Module 8 How Does the Nervous System Develop and Adapt? Flashcards
James Heckman
- Argues that investing as early as possible in disadvantaged families promotes optimal development of young children at risk
- Notes that children from Socioeconomic Status (SES) correlate with cognitive development, language, memory, social and emotional processing, and ultimately income and health in adulthood
- Cortical surface area reflects the amount of neural tissue available for different behaviors and correlates positively with cognitive ability
- Should be possible to estimate the effect of early experiences on brain and behavioral development by comparing the cortical surface area and cognitive abilities of people raised in lower-or higher-SES families
- Investigating in children from low-income families will increase societal health and prosperity because these children can optimize their brain development and realize their developmental potential
Kimberly Noble
-Used neuroimaging to investigate the relationship between SES in more than 1000 patients aged 3 to 20
~Lower families income, independent of race or sex, was associated with decreased cortical surface area in widespread regions of frontal, temporal, and parietal lobes
-Measured participant’s cognitive performance on tests of attention, memory, vocabulary, and reading
~Negative effects of low SES were especially dramatic at the lower end of the family income spectrum, especially in families with annual incomes less than 30,000
-Follow-up study showed that lower SES is associated with reduced white matter volume and reduced cognitive flexibility and age-related differences in cortical thickness
Low SES
-Associated with poor nutrition, high stress, and insufficient prenatal and infant care
Neuroscientists to study the relationship between brain and behavioral development from three perspectives
-Structural development can be correlated with emerging behaviors
-Behavioral development can be predicted by the underlying circuitry that must be emerging
-Research can focus on factors such as hormones, injury, or socioeconomic status (SES) that influence both brain structure and behavioral development
~All of these are based on brain development by neurons as they become more and more intricately connected, and increasingly complex interconnections underlie increasingly complex behaviors
Neural structures that develop quickly
-The visual system
~Exhibit their functions sooner than do structures that develop more slowly (speech)
Cognitive behaviors controlled
-By the frontal lobe are among the last to develop
~A skill vital to many complexities of life, including organizing daily activities or making travel plans
tower of Hanoi test
-How planning skills can be measured in the laboratory
-To plan how to move colored discs one by one, in the minimum number of moves, from one configuration to another
~The task is to match the goal in as few moves as possible, obeying two rules
*Only one disc may be moved at a time
*No disc may be placed on top of a smaller disc
-Most 10-year-olds can solve simple configurations, but more difficult versions of the tasks, cannot be performed efficiently until about age 15 to 17
-Adolescents often appear disorganized: their ability to plan has yet to mature
-Mature adults with acquired frontal lobe injuries also fail to perform well on the tower
~Evidence reinforces the idea that children are not miniature adults who simply need to learn the “rules” of adult behavior
-A child’s brain is vastly different from an adult’s, and the brains of children of different ages are not really comparable
Scrutinize behavior for the emergence of new abilities, and then we can infer underlying neural maturation
-As language emerges in a young child, we expect to find corresponding changes in neural structures that control language
-At birth, children do not speak, and even extensive training would not enable them to do so because the neural structures that control language production are not yet ready
~As language emerges, the speech-related structures in the brain are undergoing the necessary maturation
Frontal Lobe structure mature
-Adolescence and into early adulthood, we look fro related changes in behavior
-Can also do the reverse
~Because we observe new abilities emerging in the teenage years and even later, we infer that they must be controlled by late-maturing neural structures and connections
The events that shape how that structure functions and produces behaviors
-Some events that influence brain function are sensory experiences, injuries, the actions of hormones and genes, and SES
If one-factor influences behavior
-Then the brain structure changed by that factor are those responsible for the behavioral outcomes
-We might study how the atypical secretion of a hormone affects both a certain brain structure and a certain behavior
~The presence of testosterone in early development typically occurs at different developmental times in males, or alternatively occurs in females, the structure of the hypothalamus may be altered and consequently, so may sexual preference and perhaps gender identity
Pereformation
-Seneca the Younger (Romon philosopher)
- That a human embryo is an adult in miniature, and thus the task of development is simply to grow bigger
