Early Brain Development

brains are built over time, shaped by the interaction between

genetics and experience

social, emotional, and cognitive development are

highly interrelated

brain architecture and skills are built in a

hierarchical “bottom-up” sequence

brain plasticity and the ability to change behavior ________ over time

decrease

what contributes to psychobiological development?

brain development, developmental behavioral and molecular genetics, nutrition

what contributes to psychobehavioral development?

cognition, emotions, language, memory, attachment

the foundation of a successful society is built in

early childhood

how does healthy child development contribute to a successful society?

leads to educational achievement, economic productivity, responsible citizenship, lifelong health, successful parenting of next generation, strong communities, and healthy economy

three core concepts of development

1. brain architecture is established early in life and supports lifelong learning, behavior, and health

2. stable, caring relationships and “serve and return” interaction shape brain architecture

3. toxic stress in the early years of life can derail healthy development

time range from CNS development

3 weeks to 20 years

early beginnings of growth and differentiation of the vertebrate brain

CNS begins to form at 3 weeks gestation

development of the neural tube

at birth, brain weighs 350g, at one year 1000g

neuron proliferation

production of new cells

neuron migration

move toward final destination

neuron differentiation

form axons and dendrities

neuron myelination

addition of insulating sheath

prenatal stage of development

conception to birth

characterized by rapid physical growth

infancy stage of development

birth to 2 years

characterized by motor development

childhood stage of development

2-12 years

characterized by abstract reasoning

adolescence stage of development

13 to 25 years

characterized by identity creation, judgement (which is directly related to maturation of the prefrontal cortex)

piaget’s object permanence test

an infant sees a toy and then an investigator places a barrier in front of the toy

infants younger than about 9 months old fail to reach for the hidden toy

tasks that require a response to a stimulus that is no longer present depend on the

prefrontal cortex, a structure that is slow to mature

zygote

formed from the ovum and sperm

embryo

composed of germinal layers of cells from which the various organs later derive

forms once zygote implants in uterus

fetus

from week 8 until birth

cell creation and movement to the correct places occurs

during the first dive prenatal months

5 phases of brain development

1. neural plate induction

2. neural proliferation

3. migration and aggregation

4. axon growth and synapse formation

5. cell death and synapse rearrangement

embryonic stage of development

includes the process of organogenesis, transformation from the embryo to a body structure including defined organs

during the third week, the development of the ________ provides an axis upon which other structures can organize

primitive streak

neurulation

process in embryos, generates a dorsal rod shaped structure termed a notochord which serves as a primitive skeleton, later replaced by the vertebral column

notochord

generated from the primitive streak during neurulation, serves as a primitive skeleton

ectoderm

layer from which the nervous system develops, located above the notochord

neural tube

nervous system development proceeds from the generation of the neural plate to neural folds, which eventually develop into this

what happens 18 days after conception?

the embryo begins to implant in the uterine wall

a patch of tissue on the dorsal surface of the embryo that will become the nervous system

consists of 3 germinal layers of cells: endoderm, mesoderm, and ectoderm

thickening of the ectoderm layer leads to the development of the neural plate

what happens at 20 days after conception?

the neural groove begins to develop

what happens at 22 days post-conception?

the neural groove closes along the length of the embryo making the neural tube

what happens at 24 days post-conception?

brain subdivides into the forebrain, midbrain, hindbrain

components of forebrain at 24 days post-conception

telencephalon, diencephalon

components of midbrain at 24 days post-conception

mesencephalon

components of hindbrain at 24 days post conception

rhombencephalon

neuroepithelial cells

the stem cells of the nervous system

those of the ectoderm proliferate leading to generation of new cells

3 swellings at the anterior end in humans will become the forebrain, midbrain, and hindbrain

neural mitosis and proliferation

occurs in the ventricular zone

rate can be 250,000/min

daughter cells become fixed post-mitosis

migrating neurons structure

immature, lacking dendrites, with only a soma and immature axon at this point

undifferentiated at the start

differentiation begins as this process starts- develop neurotransmitter making ability, action potential

neuroepithelial cells of the ventricular zone

give rise to radial glial cells that further differentiate into neurons or glial cells (e.g. astrocytes)

radial glial cells

act as guide wires for the migration of neurons

neural aggregation

cells that are done migrating align themselves with other cells and form structures

the forebrain, midbrain, and hindbrain further divide,

each with a fluid filled region: ventricle, aqueduct, or canal (spinal cord also has a canal)

two major bends, or flexures, occur

what are the two major bends/flexures that occur during embryonic development?

midbrain and cervical

telencephalon

forms cerebrum (cerebral hemispheres—cortex, white matter, basal nuclei) and lateral ventricles

diencephalon

forms diencephalon (thalamus, hypothalamus, epithalamus) and third ventricle

mesencephalon

forms midbrain (brain stem) and cerebral aqueduct

metencephalon

forms pons (brain stem), cerebellum, and fourth ventricle

myelencephalon

forms medulla oblongata (brain stem) and fourth ventricle

spinal cord

forms central canal

gyri

elevated ridges, entire surface

grooves separate them

sulcus

a shallow groove

separate gyri

fissures

deeper grooves

separate gyri

space restrictions force cerebral hemispheres

to grow posteriorly over rest of brain, enveloping it

grow into horseshoe shape, continued growth causes creases, folds, wrinkles

gray matter

neuronal cell bodies (brown when fixed), dendrites, and axon terminals of neurons

it is where all synapses are

white matter

neuronal axons coated with electrical insulation called myelin, connecting different parts of grey matter to each other

once aggregation has occured,

axons and dendrites begin to grow to their mature size and shape

axons and dendrites

form a synapse with other neurons or tissue (e.g. muscle)

growth cones and chemo-attractants are critical for this (e.g. NGF)

synaptogenesis

formation of new synapses

most occurs through the 2nd year of life

although most neurons are formed halfway through gestation there are virtually no synaptic connections, it is

experience and interaction with the environment that forms the synaptic connections

