Neural Development and Brain Assembly

Neural Development

• Adult cortex contains 14-16 billion neurons.
• There are 61 billion glial cells, which provide support.
• Glial cells moderate neuron firing and are implicated in Alzheimer's and other conditions.
• Neurons vary significantly in shape, form, and interconnections.
• Diversity in cell types includes basket cells, chandelier cells, and Martinotti cells.
• The goal of studying neural development is to understand how diversity is achieved, how cells organize into specific areas, and how the CNS integrates for coherent function.
• Brain divisions and subdivisions have unique structures and functions, visible through imaging.

Assembly of the Brain

• The genome serves as the genetic blueprint for the brain.
• Neurons and glial cells are the building blocks of the nervous system.
• Neurons, the basic units, consist of a cell body with a nucleus, dendrites (receiving chemical signals), and an axon (transmitting electrical signals).
• Axon terminals pass information via chemical messages (neurotransmitters) to other neurons.
• Myelin sheaths insulate the axon, increasing the speed of electrical signals.
• Glia are non-neuronal cells that support neuron function through gliogenesis.
• Axons, dendrites, and synaptic connections form the wiring for electrical and telephone-like communication.
• Most postnatal brain growth occurs within 3-4 years.
• Myelination continues into old age (70-80 years), with glial cells wrapping axons for faster transmission.
• Hippocampus (long-term memories), synapses, and axons continue to grow throughout life.

Neurulation

• Neurulation (week 3-4 of pregnancy) is the differentiation of the neural tube.
• The neural crest breaks off and the neural tube folds.
• The bottom 50% of the neural tube becomes the spinal cord.
• The middle part becomes the brain stem.
• The top part becomes the brain.
• Encephalization is the disproportionate growth of the top part of the tube.
• The tube differentiates into three vesicles.
• Developmental subdivisions precede functional subdivisions.
• Neurulation occurs in the embryo, while brain area differentiation occurs in the fetus.
• Early fetal brains are smooth, but convolutions and invaginations develop by birth.

Stages of Neural Development

• Fetus: Neurogenesis (cell proliferation).
• Neurogenesis is the creation of new neurons from stem cells and primarily occurs during the 3rd and 15th week in utero but is limited in adulthood.
• This process increases & creates more cells by division of cells, resulting in gray matter.
• 7 months in utero: Synaptogenesis & Cell migration.
• Synaptogenesis is the creation of synapses between neurons and occurs from 20 weeks in utero until early adulthood.
• It happens after axons and dendrites are formed.
• Peak synaptic production in the cortex occurs around 8 months postnatal when infants have 40% more synapses than adults.
• Peak synapse number depends on the brain area, and most peak around 1 year.
• Synaptogenesis follows a "use it or lose it" rule.
• Visual cortex areas show developmental landmarks earlier than frontal cortex areas like in the synaptic density.
• Cell migration is the movement of newly formed neurons from the ventricular and subventricular zone to the final location, occurring from 4 weeks to 6 months in utero.
• Passive migration involves short distances where new cells push old cells in an outside-inside spatiotemporal organization via passive displacement.
• Active migration involves long distances in inside-outside spatiotemporal organizations and uses glial cells.
• Neurons use chemical signals (neurotransmitters) to determine when they have reached their final destination.
• Disruptions in migration can lead to mental retardation, schizophrenia, and autism.

Cell Elaboration

• Cell elaboration (differentiation), culling, and myelination peak at 4 years and continue into adulthood, affecting white matter.
• There is an increase in the size and complexity of the dendritic tree.
• First dendrites are seen around 15 weeks.
• The first synapses are seen around 23 weeks, and the process continues after birth.
• Culling is the loss of synapses because of lack of use or cell death.
• Myelination is the formation of myelin/fatty sheaths and occur from 5 months in utero through adulthood.
• It is critical for development and observable behaviors depending on that location, such as language in the temporal cortex and IQ in frontal areas .
• Myelin formation occurs when oligodendrocyte cells wrap around the axon, pruning grey matter and increasing white matter.
• Vision areas develop before language and decision and self-control areas.
• Cortical areas start forming prenatally but continue into adulthood.
• Peripheral areas develop first in motor areas and then in sensory areas.
• In the first year, the brainstem and cerebellum develop.
• By age 4, sensorimotor areas are completed.
• By puberty, the parietal and temporal regions (language, attention, memory) are complete.
• By early adulthood, the prefrontal and frontal areas (working memory, reasoning, decision making) are finished developing.
• Neurons themselves are grey matter, while myelinated axons are white matter, which connects brain regions for information transmission and makes up about 50% of the brain.