- Was so appealing that it was widely believed for centuries; even with the development of the microscope, the appeal of preformation proved so strong that biologists claimed to see microscopic horses in horse semen
Embryos
- All vertebrate species have a similar-looking primitive head, a region with bumps or folds, and a tail
- Olny as an embryo develops does it acquire the distinctive characteristics of its species
Embryonic Nervous systems over vertebrates
-Similar structurally as their bodies are
-Three-chambered brain of a young vertebrate embryo
~Forebrain
~Midbrain
~Hindbrain
-The remaining neural tube forms the spinal cord
Sperm fertilizes an egg
- The resulting human zygote consists of just a single cell
- This cell soon begins to divide, by day 15 after fertilization, the emerging embryo resembles a fried egg
- Embryonic disc
- Neural plate
Embryonic disc
-A structure formed by several sheets of cells with a raised area in the middle essentially the primitive body
Neural plate
- Primitive neural tissue that gives rise to the neural tube
- Occupies part of the outermost layer of the embryonic cells
- Folds to form the neural groove
Neural tube
- Structure in the early stage of brain development from which the brain and spinal cord develop
- Can be regarded as the nursery for the rest of the CNS
- Open region in the tube’s center remains open and mature into the brain’s ventricles and the spinal canal
Neural stem cell
- Self-renewing multipotential cell that gives rise to any of the different types of neurons and glia in the nervous system
- Lining it has an extensive capacity for self-renewal
- When a stem cell divides, it produces two stem cells; one dies and the other lives to divide again; this process repeats again and again throughout life
Subventricular Zone
-Lining of neural stem cells surrounding the ventricles in adults
Progenitor cells (precursor cells)
-Cell-derived from a stem cell that migrates and produces a neuron or a glial cell
-Neural stem cells have a function beyond self-renewal; they can also divide
-Eventually, produce nondividing cells
~Neuroblast
~Glioblasts
Neuroblast
-Product of a progenitor cell that gives rise to any of the different types of neurons
Glioblats
-Product of a progenitor cell that gives rise to different types of glial cells
Neural stem cells then are multipotent
-They give rise to all the many specialized cell types in the CNS
Sam Weiss
- Discovered that stem cells remain capable of producing neurons and glia not just into early adulthood but even in an aging brain
- Important discovery implies that neurons that die in an adult brain should be replaceable
- Neuroscientists do not yet know how to instruct stem cells to replace them
Gene expression
- Process whereby information from a gene is used in the synthesis of a gene product, such as a protein
- Imaging that certain proteins produce skin cells, whereas other proteins produce neurons
- Similarly, certain proteins produce one type of neuron, such as pyramidal cells, whereas others might produce granule cells
Methylation (DNA methylation)
- Common epigenetic mechanism that suppresses gene expression during development
- A methyl group (CH3) attaches to the nucleotide base cytosine lying next to guanine on the DNA sequence
- Relatively simple to quantify gene methylation in different phenotypes, reflecting either an increase or a decrease in overall gene expression
- Altes gene expression dramatically during development
Prenatal stress
- Can reduce gene methylation by 10%
- Prenatally stressed infants express 2000 more genes (of the more than 20,000 in the human genome) than unstressed infants
Histone modification and mRNA modification
-Can regulate gene expression, but these mechanisms are more difficult to quantify
The chemical environment of a brain cell is different from that of cells elsewhere in the body
- Different genes in brain cells are activated, producing different proteins and different cell types
- Chemical environments needed to trigger cellular differentiation could be produced by the activity of neighboring cells or by chemicals, such as hormones, that are transported in the bloodstream
Neurotropic Factors
-Chemical compound that supports growth and differentiation in developing neurons and may act to keep certain neurons alive in adulthood
Epidermal Growth Factor (EGF)
-When added to the stem cell current stimulates the production of progenitor cells
Blast Growth Factor (bFGF or FGF-2)
-Stimulates progenitor cells to produce neuroblasts
Human brain requires
- Approximately 10 billion cells from just the cortex that blankets a single hemisphere
- It must produce about 250,000 neurons per minute at the peak of prenatal brain development
- This rapid formation of neurons (neurogenesis) and glia (gliogenesis) is just the first step in brain growth; these new cells must travel to the correct destination (migration), they must differentiate into the right type of neuron or glial cell, and the neurons must then grow dendrites and axons and form synapses
- Also prunes unnecessary cells and connections, sculpting itself according to the particular person’s experiences and needs
Hippocampus
-New neurons continue to develop throughout life
Teratogens (Chemicals that cause malformations)
-The fetal brain is especially delicate and extremely vulnerable to injury and trauma
