ch 23 - Brain Development and Plasticity

what are the three main approaches to studying brain development?

• looking at the maturation of different brain structures and correlate that development with the emergence of specific behaviors

• observe behaviors that emerge and make predictions about the neural changes that would support that behavior

• identify factors that influence the development of both the brain and behavior

when does the neural plate fold into the neural tube?

21-25 days gestation

rolled up sheet of cells that will form the brain and spinal cord

neural tube

after the neural tube forms, what structures begin to develop?

forebrain, midbrain, and hind brain

what is the major developmental point at 100 days (14ish weeks)

the brain has normal shape (no gyri/sulcu)

sulci and gyri start to develop at ___. full gyrification is present at ___

sulci and gyri start at 7 months gestation, gyrification present at 9 months gestation

what is different about a brain at 9mos gestation and an adult brain?

cellular structure (but gyrification is the same)

what are the two principal features of brain development?

cell destination and function are predetermined

development moves from overabundance to pruned efficiency via apoptosis

when does neurogenesis (and cell migration) occur? synaptogenesis?

neurogenesis and cell migration are largely complete by birth. synaptogenesis begins before birth and continues (along with neuronal maturation and myelination) for the first several months after birth

how do the different brain regions differ developmentally?

developmental changes take place at different rates in different brain regions

what major brain region is the first to develop and finish pruning?

sensorimotor cortex

what major brain region is the last to finish developing and finish pruning?

prefrontal cortex

list the stages of brain development

cell birth (neurogenesis + gliogenesis)

cell migration

cell differentiation

cell maturation

synaptogenesis

cell death and synaptic pruning

myelogenesis

in which developmental stage does dendrite and axon growth occur?

in the cell maturation (4th) stage

where do neural stem cells grow out of?

neural tube

what are progenitor cells? what are they produced from and what do they produce?

progenitor cells are precursor cells. they are produced from neural stem cells. progenitor cells produce neuroblasts and glioblasts that mature into neurons and glial cells.

do neuroblasts and glioblasts divide?

no

what lines the subventricular zone in adults?

stem cells

where does neurogenesis occur in adulthood?

olfactory bulb/caudate and in hippocampus.

describe the first stage of neurodevelopment.

1: neurogenesis

neural stem cells grow out of the neural tube and produce progenitor cells that mature into neurons and glia

during cell migration, cells migrate along ___ from the ___ to the ___

cells migrate along radial glial fibers from the subventricular zone to the surface of the brain

cortex is built from

• inside out

• outside in

inside out

___ has “map” of cortex and ___ are like roads headed there

ventricular zone is map, radial glia are roads

cortex is formed by ___ but cell migration continues to about ___

cortex formed by 4.5 months gestation, but cell migration continues to about 8 months after birth

brain has an increased sensitivity to trauma in what phases of neurodevelopment?

stages 2/3: cell migration and differentiation

disturbances to cell migration usually leads to

seizures, dyslexia, other neurodevelopmental disorders

what animal is used in research for a model of when cortex is built outside in?

reeler mouse

describe the second and third stages of neurodevelopment.

2/3: cell migration and differentiation

cells migrate along radial glial fibers from the subventricular zone to the surface of the brain, building the cortex from inside out. neurons differentiate and migrate to the associated location (ex. visual cortex neuron → occipital lobe)

what are the steps of neural maturation?

1. dendritic development

2. axonal development

how is cell maturation determined by the dendrites (think about a neuron stain)

during the maturation process, neurons develop more dendritic arborization and dendritic spines

compare and contrast dendritic growth and axonal growth

dendritic: slow process

axonal: faster process

what is the purpose of dendritic arborization and developing dendritic spines?

increase surface area for synapses with other cells

why is is important that axons grow faster than dendrites?

axons have a further distance to go. it allows dendrite and axon to reach synapse at same time

failure of the axon to reach appropriate target results in

death of the neuron (the whole neuron, not just axon)

axonal growth can be disrupted by

blocked path (like from scar tissue), abnormal development, damage to axon’s target

athetosis

slow involuntary movements. can result from incorrect pathway formation during the axonal growth stage.

dystonia

imbalances in muscle tone. can result from incorrect pathway formation during the axonal growth stage.

as a way for axons to overcome obstacles to reach their targets: if spinal cord is damaged, ___ axons can cross to undamaged side and recross

pyramidal tract

describe stage 4 of neural development

4: neural maturation

cells have migrated and are in place. now they develop their dendrites (slow process), then their axons (fast process). the dendrites and axons mature at their separate paces in order to meet their targets at the same time.

