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Brain Development, Plasticity and Relationships to Developmental
Disorders Why Brain Plasticity is Important
* Developmental Disabilities (Autism, Learning Disorders, Epilepsy,
Mental Retardation): Diagnosis, understanding, prognosis, treatment
* Normal Development: Doctor, they say children need special
attention for the first 3 years.Why? What should I do?(Who else are
they going to ask?) * Recovery from brain damage: Fetal
AlcoholSyndrome; Alcohol-related neurodevelopmental disorder;
Cerebral palsy; Perinatal hypoxia, Closed head injury; Stroke *
Typical and atypical aging (What about exercise and the brain?) I
am Your Child From birth, the brain is rapidly creating
connections. By the time she is three, your babys brain has formed
about 1000 trillion connections--about twice as many as adults
have. A babys brain is super-dense, and will stay that way
throughout the first decade of life. Beginning at about age eleven,
a childs brain gets rid of extra connections, gradually making
order out of a thick tangle of "wires." The circuitry it ends up
with is morepowerful and efficient. I am Your Child Q: How does the
brain "know" which connections to keep
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
Origins of the Critical or Sensitive Period ConceptCharles 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 The Critical Period concept arose from
embryology: 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
Critical/Sensitive Periods and the BrainThe Developing Brain
Overproduces Synapses How do we resolve synapse loss with brain
functional improvement
How do we resolve synapse loss with brain functional improvement?A
Framework for Understanding Critical Periods and Lifelong
Plasticity: Experience-Expectant and Experience-Dependent
Development Experience - Expectant Synapse Addition
High # of Synapses/Neuron Blooming Blooming Pruning Pruining Low
Young Old Relative Age Blakemore, Hubel & Wiesel Experienced
Eye Columns
Deprived Eye Columns Visual Cortex Simple Cell Vertical Horizontal
Visual Development Process
What drives early synapse stabilization and loss is neural activity
in optic nerve, driving lateral geniculate nucleus and cerebral
cortex development. Early in development, this activity is
generated by the retina, even in the absence of visual experience,
beginning the process. Vision takes over later. Other features such
as myelin (enhances axonal conduction) are also activity dependent
(e.g., eye closure reduces myelination of axons in optic nerve).
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 Apparently some aspects of early social development
NOT, in General, Major Aspects of the Cognitive Development Process
Normal Social Development Requires Social Experience
Isolation of macaque monkeys during development impaired later
social interactions, mating, and parenting (Harlow) Rehabilitation
(social exposure to young monkeys) is possible; earlier is better
(Suomi) Maternal deprivation early (removal of mother from the
troop) affects social development even though infant adopted by
adolescent or adult females in group (Cameron) These effects of
experience upon behavioral development appear to involve changes in
the brain--as with sensory system development 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 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: Delaying experience can be detrimental Other brain tissues
also change--not just synapses These Are Probably 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 NORMAL DEVELOPMENT is important 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 single
critical period after which intervention is ineffective Development
is a lifelong process, but the most important things are most
sensitive to input early Fetal Alcohol Syndrome Applying knowledge
of development
Example of Prenatal Sensitive Period and of Physicians Behavioral
Intervention Applying knowledge of development Characteristic
Facial Features of Child with FAS
Short Eyelid Opening,Flat Midface,Short Nose,Indistinct Philtrum
(depression beneath the nose),Thin Upper Lip,Epicanthal Folds,Low
Nasal Bridge,Minor Ear Abnormalities,Short Chin Corpus callosum
agenesis in FAS patients
Control Thin c.callosum Absent c.callosum (From Mattson et al.,
1994) Loss of Purkinje cells in PML of rat exposed to alcohol
postnatally IQ distribution for FAS and FAE compared
with the normal curve (From Streissguth et al., 1996) Prevalence of
Secondary Disabilities across the Life Span History of Mental
Health Problems (MHP) by sex, diagnosis and age at interview
(n=415) How Much is Too Much? Outcome of maternal drinking during
pregnancy depends on: stage(s) of fetus development when drinking
occurred peak BAC reached during drinking episode(s) mothers
individual situation (health and build, nutritional status, level
of alcohol dehydrogenase) Change in Drinking by pregnant
women
after contact with Seattle Pregnancy and Health Program (From
Little et al., 1984) By asking if 1) the individual ever consumes
five or more drinks on any occasion, and 2) if she ever feels that
she should cut down on drinking, clinicians could detect 92% of the
women identified as being at genuine risk by the intervention
interview. --Streissguth, 1997 Pregnancy and Health Program
Intervention Procedure
Provide Information on Alcohol and Pregnancy Recommend Abstaining
from Alcohol during the remainder of the pregnancy Help Each Woman
Work Out an Individual Plan of Action --Streissguth, 1997
Developing an Action Plan with the Pregnant Patient
Do you need help with your drinking In what sorts of situations are
you likely to drink? I dont want you to drink.It matters to me.
Your child matters to me. When is it hardest for you not to drink?
NEVER: One drink a day probably wont hurt. This is not reinstating
prohibition.There are legitimate, scientifically-based reasons not
to drink when pregnant. Developing an Action Plan with the Pregnant
Patient
Assuming a clear, credible decision is made not to drink: The only
clear limit for number of drinks per day is none. If the patient
resists eliminating alcohol consumption entirely: How much can you
cut down by the next time you see me What can you do to reduce your
drinking? The goal is to minimize drinking if it cannot be
eliminated and to avoid multiple drink situations likely to yield
high peak blood alcohol levels.Try to work with pt to restructure
behaviors, e.g.. not going out with friends on Friday night after
work. What if the patient wont stop drinking?
Alcohol treatment center referral (e.g., Prarie Center, New Choice,
Mental Health) If beyond the point of probable serious damage,
There is a set of options.I cannot recommend any particular one,
but I can discuss them all with you.Here is where your child may
stand. (In this context, pregnancy termination is an option.)
Mechanisms of memory in adults
Long-term potentiation: increased synaptic strength following high
frequency activation, thought to involve increases in glutamate
receptors (AMPA) available at the membrane. Long-term depression:
selective weakening of synaptic strength due to neurotransmitter
and/or glutamate (AMPA) receptor differences.
Alpha-amino-3-hydroxy-5methyl-4-isoxazole propionate (AMPA)
receptors are activated by glutamate Mechanisms of memory in
adults
Synapse formation: New synapses are induced in many brain regions
following learning appropriate to those regions (e.g., hippocampus
for spatial or declarative tasks; cerebellum for procedural or
motor skill tasks). Synaptic efficacy modification: selective
strengthening or weakening of synaptic efficacy due to
neurotransmitter and/or receptor differences. Brain plasticity in
adults
Neurogenesis: Some brain regions such as the hippocampal dentate
gyrus are capable of generating new neurons (and other cell types)
throughout most of life. For most regions neurogenesis is very
limited in adulthood. Gliogenesis: The formation of new astrocytes
and oligodendrocytes occurs to at least a limited degree in many
brain regions and may be increased by neural activity. This may
play a role in recovery from brain damage. Brain aging in adults
With aging, brain weight may decline, ventricles and sulci may
become enlarged and blood flow may decline. There is evidence that
these changes are mitigated by physical and mental activity.
Pathological aging, as in Dementia of the Alzheimers type, involves
excess pathology such as senile plaques and neurofibrillary
tangles. Brain aging in adults Parkinsons Syndrome, a movement
disorder involving ataxia (impaired initiation and control of
movement) and tremor, is associated with loss of brainstem
noradrenergic neurons. Evidence is increasing that the proposed use
it or lose it recommendation applies both to healthy and to
pathological aspects of aging.