-The developing brain can more easily cope with injury earlier, during neurogenesis, than it can during the later stages of cell migration or cell differentiation, when cells maturation begins
~May be that once neurogenesis has slowed, it is very hard to start it up again
*If neurogenesis is still progressing at a high rate, more neurons can be made to replace injured ones, or perhaps existing neurons can be allocated differently
Absence of neurogenesis in adulthood
-Other than in the hippocampus, also explains why adult brain tumors arise from glial cells, which are generated throughout adulthood, rather than neurons
Brain tumors in young children
-Sometimes neuronal reflecting some lingering neurogenesis
Cell migration
-Begins shortly after the first neurons are generated and continues for about 6 weeks on the cerebral cortex and throughout life in the hippocampus
Cell differentiation
- Which neuroblasts become specific types of neurons, follows migration
- Essentially complete at birth, although neuron maturation, which includes the growth of dendrites, axons, and synapses, goes on for years and in some parts of the brain may continue throughout adulthood
Pasko Rakic
-Subventricular zone contains a primitive cortical map that predisposes cells formed in a certain ventricular region to migrate to a certain cortical location
~One region may produce cells destined to migrate to the visual cortex; another might produce cells designed to migrate to the frontal lobe
Radial Glial Cells
- Path-making cell that a migration neuron follows to its appropriate destination
- Most cortical neurons follow the radial glial cells, a small number appear to migrate by seeking some type of chemical signal
Glial Fibers
- Form each of these path-making cells extends from the subventricular zone to the cortical surface; that neural cell from a given subventricular region need only follow the glial road to end up in the correct location
- As the brain grows, the glial fibers stretch but still go to the same place
Local environmental signals
-Chemical produced by other cells
~Likely influence the way cells form layers in the cortex
-Intercellular signals progressively restrict the choice of traits a cell can express
-The emergence of distinct cell types in the brain result not from the unfolding of a specific genetic program but rather from the interaction of genetic instructions, timing, and signals from other cells in the local environment
Two events take place in dendrite development
- Dendritic arborization (branching)
- The growth of dendritic spines
Dendrites undergo arborization
- In the first 2 years of life
- They develop increasingly complex extensions that look much like leafless tree branches
- Then begin to form spines, where most synapses on dendrites are located
Dendritic growth
-Process at a slow rate, on the order of microns per day
Development of axons
-Grow on the order of a millimeter per day
~About a thousand times faster than dendrites
Disparate developmental rates of axons and dendrites are important
-The faster-growing axon can reach its target cell before the cell’s dendrites are completely formed
-The axon may play a role in dendritic differentiation and ultimately in neuron function
~As part o the brain’s visual, motor, or language circuitry
-Abnormalities in neuronal maturation rate can produce abnormalities in patterns of neural connectivity
~Autism Spectrum Disorder
Autism Spectrum Disorder
- Range of cognitive symptoms from mild to severe that characterize autism; severe symptoms include greatly impaired social interactions, a bizarre and narrow range of interests, marked abnormalities in language and communication, and fixed repetitive movements
- Asperger syndrome
- Rett Syndrome
- Savant Syndrome
- Subcortical amygdala plays an important role in generating fear, and the social withdrawal component of DS may be related to the enlarger amygdala
Asperger Syndrome
- Is distinguished by an obsessive interest in a single topic or object to the exclusion of nearly any other
- Children are socially awkward and also usually have delayed motor skill development
Rett Syndrome
- Characterized by poor expressive language and clumsy hand use
- Almost exclusively affects girls
Savant Syndrome
-A narrow range of exceptional abilities such as in music, art, or mathematics, often accompanied by severe cognitive deficits
Growth Cones
-A growing tip of an axon
Filopod (filopodia)
-Process at the end of a developing axon the reaches out to search for a potential target or to sample the intercellular environment
Growth cones are responsive to cues from two types of molecules
- Cell adhesion molecules (CAMs)
- Tropic molecules
Cell adhesion molecules
-Chemical molecule to which specific cell can adhere, thus aiding in migration
Cell-manufactured molecules that either lie on the target cell’s surface or are selected into the intercellular space
Tropic molecules
- Signaling molecule that attracts or repels growth cones
- To tell growth cones to come over here (chemoattractive)
- Tell other growth cones seeking different targets to keep away (Chemorepulsive
Netrins
-Membre of chemoattractive tropic molecules that guide axon growth
Semaphorins
-Class of chemorepulsive molecules that deflect axons from inappropriate regions
Neural Darwinism
-Hypothesis that the processes of cell death and synaptic pruning are, like natural selection in species, the outcome of competition among neurons fro connections and metabolic resources in natural environment