___ guide the formation of synapses (3 things)

genes, cues, and signals

what are the five phases of synapse formation?

1 and 2: synapses generated independently of experience (in utero)

3: rapid growth from birth to age 2

4: plateau and rapid elimination through puberty

5: another plateau in middle age, then steady decline with older age (experience dependent)

___% of synapses lost through puberty

50%

experience expectant synapses

development depends on the presence of sensory experiences (phases 3 and 4 /birth-puberty)

experience dependent synapses

generation of synapses that are unique to the individual (phases 3, 4, 5/everything post birth)

experience expectant and experience dependent are both types of

plasticity

experience-(expectant/dependent): visual cortex synapses depend on exposure to features such as line orientation, color, movement

expectant

experience-(expectant/dependent): Visual system synapses correspond to learning of specific visual info (ie., facial features)

dependent

dendritic spine loss (pruning) continues in the ___ until the 30s

PFC pyramidal neurons

___ areas lose synapses before PFC does

primary sensory

spine density on pyramidal neurons in the DL PFC peaks around age ___

5

describe stages 5 and 6 of neural development

5/6: synapse formation and pruning

synapses form in utero and after birth (until puberty), then pruning of synapses occurs throughout the lifespan. formation and pruning occurs at different rates for different areas of the brain.

when does glial development begin and end?

it begins after neuronal development and continues throughout life

when does myelination begin and end?

myelination begins after birth and continues into adulthood.

rough marker of cerebral maturation

myelination

what cortical area is myelinated first? which is last?

sensory areas first, association cortex last

which scientist produced a map that shows the progress of myelination?

Fechsig

areas early to myelinate control ___. areas later to myelinate control ___.

early - simple movement or sensory analyses

late - higher mental functions

describe stage 7 of neurodevelopment

7: myelogenesis

astrocytes and oligodendrocytes form, and myelination begins (after birth). myelination occurs throughout life, with areas associated with higher mental functions finishing last.

anencephaly

cerebral hemispheres, diencephalon, and midbrain are absent

holoprosencephaly

cortex forms as a single undifferentiated hemisphere

lissencephaly

brain fails to form sulci and gyri and corresponds to that of a 12 week embryo

micropolygyria

gyri are more numerus, smaller, and more poorly developed than typical

macrogyria

gyri are broader and less numerous than typical

microencephaly

development of the brain is rudimentary and the person has low intelligence

porencephaly

cortex has symmetrical cavities where the cortex and white matter should be

heterotopia

displaced islands of gray matter appear in the ventricular walls or white matter, caused by aborted cell migration

callosal agenesis

entire corpus callosum or a part of it is absent

cerebellar agenesis

parts of the cerebellum, basal ganglia, or spinal cord are absent or malformed.

adolescence is characterized by 

rapid pruning and rapid growth of new connections

gray matter loss is from ___, white matter gain is from ___

neuron and synapse pruning, myelination

spatial and language regions mature at ___

puberty (11-13y)

physical and hormonal changes are related to 

patterns of brain maturation

vocabulary scores correlate (negatively/positively) with thickness of the cortex during development

negatively

(more cortical thinning = better vocab development)

vocab findings are more ___ in left hemi and ___ in right hemi

more widespread in left, focal in right

how does prefrontal-subcortical circuitry change throughout the lifespan?

overall, the connections between prefrontal and subcortical areas become stronger.

go from more subcortical-subcortical connections to cortico-subcortical circuits

studies of white matter connectivity showed that ___ fibers develop before ___

interhemispheric before intrahemispheric

children with ADHD have a reduced volume of ___ matter in the ___

gray matter in PFC

sometimes, kids with ADHD have a decrease in PFC gray matter volume that is not permanent, but instead represented ___

a delay of about 2.5 years for the development of gray matter compared with non-ADHD controls

The brain regions associated with response inhibition were significantly larger in ___ than ___

larger in children than adults

brain growth spurt periods line up fairly well with ___

Piaget’s stages of cognitive development

theres a ___% increase in brain weight in each growth spurt

5-10%

Both human and monkey infants learn the discrimination task earlier than the non-match to sample task. this suggests…

brain regions that support the easier task must develop sooner than those that support the harder task

in utero environmental effects on brain development

mother’s exposure to stress, prescription drugs, recreational drugs, caffeine

microbiome

epigenetics

lead poisoning

SES

Kennard Principle

Functions are spared when injury occurs during infancy, the earlier the better for regaining function (more plastic)

how was the Kennard principle modified by Hebb?

found that injury too early is also bad

what age has the best prognosis for brain injury?

1-5 years