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.