Apoptosis
-Genetically programmed call death
Dorsolateral prefrontal cortex (DLPFC)
-Brodmann areas 9 and 46: makes reciprocal connections with posterior parietal cortex and superior temporal sulcus; responsible for selecting behavior and movement with respect to temporal memory
Default network
-Brain network of interacting regions of the frontal and parietal lobes that have highly correlated activity
Growth support
-Sporadic period of sudden growth that lasts for a finite time
Chemoaffinity hypothesis
-Proposal that neurons of their axons and dendrites area drawn toward a signaling chemical that indicates the correct pathway
Amblyopia
-Condition in which vision in one eye is reduced as a result of disuse, usually caused by a failure of the two eyes to look in the same direction
Critical period (sensitive period)
-Developmental window during which some event has a long-lasting influence on the brain
Imprinting
-Formation of an attachment by an animal to one or more objects or animals at a critical period in development
Testosterone
-Sex hormone secreted by the testes and responsible for the distinguishing characteristics of the male
Adrogen
-Class of hormones that stimulates or control masculine characteristics
Masculinization
-Process by which exposure to androgens (male sex hormones) alters the brain, rendering it identifiably male
Estrogen
-Variety of sex hormones responsible for the distinguishing characteristics of the female
Psychobiotics
-Treatment that uses live bacteria (probiotics) or compounds to enhance the growth of gut bacteria (perbiotics)
Anencephaly
-Failure of the forebrain to develop
Sudden infant death syndrome (SIDS)
-Unexplained death while asleep of a seemingly heathy infant less than 1 year old
How Does the Nervous system develop and adapt?
- Three perspectives on brain development
- Neurobiology of development
- Correlating behavior with Nervous-system development
- Brain development and the environment
- How does any of us develop a normal brain
Three Perspectives on brain development
- Structural development can be studied and correlated with the emergence of behavior
- Behavioral development can be analyzed and predictions made about what underlying circuitry must be emerging
- Factor that influence both brain structure and behavioral development, such as language or injury, can be studied
Predicting Behavior from brain structure
-Structural development can be studied and correlated with the emergence of behavior
~Brain development (frontal lobe) -> Behavioral development (social development)
-behavioral development can be analyzed and predictions can be made about what underlying circuitry must be emerging
~Behavioral development (Language) -> brain development (brain areas involved in language)
-Factors that influence both brain and behavioral development, such as language or injury, can be studied
~Hormones genes experience injury -> behavioral development or drain development
Neurobiology of development
- Early in development all vertebrates look alike
- Embryonic vertebrate nervous systems
- Forebrain, midbrain, and hindbrain are visible in the human embryo at about 28 days
Gross Development of the human nervous system
-Prenatal stages
-Zygote ~Fertilization to 2 weeks -Embryo ~2 to 8 weeks -Fetus ~9 weeks to birth
Gross Development of the human nervous system
-Neural plate (3 weeks after conception)
-Thickened region of the ectodermal layer that gives rise to the neural tube
Gross Development of the human nervous system
-Neural tube
~Structure in the early stage of brain development from which the brain and spinal cord develop
Neural Tube development in a mouse embryo
- The cells that from the neural tube be thought of as the nursery for the rest of the CNS
- The open region in the center of the tube remains open and matures into the brain’s ventricles and spinal canal
Gross development of the human nervous system
-Major events ~Day 49 *Embryo begins to resemble a miniature person ~Day 60 *Sexual differentiation **Genital's and brain regions ~Day 100 *Brain looks distinctly human ~Month 7 *Gyri and sulci begin to form ~Month 9 *Brain looks like an adult brain
Origins of Neurons and Glia
-Neural Stem Cells
- A self-renewing multipotential cell that gives rise to neurons and glia
- Line the neural tube and have an extensive capacity of self-renewal
- When stem cell divides, it produces two stem cells; one dies and the other lives to divide again
- This process repeats again and again throughout a person’s lifetime
Origins of Neurons and Glia
-Subventriculal Zone
-Lining of neural stem cells surrounding the ventricles in adults
Origins of Neurons and Glia
-Progenitor Cell
- Precursor cell derived from a stem cell; it migrates and produces a neuron or glial cell
- Produce nondividing cells known as neuroblasts and glioblasts
Origins of Neurons and Glia
-Neuroblast
-Product of a progenitor cell that gives rise to different types of neurons
Origins of Neurons and Glia
-Glioblast
-Product of a progenitor cell that gives rise to different types of glial cells
Origins of Neurons and Glia
-How do stem cells know what to becomes? ~Chemical signals to ~Turns genes on (gene expression) to ~Specific proteins are made to ~Specific cells
How do stem cells know what to become?
