Download 2605_lect9

BIOPSYCHOLOGY 8e
John P.J. Pinel
Copyright © Pearson Education 2011
Topics
9.1
Phases of Neurodevelopment
9.2
Postnatal Cerebral Development in
Human Infants
9.3
Effects of Experience on the Early
Development, Maintenance, and
Reorganization of Neural Circuits
9.4
Neuroplasticity in Adults
9.5
Disorders of Neurodevelopment:
Autism and Williams Syndrome
Copyright ©
Pearson Education 2011
Neurodevelopment
• Neural Development – an
ongoing process; the
nervous system is plastic
• Experience plays a key
role
• Dire consequences when
something goes wrong
Copyright ©
Pearson Education 2011
The Case of Genie
Illustrates the impact
of severe deprivation
on development
• At age 13, Genie
weighed 62 pounds
and could not chew
solid food
• Beaten, starved,
restrained, kept in a
dark room, denied
normal human
interactions
• Even with special care
and training after her
rescue, her behavior
never became normal
Phases of Development


Ovum + sperm = zygote
Developing neurons accomplish
these things in five phases
 Induction of the neural plate
 Neural proliferation
 Migration and aggregation
 Axon growth and synapse
formation
 Neuron death and synapse
rearrangement
Copyright ©
Pearson Education 2011
Induction of the Neural Plate
• A patch of tissue on the dorsal
surface of the embryo becomes
the neural plate
• Development induced by
chemical signals from the
mesoderm (the “organizer”)
• Visible three weeks after
conception
• Three layers of embryonic cells:
• Ectoderm (outermost)
• Mesoderm (middle)
• Endoderm (innermost)
FIGURE 9.1: How the neural plate develops
Copyright ©
Pearson Education 2011
Neural Proliferation
• Neural plate folds to form the
neural groove, which then fuses
to form the neural tube
• Inside will be the cerebral
ventricles and neural tube
• Neural tube cells proliferate in
species-specific ways: three
swellings at the anterior end in
humans will become the
forebrain, midbrain, and hindbrain
• Proliferation is chemically guided
by the organizer areas – the roof
plate and the floor plate
Copyright ©
Pearson Education 2011
igration
• Once cells have been created through
cell division in the ventricular zone of
the neural tube, they migrate
• Migrating cells are immature, lacking
axons and dendrites
Copyright ©
Pearson Education 2011
Migration