Socioeconomic Status

• Lower socioeconomic status is related to brain development and leads to lower SES is associated with smaller brain structures and differences in language and cognitive abilities.
• Factors such as education, nutrition, stress, and parent-child interactions contribute to these changes, which can be seen even before birth due to pregnancy complications, stress, and poor nutrition.

Brain Plasticity

• Brain plasticity enables adaptive changes in response to environment and experience.
• Experience-expectant plasticity reflects adaptations to experiences common to almost everyone.
• Experience-dependent plasticity underlies individual differences in brain organization and structure based on unique experiences.

Brain Areas

• The brain stem (involuntary) handles reflexes, balance, arousal, and cardiac and respiratory functions.
• It acts as a relay station for information to and from the brain.
• The cerebellum (body movement by choice) coordinates voluntary motor movement, balance, equilibrium, and muscle tone and potentially involved in memory.
• The occipital lobe is the is the center for visual information.
• After birth the visual cortex shows rapid development and reaches its synaptic peak density early.
• Most modules for processing information (colour, orientation, depth, size, motion) are functional by 3 months; orientation develops first.
• Orientation, a necessary component of object perception, shows some response by 6-8 weeks and reaches adult-like levels by 3 months.
• Colour processing shows functionality by 6 weeks and develops through the first year.
• Motion and binocular disparities onset between 7-12 weeks.
• The temporal lobe (perception) handles perception and recognition of objects, language, and memory skills.
• It exhibits activity to hiding and reappearance of an object at 6 months.
• There is face activity at 2-3 months, with more specialization throughout the first year.
• Speech-related activity starts around 6 months and strengthens during the first year.
• Activity in the two streams appear to have a related onset in the two streams, bit the dorsal stream exhibits protracted developmental process relative to ventral stream
• The parietal lobe (senses) contain two functional regions.
• Parietal lobe integrates sensory information into a single perception.
• It constructs a spatial coordinate system to represent the world.
• Parietal maturation occurs later than visual cortex maturation.
• Parietal lobe activity is increased at 3 months.
• Saccade related activity is not exhibited until after 6 months.
• Mental rotation tasks don't reach adult levels until the ages of 8-12 years.
• The integrating parts of a pattern or object does not reach adult level activity until 12-14 years The frontal lobe (smart) handles higher-order cognitive abilities, reasoning, decision making, planning, and working memory.

Anatomy

• Dorsal stream is associated with the metrics, motion, object location, information for eye movements and more and the person it blind to identity and function.
• Ventral stream is associated with shape, colour, identifying and recognizing forms and objects, and long-term memory.
• A stroke that causes damage to this stream results in visual form agnosia.
• Each stream is thought to have a different developmental timeline.
• Thought ventral stream processing development precedes dorsal stream development.
• Studies using structural MRI suggests similar developmental trends for parietal (dorsal) and temporal (ventral) areas, but these do not indicate functional development.

Heredity

• Heredity is the transmission of genetic information across generations and the genetic information translates into differences in physical characteristics and behavior.
• Statistical measure (h²) is a value that ranges from 0-1.
• It is calculated by dividing the variability in the genotypes of the individuals in a population by the variability in the phenotype
• Closer to one means most differences in phenotype stem from genetics.
• Closer to zero means most differences come from the environment.