-Epigenetics
- Methylation alters gene expression dramatically during development
- Chemical environment in the brain is different from skin, so different genes in these cells are activated, producing different proteins and different cell types
How do stem cells know what to become?
-Neurotrophic Factors
-A chemical compound that acts to support growth and differentiation in developing neurons
-May help keep certain neurons alive in adulthood
-Epidermal Growth Factor (EFG)
~Stem cells to progenitor cells
-Basic Fibroblast Growth Factor (bFGF)
~Progenitor cells to neuroblasts
Growth and Development of neurons
-Stages of Brain Development
- Cell Birth (neurogenesis; gliogenesis)
- Cell migration
- Cell differentiation
- Cell Maturation (dendrite and axon growth)
- Synaptogenesis (formation of synapses
- Cell death and synaptic pruning
- Myelogenesis (formation of myelin
Cell Birth (neurogenesis; gliogenesis)
-A chemical compound acts to support growth and differentiation in developing neurons; begins about 7 weeks after conception
-Largely complete by 5 months
-Exception
~Hippocampus makes new cells throughout life
-Brain can more easily cope with injury during this time (first 5 months of gestation)
Cell Migration
- Begins shortly after first neurons are generated
- Continues for 6 weeks in cortex and longer in hippocampus
- Damage has more serious consequences
Cell Migration
-Radial Glial Cells
-Path-making cell that a migration neuron follows to its appropriate destination
Cell Differentation
-Neuroblasts become specific types of neurons
-Begins after cell have begun to migrate
-Essentially complete at birth
~Although neuron maturation, which includes the growth of dendrites, axons, and synapses, goes on for years and, in some parts of the brain, may continue throughout adulthood
Cell Migration and Differentiation
- Ventricular zone contains a primitive map of the cortex that predisposes cells to migrate to certain locations
- Cell migrate to inner layers and then to outer layers (layers6, 5, 4, 3, 2, and 1)
- Differentiation is dependent upon genetic instructions, timing, and signals from other cells in the local environment
Neural Maturation
-After neurons migrate to their final destinations and differentiate into specific neuron types
Neural Maturation
-Mature in two ways
-Dendritic Growth
~Grow dendrites to provide surface area for synapses with other cells
-Axonal Growth
~Extend their axons to appropriate targets to initiate synapse formation
Dendritic growth
- Arborization (branching)
- Growth of dendritic spines where most synapses occur
- Slower (micrometers/day) than axonal growth (millimeters/day)
Axonal Growth
-Growth cone
~Growing tip of an axon
-Filopod
~Process at the end of an developing axon that reaches out to search for a potential target or to sample the intracellular environment
Axonal growth
-Cell-adhesion molecule (CAM)
- On the target’s cell surface or intercellular space
- Provide surface for growth cones to adhere
- Serve to attract or repel growth cones
Axonal growth
-Tropic molecultes
- Produced by targets being sought by the axons
- Tell growth cones to “come over here”
- Likely they tell other growth cones seeking different targets to “keep away”
Synaptic Development
-10^14 synapses in the adult human cerebral cortex
-Combination of genetic programming and environmental cues and signals
-5th gestational month
~Simple synaptic contacts
-7th gestational month
~Synaptic development of deep cortical neurons
-After birth
~Synaptic development increases rapidly during the first year of life
Cell Death and Synaptic pruning
-The brain “chisels” away “pieces” by using cell death and synaptic pruning
~Chisels
*Genetic signal, experience, reproductive hormones, and even stress
-Cortex becomes measurably thinner in a caudal-rostral (back-to-front) gradient, a process that is probably mostly due to synaptic pruning
-We are born with an overabundance of neurons and synaptic connections
-Neural Darwinism
-Apoptosis
-Synaptic connections that are not part of a functional network are pruned away in an experience-dependent manner
Neural Dareinism
-Hypothesis that death and synaptic pruning are, like natural selection in species, the outcome of competition among neurons for connections and metabolic resources in a neural environment
Apoptosis
-Genetically programmed cell death
Gray matter Thickness
- Major language region of the cortex actually show an increase in gray matter
- Color coding represents increasing (blue, white) or decreasing (yellow, green, red) cortical thickness
Unique Aspects of frontal-lobe development
-Frontal lobe is the last brain region to mature
-Maturation extends far beyond age 20