Two types of neural tube
migration



Two methods of migration



Radial migration (moving
out)
Tangential migration (moving
up)
Somal – an extension
develops that leads
migration, cell body follows
Glial-mediated migration –
cell moves along a radial
glial network
Most cells engage in both
types of migration
FIGURE 9.2: Radial Migration and Tangential Migration
Copyright ©
Pearson Education 2011
Migration
FIGURE 9.3: Somal Translocation and Glia-Mediated Migration
Copyright ©
Pearson Education 2011
Neural Crest
• A structure dorsal to the
neural tube and formed from
neural tube cells
• Develops into the cells of the
peripheral nervous system
• Cells migrate long distances
Copyright ©
Pearson Education 2011
Aggregation
• After migration, cells align
themselves with others cells and
form structures
• Cell-adhesion molecules (CAMs):
– Aid both migration and
aggregation
– CAMs recognize and adhere to
molecules
• Gap junctions pass cytoplasm
between cells
– Prevalent in brain development
– May play a role in aggregation
and other processes
Copyright ©
Pearson Education 2011
Axon Growth and Synapse Formation
• Once migration is complete
and structures have formed
(aggregation), axons and
dendrites begin to grow
• Growth cone – at the
growing tip of each
extension, extends and
retracts filopodia as if finding
its way
• Chemoaffinity hypothesis –
postsynaptic targets release
a chemical that guides
axonal growth, but this does
not explain the often
circuitous routes often
observed
Copyright ©
Pearson Education 2011
Axon Growth and Synapse Formation
• Mechanisms underlying axonal
growth are the same across
species
• A series of chemical signals
exist along the way – attracting
and repelling
• Such guidance molecules are
often released by glia
• Adjacent growing axons also
provide signals
FIGURE 9.5: Sperry’s classic
study of eye rotation and
regeneration.
Copyright ©
Pearson Education 2011
Axon Growth and Synapse Formation
• Pioneer growth cones – the
first to travel a route,
interact with guidance
molecules
• Fasciculation – the
tendency of developing
axons to grow along the
paths established by
preceding axons
• Topographic gradient
hypothesis – seeks to
explain topographic maps
FIGURE 9.7: The topographic gradient
hyphothesis
Copyright ©
Pearson Education 2011
Synapse Formation
Formation of new synapses:
• Depends on the presence of glial
cells
• High levels of cholesterol are
needed—supplied by astrocytes
• Chemical signal exchange
between pre- and postsynapctic
neurons is needed
• A variety of signals act on
developing neurons
Copyright ©
Pearson Education 2011
Neuron Death and Synapse Rearrangement
• ~50% more neurons
than arebrain
needed are
The human
produced – death is normal
• Neurons die due to failure to compete for
chemicals provided by targets:
• The more targets, the fewer cell deaths
• Destroying some cells increases
survival rate of remaining cells
• Increasing number of innervating axons
decreases the proportion that survives
Copyright ©
Pearson Education 2011
Life-Preserving Chemicals
• Neurotrophins – promote growth
and survival, guide axons,
stimulate synaptogenesis
• Nerve growth factor (NGF)
• Both passive cell death
(necrosis) and active cell death
(apoptosis)
• Apoptosis is safer than necrosis
– does not promote inflammation
Copyright ©
Pearson Education 2011
Life-Preserving Chemicals
FIGURE 9.8: The effect of neuron death and synapse
rearrangement on the selectivity of synaptic transmission
• Neurons that fail to
establish correct
connections are
particularly likely to die
• Space left after
apoptosis is filled by
sprouting axon
terminals of surviving
neurons
• Ultimately leads to
increased selectivity of
transmission
Copyright ©
Pearson Education 2011
Postnatal Cerebral Development in Human Infants
• Postnatal growth is a
consequence of:
– Synaptogenesis
– Myelination – sensory areas
and then motor areas.
Myelination of prefrontal cortex
continues into adolescence
– Increased dendritic branches
• Overproduction of synapses
may underlie the greater
plasticity of the young brain
Copyright ©
Pearson Education 2011
Development of the Prefrontal
Cortex
• Believed to underlie age-related
changes in cognitive function
• No single theory explains the
function of this area
• Prefrontal cortex plays a role in
working memory, planning and
carrying out sequences of
actions, and inhibiting
inappropriate responses
Effects of Experience on the Early Development,
Maintenance, and Reorganization of Neural Circuits
• Permissive experiences: those that are necessary
for information in genetic programs to be manifested
• Instructive experiences: those that contribute to the
direction of development
• Effects of experience on development are timedependent
• Critical period
• Sensitive period
Copyright ©
Pearson Education 2011
Early Studies of Experience and
Neurodevelopment
• Early visual deprivation
– Fewer synapses and dendritic
spines in primary visual cortex
– Deficits in depth and pattern
vision
•
•Enriched environment
– Thicker cortexes
– Greater dendritic development
– More synapses per neuron
Copyright ©
Pearson Education 2011
Competitive Nature of Experience and
Neurodevelopment
Ocular Dominance Columns
example:
• Monocular deprivation
changes the pattern of
synaptic input into layer IV
of V1 (but not binocular
deprivation)
• Altered exposure during a
sensitive period leads to
reorganization
• Active motor neurons take
precedence over inactive
ones
Copyright ©
Pearson Education 2011
Competitive Nature of Experience and
Neurodevelopment
FIGURE 9.10: The effect of a few days of early monocular deprivation on the structure of axons
projecting from the lateral geniculate nucleus into layer IV of the primary visual cortex. Axons carrying
information from the deprived eye displayed substantially less branching. (Adapted from Antonini &
Stryker, 1993.)
Copyright ©
Pearson Education 2011
Effects of Experience on
Topographic Sensory Cortex Maps
• Cross-modal rewiring
experiments demonstrate the
