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 3At 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. StockardHans SpemannKonrad LorenzGilbert GottliebDavid 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

Relative AgeYoung Old

High

Low

# o

f Syn

apse

s/N

euro

n

Blooming PruiningBlooming Pruning

<- Experience ->

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

Experience - Dependent Synapse Addition

Relative Age

Young Old

Experienced

InexperiencedHigh

Low

# of Synapses/Neuron

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 Spine Dysgenesis in Fragile-X

Syndrome

Dendritic Spine Dysgenesis in Fragile-X

Syndrome

Hinton et al. Am. J. Med. Genet., 41: 289-94. 1991.

Spine Characteristics on Apical Dendritic Shafts of Layer V Pyramidal Cells in Human Temporal Cortex

A B C D E F G H

Dendritic Spine Morphology Types

MatureImmature

Hypothesis: Fragile X syndrome involves incomplete dendritic maturation and pruning

On the horizon: Can we harness the stem cellsof 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?