Brain Development, Plasticity and
Relationships to Developmental
Disorders
Behavioral Sciences Lect. 3
Why Brain Plasticity is Important
* Developmental Disabilities (Autism, Learning
Disorders, Mental Retardation): Diagnosis,
understanding, prognosis, treatment
* Normal Development: “Doctor, they say my child needs
special care for the first 3 years. Why? What should I
do?” (Who else are they going to ask?)
* Recovery from brain damage: Alcohol-related
Neurodevelopmental disorder; Closed head injury; Stroke
* Typical and atypical aging (“What about exercise and
the brain?”)
Groups Emphasizing Ages 0 to 3
At ZERO TO THREE, we concentrate exclusively on
these miraculous first years of life - the critical period
when a child undergoes the greatest human growth and
development. It's also a period when you - the parent or
professional - have the opportunity to make a great
impact and positively influence a child's future.
Our mission here is simple: to help children best navigate
their first three years of life in order to develop a solid
intellectual, emotional and social foundation. For parents
and professionals alike, there's always something new
and exciting to be discovered! So, set aside some time to
explore - and come back often and grow with us!
Summary of “Zero to Three” and “I am your Child”
-John Bruer, “The Myth of the First Three Years”
Most simply stated, the argument is this: During the first
three years of life in humans, there is a period of rapid
synapse formation that connects nerve cells into
functioning circuits. This time of rapid synapse formation
is the critical period in brain development. Although the
brain continues to develop after this time, it does so by
losing or eliminating synapses, not by forming new ones.
It is during this critical period when enriched
environments can have the greatest effect on brain
development. Thus the first three years provide…a
unique opportunity, during which the right experiences
and early childhood programs can help children build
better brains.
I Am Your Child (Rob Reiner)
Since its spring launch in 1997, I Am Your Child has
educated millions of parents and professionals about
breakthrough new discoveries in the process of brain
development. These findings reveal that the first three
years of a child's life are more important for emotional
and intellectual growth than previously thought.
Through mass media, community mobilization, public
education and policy outreach, parents and caregivers
across the U.S. and around the world are learning how
to make a difference in the lives of young children.
I am Your Child
“From birth, the brain is rapidly creating these
connections. By the time she is three, your
baby’s brain has formed about 1000 trillion
connections--about twice as many as adults have.
A baby’s brain is super-dense, and will stay that
way throughout the first decade of life.
Beginning at about age eleven, a child’s brain
gets rid of extra connections, gradually making
order out of a thick tangle of "wires." The
circuitry it ends up with is more powerful and
efficient.”
I am Your Child
Q: How does the brain "know" which connections to keep?
A: This is where early experience comes into play. When a
connection is used repeatedly in the early years, it becomes
permanent. In contrast, a connection that is not used at all,
or often enough, is unlikely to survive. For example, a child
who is rarely spoken to or read to in the early years may
have difficulty mastering language skills later on. By the
same token, a child who is rarely played with may have
difficulty with social adjustment as she grows.
Origins of the Critical or Sensitive Period
Concept
Charles R. Stockard
Hans Spemann
Konrad Lorenz
Gilbert Gottlieb
David Hubel & Torsten Wiesel
…it becomes evident that the course of embryonic
development need not progress in a continuous
manner, but may be stopped entirely for a considerable
length of time or may be decidedly reduced in rate
without necessarily injuring the end result. On the
other hand, it is equally well known in a general way,
and even more widely believed, that when a
developing egg is injured in such a manner as to cause
its development to stop, it is usually incapable of
resuming development at all….
-Charles R. Stockard, Am. J. Anat., 1921
As is well-known, a certain organ arises much earlier or
later in the embryo than certain others. When these
primary developmental changes are on the verge of
taking place or when an important organ is entering its
initial stage of rapid proliferation or budding, a serious
interruption of the developmental progress often causes
decided injuries to this particular organ, while only
slight or no ill effects may be suffered by the embryo in
general. Such particularly sensitive periods during
development I have termed the ‘critical moments.’
-Charles R. Stockard, Am. J. Anat., 1921
Spemann & Mangold, 1924
Konrad Lorenz (O.
Heinroth): Imprinting
The Developing Brain Overproduces
Synapses
A Framework for Understanding
Critical Periods and Lifelong
Plasticity: Experience-Expectant and
Experience-Dependent Development
Experience - Expectant Synapse Addition
<- Experience ->
# of Synapses/Neuron
High
Blooming
Blooming
Low
Young
Pruining
Pruning
Relative Age
Old
Critical or Sensitive Periods
• Generally Involve Specific Experiences that
Occur Very Reliably in Development
• “Visual Imprinting” on Mother Bird
• Early Sensory System Development (e.g.,
Vision)
• Some Early Aspects of Language Sound
Recognition
• NOT, in General, Major Aspects of the Cognitive
Development Process
Two Separate Processes Guide Synapse
Formation
• During early development, synapses are
overproduced and experience selects which
survive
• During later development and adulthood,
experience drives the formation of synapses
# of Synapses/Neuron
Experience - Dependent Synapse Addition
High
Experienced
Inexperienced
Low
Young
Relative Age
Old
COMPLEX ENVIRONMENT PARADIGM
Rats Reared in Complex Environments Have More Synapses Per
Nerve Cell
EC=Environmental Complexity; SC=Social Condition; IC=Individual Condition
Synaptic Plasticity in the Brains of Rats
in Complex Environments
• Occurs at any age, at least until very old
• There is no critical period for these effects,
although they are larger in younger animals
• Other brain tissues also change--not just synapses
These Are Not Studies of “Enrichment”
• The rats in these studies are deprived of
stimulation, relative to their natural environment
• No one has studied the brain of an animal given
enrichment above the natural level
• We know little about enrichment and the brain
Blood Vessels
Astrocytes and Oligodendrocytes also hypertrophy
in Complex Environments
Conclusions
• Critical or sensitive periods characterize relatively
basic aspects of sensory and motor development
• There are sensitive periods in development of
some aspects of language perception
• The first 3 years of life are important but not a
critical period after which intervention is
ineffective
• Development is a lifelong process, but the most
important things are most sensitive to input early
Mental Retardation from normal
development gone wrong
The usual cause of Fragile X
Syndrome is expansion of a triplet
(CGG)n repeat in the 5’ untranslated
region of the gene
Dendritic
Dendritic Spine
Spine
Dysgenesis
Dysgenesis in
in Fragile-X
Fragile-X
Syndrome
Syndrome
Hinton et al. Am. J. Med.
Genet., 41: 289-94. 1991.
Dendritic
Spine
Morphology Types
Spine
Characteristics
on
Apical Dendritic Shafts of
Layer V Pyramidal Cells in Human Temporal Cortex
A
B
C
D
Immature
E
F
G
H
Mature
Hypothesis: Fragile X syndrome
involves incomplete dendritic
maturation and pruning
On the horizon: Can we harness the stem cells
of the brain in clinically useful ways?
This is the end of the current set of
slides
Extra Information; Not Required:
What Causes Synapses to Form?
Activity?
Learning?