~The frontal lobe is especially sensitive to epigenetic influences
~~The trajectory of frontal lobe development correlates with adult intelligence
Glial Development
- Birth of astrocytes and oligodendrocytes begins after most neurogenesis is complete and continues throughout life
- Oligodendria from myelin in CNS
- Myelination provides a useful rough index of cerebral maturation
Myelination of cortex begins after birth and continues until at least 20 years of age
-Some areas are myelinated earlier (those that preform simple functions) than others (that perform more complex functions)
Correlating Behavior with Nervous-system development
- Behaviors cannot emerge until the requisite neural machinery has developed
- When that machinery is in place, related behaviors develop quickly through stages and are shaped significantly by epigenetic factors
Motor Behaviors
-In infants
-2 months
~Orients hand toward an object and gropes to hold it
-4 months
~Grasps appropriately shaped objects with entire hand
-10 months
~Uses pincer grasp with thumb and index finger opposed
Motor behaviors
- Axon from motor-cortex neurons myelinate about the time that reaching and grasping develop
- Group of motor-cortex neurons known to control finger movements myelinate about the time pincer grasp develops
- Increased motor dexterity is associated with a decrease in cortical thickness in the hand region of the left motor cortex of right-handers
Language Development
-Language onset is usually between 1 and 2
-Language acquisition is largely complete by age 12
-Neural changes during this time
~Increased dendritic complexity and interconnections
~Increase myelination of speech areas
Correlation Between gray-matter thickness and behavior
- Red dots correspond to regions showing significant cortical thinning correlated with improved motor skills
- White dots correspond to regions showing significant cortical thickening correlated with improved language skills
- Red dots show region of decreased cortical thickness correlated with improved vocabulary scores
Development of Problem-solving ability
-Growth Spurts
-Sporadic period of sudden growth that lasts for a finite time
-Epstein
~Identified five spurts in brain growth during development
~First for coincide with onset Piaget’s stages, and the last occur around 14 to 16 years
~Likly due to growth of glial cells, blood vessels, myelin, and synapses
Development of Problem-solving ability
-Overman and colleagues
- Children can learn a concurrent-discrimination task, believed to depend on the basal ganglia, around 12 months
- Children can learn a nonmatching-to-sample task, believed to depend on the temporal lobe, around 18 months
A caution about linking correlation to causation
-Correlation does not equal causation
~Just because the two things correlate (take place together) does not prove that one of them caused the other
Brain development and the environmant
- Brains exposed to different environmental experiences are molded in different ways
- Culture is an important aspect of the human environment, so culture must help to mold the human brain
- People raised in widely different cultures may acquire differences in brain structure that have lifelong effects on their behavior
Experience and Cortical Organization
-Hebb
-Cognitively stimulating environments help maximize intellectual development
-Compared with rats raised in standard lab cages, those raised in “enriched environment” have
~Larger and more synapses
~Larger and more astrocytes
Experience and Neural connectivity
-Prenatally
~Chemoaffinity Hypothesis
-Neurons or their axons and dendrites and drawn toward a signaling chemical that indicated the correct, pathway
Experience and Neural connectivity
-Prenatally
-Fine-tuning of connections proceeds in an activity-dependent manner
Experience and Neural connectivity
-Amblyopia
- A condition in which vision in one eye is reduced as a result of disuse; usually caused by a failure of the two eyes to point in the same direction
- Visual input from the “laze eye” does not contribute to the fine tuning of neural connections
Critical Periods for experience and brain development
-Critical periods
- Developmental “window” during which some event has a long-lasting influence on the brain; often referred to as a sensitive period
- Imprinting
Imprinting
-Process that predisposes an animal to form an attachment to objects or animals at a critical period in development
~Enlargement of synapses in chick forebrain
Abnormal Experience and brain development
-Early deprivation of sensory experience
_Being placed in the dark has the opposite effect of cognitively stimulating environments
~Atrophy of dendrites