Genes

• Example of environmental effects are the brothers of Bogota who have the same genes, they had different heights as a product of their environment.
• Genotype is all of the unique genetic makeup of the individual and comes from their parents.
• Phenotype is the observable traits/characteristics, influenced by the blend of genes and environment.
• DNA (deoxyribonucleic acid) makes up our chromosomes.
• Individuals differ by about 0.1% of DNA.
• Chromosomes are thread-like structures containing DNA located in the cell's nucleus. Segments of DNA are a basis for heredity
• Alleles are different forms of a gene, with two in each pair relating to the same characteristic but in different forms.
• Homozygous is when both parents give the same allele, the offspring will exhibit that trait.
• Heterozygous occurs when each parent gives a unique allele and the way in which the alleles interact determines which it is.
• Dominant alleles are expressed(trait the child has) non-recessive alleles are not(trait the child does not have)

Genetic Inheritance

• Genetic inheritance is determined by the parents chromosomes and genes.
• Autosomal dominant requires one dominant allele to express the phenotype.
• It makes no difference if alleles are homozygous vs heterozygous for those with this trait.
• If a child has a recessive allele, they will be a carrier and can pass it to their offspring.
• Autosomal recessive requires both two recessive alleles to express (both parents must give the recessive allele).
• Heterozygous parents are carriers for the recessive allele.
• Codominance occurs when two distinct dominant alleles are expressed (phenotype differs from either parent).
• Incomplete dominance is the blend of the two and phenotype differs again.

Behavioral Genetics

• Behavioral genetics studies how one's genetic markup and environment affect behavior.
• Twin studies compare traits between identical and fraternal twins; if the phenotype is heritable, identical twins will be more similar.
• Adoption studies look at phenotype similarities between a child and their biological/adoptive parents.
• Twin-adoption studies compare adopted twin pairs in terms of phenotype.
• John Constantino and colleagues, 2017 compared looking behavior in identical vs fraternal twins assessing eye-mouth engagement.
• They found that early social engagement is influenced by genes.
• Camille Cioffi & colleagues 2020 studies kids adopted to measure child ability to regulate their ability to regulate their attention.
• Infants with low parental inhibitory control tended to do lower the control.
• Warm adaptive mothers had babies with better inhibitory control.
• This means that both influence gene and environment.

Factors

• This means that both influence gene and environment.
• Gene-environment correlations occur when gentically influenced traits evoke or elicit environmental responses.
• Passive gene-environment correlations the parent gives genetics and the environment to the child.
• Evocative gene-environment correlations are triggered by genetic characteristics.
• Active gene-environment correlations exist when the child seeks environement to suit traits.
• Gene-environment interactions occur when genes makes someone more sensitive to environmental actors.
• Orchid children refers to high genetic sensitivity to adverse events
• Dandelion children are thriving in all conditions.
• Epigenetics refers to change in gens expression with changing the DNA from things as diet, stress, etc.
• A wwII study in the the Netherlands found in the Netherlands famine was added to fetus' to adopt malnutrition. These adults entered obese.

Visual Attention

• Attention needs to select a target.
• The thinking this measures is but attention is really complex.
• Habituation novelty preference.
• Cohen suggested 2 components: attention getting, and attention holding, and measured latency and duration in chessboard.
• Larger patterns captured them quicker.
• Did not seem to impact speed but more time was looking
• After attention-getting. Cohen suggests attention-holding.
• Suggest that is making orientation heart rates will go down. During attention rates remain down, and infants are less likely to be distracted.

Selective Attention

• This relates to studies that only give one or two stimuli.
• Visual pop out = stimuli with a distinct property that allows for them to gain attention.
• Used preferential looking with looking to see the pop out
• In the 90S's found 102 months did pop out
• The difference was huge!!
• In 2006 with l among + to pick on L
• When L is + they take longer
• W- presence is do not longer with l Same is true with kids, at that time you ignore the other stimulus Had 198s when 4- month-year old 2 with to the image that superposition Then split where look Indicates attendance by selecting them

Perceptional

• The process of percepts become major in the first year. All guided by perception
• Newborns do see colors!! Newborn infants that are from 15 babies look longer