_____ of dendritic growth (connections between synapses) occurs after birth

83%

synaptic cleft

space between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter

dendrites

receive messages from other cells

axon terminal

passes on message to other cells

although most of the brain material and size is in place at the start of adolescence,

several important developmental processes continue like myelination and synaptic refinement/rearrangement

after birth development

refinement of neuronal connections, maturity of the neurons, and increasing complexity of dendrite interconnections

_______ neurons made will die after migration—death is normal and necessary!

40-75%

why do neurons die?

due to failure to compete for chemicals provided by targets

neurotrophins

a family of proteins (e.g. NGF, BDNF)

promote growth and survival, guide axons, stimulate synaptogenesis

apoptosis

a preprogrammed mechanism of cell death

axons not exposed to neurotropins after making connections undergo this

therefore, the health adult nervous system contains no neurons that failed to make appropriate connections

natural selection of brain wiring (neural darwinism)

neurons and synapses must get hooked together properly to develop specific skills and abilities in humans

how the right connections are made is still being researched

during infancy and early childhood the developing cortex overproduces synapses (2x as needed)

overproduction leads to a competition for survival of the fittest synapses (competition for neurotrophin, nerve growth factor)

after maturity, the apoptotic mechanisms become dormant

neurons no longer need neurotrophins for survival, but neurotrophins increase the branching on axons and dendrites throughout life

up to _______ synapses are pruned per second

100,000

synaptic production and pruning correspond with

overall brain activity

young children’s brains work harder and less efficiently than adults

experience-expectant synapse development

overproduce synapses, prune with experience

experience leads to less

tied to critical/sensitive periods

organizes brain to process information, behaviors expected for all humans (sensory processes, parental attachment, eye-hand coordination, language capacity)

experience-dependent synapse development

new synapses formed, maybe some pruning

experience leads to more

continues throughout life

codes experiences/learning that is person-specific (a particular language, specific knowledge, memories, skills)

infant rats and synaptic pruning

enrichment reduced synapse density

facilitated pruning of excess synapses in experience-expectant development

prune > gain

adult rats and synapse pruning

enrichment increased synapse density

facilitated growth of new synapses in experience-dependent development

gain > prune

experience influences both pruning and growth of new synapses in an

age development manner

active synapses

receive enough neurotrophic factor to remain stable

inactive synapses

receive too little neurotrophic factor to remain stable

myelination

process whereby glial cells (formed by oligodendrocytes in the CNS and Schwann cells in PNS) wrap themselves around axons

increase speed of action potential conduction down the axon

begins at birth, rapidly increases to 2 years old

continues to increase more slowly through 30 year olds

electrical insulation

dendritic growth and synapse refinement are coated in myelin, which serves as this

when electrical impulses travel from neuron to neuron, some of their strength can be lost or leaked or can collide and interfere with other impulses, myelination speeds up the travel of the impulses and makes their travel more efficient

myelin composition

15% cholesterol with 20% protein which is why doctors recommend breast milk for babies—this content and speeds of electrical signals rise with breastfeeding

8 phases in embryonic and fetal development at cellular level

1. mitosis/proliferation

2. migration

3. differentiation

4. aggregation

5. synaptogenesis

6. neuron death

7. synapse rearrangement

8. myelination

postnatal growth

a consequence of synaptogenesis, increased dendritic branches, myelination (prefrontal cortex continues into adolescence)

plasticity

overproduction of synapses may underlie this

young brain more able to recover function after injury, as compared to older brain

cerebrum (cerebral cortex)

brain has left and right hemispheres covered by this, a layer of nerve tissue

each half has 4 different lobes

structures underneath the cerebrum

amygdala, thalamus, corpus callosum, hippocampus, all of which play important roles in human behavior, memory, emotions

fully developed forebrain parts

cerebrum (cortex), thalamus, hypothalamus (part of the limbic system)

fully development midbrain parts

tectum and tegmentum

fully developed hindbrain parts

cerebellum, pons, medulla

brainstem

midbrain, pons, medulla are referred to together as this

basic functions including heart rate, breathing, sleeping, eating

frontal lobe

self-regulation, problem solving, goal setting, social cognition

frontal association area, speech, motor cortex

judgement, emotional regulation, problem solving, decisions, planning, creativity, executive functions

occipital lobe

vision and perception, visual association area

processes visual input that is sent to the brain from the retinas

parietal lobe

sensory motor perception, spatial abilities, somatosensory cortex, taste, speech, somatosensory association area, reading

major sensory inputs from the skin (touch, temperature, pain receptors) relay through the thalamus to here

temporal lobe

hearing, language, memory, social-emotional function, emotion, smell, auditory association area

combines auditory and visual information, as well as recognition depending on memory (i.e. faces, music)

limbic system

emotion

made of limbic cortex, septal area, thalamus, hippocampus (memory), amygdala (emotions like fear/anxiety), hypothalamus (limbic output)