry (1943) cut axons from optic nerve to
  tectum and rotated eye of newt, but axons
  returned to their original site (newt saw world
  upside down and backwards)
• Axons follow chemical gradients
• In newt, protein (TOPDV) is concentrated more in
  the dorsal than ventral retina, and more in the
  ventral than dorsal tectum
• axons from retina follow paths to sites on tectum
  with similar TOPDV concentrations

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Figure 5.8
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
8 of 33

• Figure 5.8 Retinal axons match up with neurons in
  the tectum by following two gradients. The
  protein TOPDV is concentrated mostly in the
  dorsal retina and the ventral tectum. Axons rich
  in TOPDV attach to tectal neurons that are also
  rich in that chemical. Similarly, a second
  protein directs axons from the posterior retina
  to the rostral portion of the tectum.

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Fine-Tuning by Experience
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
9 of 33

• Experience alters dendritic branching
• enriched environments, exercise increases
  branching and develops thicker cortex
• education correlated with branching, but they
  interact

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Generation of New Neurons
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
10 of 33

• Human olfactory receptors replenished from supply
  of immature cells
• Birds replace specific cells
• songbirds periodically replace cells used in
  singing
• chickadee grows new neurons in hippocampus each
  summer to remember where seed is stored
• Still not clear that adult primates, e.g.,
  humans, monkeys, can form new neurons

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Effects of Experience on Human Brain Structure
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
11 of 33

• Professional musicians have enlarged area in
  temporal cortex of right hemisphere
• Extensive experience with stringed instruments
  enlarges and reorganizes area of post central
  gyrus devoted to left fingers
• In extreme cases neuronal reorganization can
  cause musicians cramp
• Experience and chemical effects can combine
• Ex in prenatal environment retinal activity
  simultaneously activates adjacent cells
• output is sent to lateral geniculate cells which
  select groups of adjacent axons and become
  responsive to them

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Proportional Growth of Brain Areas
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
12 of 33

• Size of one area proportional to others (except
  olfactory bulb is smaller in humans)
• human brain structure nearly the same as other
  mammals and similar to all vertebrates
• primates have larger cerebral cortex in
  proportion to rest of brain

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Proportional Growth of Brain Areas cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
13 of 33

• Brain structure related to way of life
• Ex monkeys swing through trees and so have
  larger brain representation of their forearm
  muscles
• Brain structure depends on length of
  embryological development and number of neurons
  produced per day

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The Vulnerable Developing Brain
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
14 of 33

• Developing brain more vulnerable to effects of
  malnutrition, toxic chemicals and infections
• anesthesia can kill neurons in infants
• child of diabetic mother may have long-term
  attention and memory problems
• Fetal alcohol syndrome at birth
• severe health and mental health problems, e.g.,
  heart defects, facial abnormalities,
  hyperactivity and depression
• neurons received fewer neurotrophins, resulting
  in increased apoptosis

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The Vulnerable Developing Brain cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
15 of 33

• Fetal cocaine exposure
• decrease in IQ and language skills
• Fetal smoking exposure
• low birth weight
• long term intellectual defects
• crib death
• impairments of immune system
• ADHD

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Causes of Human Brain Damage
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
16 of 33

• Closed head injury (CHI) sudden trauma that does
  not puncture the brain, e.g., an automobile
  accident or assault
• results from rotational forces driving brain into
  skull or blood clots that interrupt blood flow
• repeated blows, e.g., from boxing, can cause loss
  of memory and loss of movement control

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Different Brain Injuries CNN Today Biological
Psychology, Volume I
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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Causes of Human Brain Damage cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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• Stroke ischemia or hemorrhage causing a loss of
  normal blood flow to a brain area
• a chain of chemical events results in
  accumulation of sodium, calcium and zinc ions
  inside neurons, causing cell death

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Figure 5.20
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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• Figure 5.20  Mechanisms of neuron death after
  stroke. Procedures that can preserve neurons
  include removing the blood clot (immediately),
  blocking excitatory synapses, stimulating
  inhibitory synapses, blocking the flow of calcium
  and zinc and cooling the brain.