plasticity of sensory cortexes –
with visual input, the auditory
cortex can see
• Change input, change cortical
topography – shifted auditory
map in prism-exposed owls
• Early music training influences
the organization of human
auditory cortex – fMRI studies
Copyright ©
Pearson Education 2011
Experience Fine-Tunes Neurodevelopment
• Neural activity regulates
the expression of genes
that direct the synthesis
of CAMs
• Neural activity influences
the release of
neurotrophins
• Some neural circuits are
spontaneously active and
this activity is needed for
normal development
Copyright ©
Pearson Education 2011
Neuroplasticity in Adults
• The brain changes and
adapts
• Neurogenesis (growth of new
neurons) seen in olfactory
bulbs and hippocampuses of
adult mammals'—adult
neural stem cells created in
the epedymal layer lining in
ventricles and adjacent
tissues
• Enriched environments and
exercise can promote
neurogenesis
Copyright ©
Pearson Education 2011
Effects of Experience on the Reorganization of the Adult
Cortex
• Tinnitus (ringing in the ears) – produces major
reorganization of primary auditory cortex
• Adult musicians who play instruments fingered by left
hand have an enlarged representation of the hand in
the right somatosensory cortex
• Skill training leads to reorganization of motor cortex
Copyright ©
Pearson Education 2011
Disorders of Neurodevelopment: Autism
• Three core symptoms:
– Reduced ability to interpret emotions
– Reduced capacity for social interaction
– Preoccupation with a single subject or
activity
• Intensive behavioral therapy may improve
function
• Heterogenous – level of brain damage and
dysfunction varies
• Often considered a spectrum disorder
Copyright ©
Pearson Education 2011
Disorders of Neurodevelopment: Autism
• Incidence: 6.6 per 1,000 births (or 1 in 166)
• 80% males, 60% have mental retardation, 35%
epileptic, 25% have little or no language ability
• Most have some abilities preserved – rote memory,
jigsaw puzzles, musical ability, artistic ability
• Autistic Savants – intellectually handicapped
individuals who display specific cognitive or artistic
abilities
– ~1/10 autistic individuals display savant abilities
– Perhaps a consequence of compensatory functional
improvement in one area following damage to
another
Copyright ©
Pearson Education 2011
Genetic Basis of Autism
• Siblings of children with
autism have a 5%
chance of having autism
• 60% concordance rate
for monozygotic twins
• Several genes
interacting with the
environment
Source: Bouchard & McGue, 1981
Copyright ©
Pearson Education 2011
Neural Mechanisms of Autism
Understanding of brain structures involved in
autism is still limited, so far implicated:
• Cerebellum
• Amygdala
• Frontal cortex
Two lines of research on cortical involvement
in autism:
• Abnormal response to faces in autistic
patients
– Spend less time than non-autistic
subjects looking at faces, especially
eyes
– Low fMRI activity in fusiform face area
• Possibly deficient in mirror neuron function
Copyright ©
Pearson Education 2011
Disorders of Neurodevelopment: Williams
Syndrome
• Incidence: 1 in every 7,500 births
• Mental retardation and an uneven pattern of abilities
and disabilities
• Sociable, empathetic, and talkative– exhibit language
skills, music skills, and an enhanced ability to
recognize faces
• Profound impairments in spatial cognition
• Usually have heart disorders associated with a
mutation in a gene on chromosome 7 – the gene (and
others) is absent in 95% of those with Williams
Copyright ©
Pearson Education 2011
Disorders of Neurodevelopment: Williams
Syndrome
• Evidence for a role of
chromosome 7 (as in
autism)
• General thinning of
cortex at juncture of
occipital and parietal
lobes, and at the
orbitofrontal cortex
• “Elfin” appearance –
short, small upturned
noses, oval ears,
broad mouths
FIGURE 9.13 Two areas of reduced cortical volume and one area
of increased cortical volume observed in people with Williams
syndrome. (See Meyer-Lindenberg et al., 2006; Toga & Thompson,
2005.)
Copyright ©
Pearson Education 2011
Watch: The Central Nervous System
Watch: Brain Building
Note: To view the MyPsychLab assets, please make sure you are connected to the
internet and have a browser opened and logged into www.mypsychlab.com.
Copyright ©
Pearson Education 2011
Acknowledgments
Slide
Image Description
Image Source
template
lightning
©istockphoto.com/Soubrette
template
background texture
©istockphoto.com/Hedda Gjerpen
Chapter 09
image
Grandmother and grandchild smelling flowers
©iStockphoto.com/hanhanpeggy
3, 16, 21
28, 30, 33
brain
©istockphoto.com/Stephen Kirklys
4
paper clip
©istockphoto.com/Jon Patton
4
folder
©istockphoto.com/kyoshino
4
tabletop
©istockphoto.com/Andrew Cribb
5
human egg
©istockphoto.com/ChristianAnthony
5
human sperm
©istockphoto.com/Alexander Kozachok
6
Figure 9.1
Pinel 8e, p. 221
7
person thinking
©istockphoto.com/akurtz
9
Figure 9.2
Pinel 8e, p. 222
10
Figure 9.3
Pinel 8e, p. 223
11
book
©istockphoto.com/Carmen Martínez Banús
12
two puzzle pieces
©istockphoto.com/Henrik Jonsson
13
woman observing & taking notes
©istockphoto.com/Claudio Arnese
14
Figure 9.5
Pinel 8e, p.224
15
Figure 9.7
Pinel 8e, p. 227
17
neuron
©istockphoto.com/ktsimage
18
toddler listening to adult speak
©istockphoto.com/Jani Bryson Studios, Inc.
Copyright ©
Pearson Education 2011
Acknowledgments
19
Figure 9.8
Pinel 8e, p. 228
20
two babies
©istockphoto.com/schwester
22
head - woman
©istockphoto.com/Angel Herrero de Frutos
23
hand holding rat
©iStockphoto.com/sidsnapper
24
binoculars
©iStockphoto.com/Alex Staroseltsev
25
Figure 9.10
Pinel 8e, p. 231
26
wires
©istockphoto.com/Take A Pix Media
27
swinging
©istockphoto.com/HooRoo Graphics
28
person with thought bubble
©istockphoto.com/Digital Savant LLC
29
piano and violin
©iStockphoto.com/Yenwen Lu
32
twins
©istockphoto.com/Thomas Gordon
35
Figure 9.13
Pinel 8e, p. 237
36
laptop
©istockphoto.com/CostinT
36
table and wall
©istockphoto.com/David Clark
Copyright ©
Pearson Education 2011