Abnormal Experience and brain development
-Early deprivation of social experience
-Raised without maternal contact has a profoundly negative effect on later intellectual and social behaviors
Abnormal Experience and brain development
-Human cases
-If deprivation is relatively short (less than a few month), the child may not be able to overcome some of the negative effect
Abnormal Experience and brain development
-Stress in early life have been associated with
- Amygdala increases in size
- Hippocampus decreases in size
- Later development of depression and anxiety disorder
Hormones and brain development
-Testosterone (Androgen)
-Released during a brief period in the course of prenatal brain development and subsequently acts to alter the brain much as it alters the sex organs
Hormones and brain development
-Estrogen
0Sex hormones responsible for the distinguishing characteristics of the female
Hormones and brain development
-The presence of testosterone and estrogen both affect the development of the brain
-Number of neurons formed
-Number of neurons that die
-Cell growth
-Dendritic branching
-Synaptic growth
-Activity of synapses
~Not just the areas of brain related to sexual behavior
*These hormones can affect “higher functions” such as cognition
Hormones and brain development
-Bachevalier and colleagues: Postnatal effects
~Monkeys
- Male and females showed different patterns of performance on tests at 2.5 months old
- Males that had testes removed at birth preformed more like females
Hormones and brain development
-Bachevalier and colleagues: Postnatal effects
~Humans
- Similarly, males and females showed different patterns of performance around 15 to 30 months of age
- Sex differences disappeared at 32 to 55 months of age
Hormones and brain development
-Juraska: postnatal effects
~Rats reared in complex environments
-Males showed more dendritic growth in the visual cortex than females
-Females showed more dendritic growth in frontal lobes than males
-Summary
~Sex differences in brain structure exist throughout development
Injury and brain development
-Humans
-Worst time for brain injury
~Last half of intrauterine period and the first few months after birth
-“Better” time for brain injury
~First few years after birth
~More resilient to deficits (language impairments) than when damage occurs in adults
Drugs and Brian development
-Precise effects of drugs on prenatal brain development are poorly understood
-There is some evidence that
~Prenatal exposure to psychoactive drugs may increase the chance of later drug use
~Prenatal exposure to drugs such as nicotine and caffeine increase the chance of learning disabilities and hyperactivity
Other kings of abnormal brain development
-Genetic abnormalities
~Spina bifida
- Spinal cord abnormality due to the failure of the neural tube to close completely
- Associated with serous motor problems
Other kings of abnormal brain development
-Genetic abnormalities
~Anencephaly
- Front end of the neural tube does not close
- Failure of the forebrain to develop
- Infants typically die soon after birth
Other kings of abnormal brain development
-Abnormal Cell Migration and Differenctation
-Faulty connections may produce a range of problems
~Schizophrenia
*Disorganized pyramidal neurons i the hippocampus
-Too many synapses (failure of pruning) can also produce neural dysfunction
Other kings of abnormal brain development
-Behavioral effects of brain damage to a certain area are often not seen until the time at which that particular area matures
~The frontal lobes continue to develop into adulthood, therefore, the behavioral effects of frontal lobe damage may not be seen until adolescence
Developmental Disability
-Impaired cognitive functioning due to abnormal brain development
-Many causes
~Genetic abnormalities (down syndrome)
~Prenatal exposure to infections (rubella) or toxins such as alcohol (fetal alcohol syndrome)
~Birth trauma, such as anoxia (cerebral palsy)
~Malnutrition
~Environmental abnormality, such as sensory deprivation (Romanian orphans)
Developmental Disability
-Purpura
- Examined children with developmental disabilities who died from accidents or diseases unrelated to the nervous system
- Compared with normal children, dendritic growth was reduced in children with various forms of mental retardation
- Suggests that there were fewer connections in the brain
How do any of us develop a normal brain
-Brain has a substantial capacity to repair minor abnormalities that may occur during development (plasticity)
-There is a “range of normality” with respect to brain development
~Most of us develop a brain that falls within a certain range of normality
-Plasticity occurs into older adulthood