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Treatment for Stroke Patients CNN Today
Biological Psychology, Volume I
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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Reducing Harm from a Stroke
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
21 of 33

• For ischemia, tissue plasminogen activator (tPA)
  breaks up blood clots
• One promising drug opens potassium channels,
  reducing overstimulation
• Most effective lab method is to cool the brain
• cooling human brain for three days improves
  survival and behavioral functioning

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Effects of Age on Recovery
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
22 of 33

• Recovery generally better if damage occurs at
  younger age
• younger rats with amygdala damage recover quicker
• after one hemisphere of rat is removed, the other
  increases in thickness
• 2-year old child with left cerebral damage will
  develop some speech but adult would not recover
  much language
• But, young brain is also more vulnerable
• in rats, after removal of the anterior portion of
  the infant cortex, the posterior portion develops
  less than normal

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Mechanisms of Recovery After Brain Damage
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
23 of 33

• Learned adjustments in behavior
• patients find it easier to accept impairment but
  do better when therapy encourages recovery
• monkey found it easier to do without one
  deafferented limb, but when two were cut then
  monkey learned to reuse both

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Mechanisms of Recovery After Brain Damage cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
24 of 33

• Stimulants paired with physical therapy enhanced
  recovery of stroke victims suffering from
  diaschisis, the decreased activity of surviving
  neurons
• Regrowth of axons
• Crushed, but not cut, axons in peripheral CNS can
  regrow but may reattach to wrong muscle
• CNS and peripheral axons regrow in fish
• scar tissue and astrocytes and myelin secrete
  proteins that inhibit growth in humans

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Mechanisms of Recovery After Brain Damage cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
25 of 33

• Collateral sprouting nearby surviving neurons
  grow new branches to replace synapses left vacant
  by a damaged axon
• Denervation or disuse supersensitivity
• after the destruction or inactivity of an
  incoming axon, the postsynaptic cell becomes more
  sensitive to a neurotransmitter
• remaining neurons also increase release of
  neurotransmitter
• can lead to recovery of near normal functions

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Figure 5.25
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
26 of 33

• Figure 5.25  Collateral sprouting. A surviving
  axon grows a new branch to replace the synapses
  left vacant by a damaged axon.

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Figure 5.27
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
27 of 33

• Figure 5.27  Demonstration of denervation
  supersensitivity. Injecting 6-OHDA destroys axons
  that release dopamine on one side of the brain.
  Later amphetamine stimulates only the intact side
  of the brain because axons that release dopamine
  are damaged on one side. Apomorphine stimulates
  the damaged side more strongly because it
  directly stimulates dopamine receptors, which
  have become supersensitive on that side.

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Reorganized Sensory Representations and Phantom
Limb
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
28 of 33

• Amputated 3rd finger in owl monkey led to cortex
  responding to 2nd and 4th fingers
• Monkey lost sensory input from limb
• 12 years later sprouts from facial axons on
  several levels of CNS filled vacant synapses
• limb was felt when face was touched.
• Same experience in human patients because arm and
  head near each other in cortex and in the spinal
  cord
• note that use of artificial limb dissipates
  phantom sensations

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Behavioral Interventions
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
29 of 33

• Current emphasis is on supervised practice of
  impaired skills
• Positive reinforcement therapy helps develop
  socially acceptable behavior for persons with
  frontal lobe therapy
• Research suggests therapists remove distracting
  stimuli and help person develop remaining skills
• rat with visual cortex lesion can relearn old
  skills and eventually new ones
• rat with visual cortex damage can learn quicker
  when irrelevant stimuli were not present

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Figure 5.31
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
30 of 33

• Figure 5.31  Memory impairment after cortical
  damage. Brain damage impairs retrieval of a
  memory but does not destroy it completely.
  (Source Based on T.E LeVere Morlock, 1973).

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Drugs
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
31 of 33

• Nimodipine (calcium blocker) improved memory on
  visual learning tasks
• in rats with visual cortex lesions
• Gangliosides (carbohydrate and fat molecules)
  help restore damaged brains
• through unknown mechanisms
• Women with brain injury recover better than men
  and especially if the damage occurs when
  progesterone levels were high

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Brain Grafts
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
32 of 33

• Neural transplants have been tried to treat
  Parkinsons disease
• Difficulties include finding suitable donor cells
• Currently experimental

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Transplant Therapy for Brain Tumors CNN Today
Biological Psychology, Volume I
James W. Kalat
Biological Psychology, 8th Edition
Chapter 5 Development and Plasticity of the
Brain
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