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Brain Development/ Plasticity - Coggle Diagram
Brain Development/
Plasticity
Brain Development
Prenatal development happens in 3 distinct stages: germinal (first 2 weeks), embryonic (weeks 3-8) and foetal period
The neural tube, which will become the brain/spinal cord, closes at 3 weeks of gestation.
Systems that are undergoing rapid change are susceptible to disruption- teratogens.
environmental influences
Teratogens:
Any agent that can produce a birth defect or increase the incidence of a defect in a population, following fetal exposure during pregnancy.
Teratogenicity depends on critical periods of development (timing), dose of drug/chemical, and duration of exposure.
chemical: methylmercury
Mothers whose diets primarily consist of foods contaminated with mercury (like fish).
Congenital minamita disease > brain disease and abnormalities caused by prenatal exposure
Microcephaly > ataxia, seizures, cognitive delays
Cognitive, behavioural and learning difficulties due to underdeveloped brain.
infection: zika virus
Spike of microcephaly cases began in Brazil in 2016.
Carried by mosquitoes
Highest risk of birth defects from virus is during 1st trimester
Cognitive and learning impairments
drug: alcohol
Fetal alcohol syndrome > growth restriction, facial dysmorphology, microcephaly, cognitive/learning impairments.
brain development
Stages occur in a serial format, but overlap with each other.
Involves a series of overlapping processes that begin prenatally but continue until late adolescence.
STAGE 3: migration
6 weeks to 24 weeks.
Neurons move to their final destinations (different brain lobes) from the proliferation area.
The brain develops from back to front, inside out. prefrontal/frontal cortex is last because the neurons have to make their way through the whole brain.
Neuroblasts “ride” glial cells
Not well understood how neurons know where to go > where they “live”
DEFECTS
Lissencephaly
(smooth brain)
Agenesis of the corpus callosum
The major fibre tract that connects the left and right hemispheres.
There are smaller tracts beyond the corpus callosum that connect the hemispheres, so the brain can adapt to not having it.
STAGE 4: circuit formation
Communication between neurons that arrive in their places after migration.
Axons are the primary mechanism by which neurons transmit to other neurons.
Dendrites are the receptive areas of the neuron.
Both axons and dendrites increase in number with development.
Synaptogenesis
Synapses are the gaps between one neuron's axon and the other’s dendrites.
Synaptogenesis is most rapid during pre- and early postnatal periods (begins around 23 weeks)
Overproduction > infants have many more synapses in their brains than adults do.
The peak number of synapses occurs postnatally at different times across different brain regions.
Pruning
The way we get down to the adult level of synapses.
Experience determines which synapses will live or die > use it or lose it
The timing of pruning also varies across brain regions.
DEFECTS
Williams syndrome
Rare genetic disorder, distinctive facial features > elfin
Indiscriminate friendliness, highly verbal, cognitive delays and learning challenges
Failure in pruning, synaptic density remains at infant levels, preventing the brain from adapting to experience and becoming specialised in processing the information it's exposed to.
STAGE 2: neurogenesis (proliferation)
Begins around the 5th week, and peaks at 3-4 prenatal months
New neurons form from neural stem cells
Supporting cells called glia are being created
Hundreds of thousands of new cells created each minute.
DEFECTS
Microcephaly
(small brain) > brain does not produce enough neurons
Rubella, methylmercury, zika, and high levels of vitamin A
Macrocephaly
(big brain) > congenital disorder (cranial pressure); genes that regulate proliferation do not turn off > brain produces too many neurons.
STAGE 5: myelination
Formation of the myelin sheath around axons to increase signal transmission speed.
Myelin is a lipid/protein substance produced by supporting cells (glia)
Myelin insulates axons so that signals can travel faster.
Myelinated is white matter, non-myelinated is grey matter.
STAGE 1: neurulation
3rd week after conception
The neural tube forms from ectoderm, which will develop into the central nervous system.
The neural tube closes from the middle outward
DEFECTS
Anencephaly
: the top tube (brain area) fails to close > not a condition that babies survive due to the brain not being able to control respiration. Once found will usually result in termination of the pregnancy.
Spina bifida
: a section of the spinal cord is exposed through the back due to a failure in the closure of the lower part of the neural tube.
Folic acid is important in preventing neural tube defects.
Developmental
Plasticity
experience and brain development
Experience dependent
Changes in the brain that occur in response to learning experiences that are unique to the individual
Allows that organism to learn/adapt to their specific environment throughout the lifespan
New synaptic connections are formed with learning
Experience expectant
Changes in the brain that occur in response to expected species-typical experience (eg language, music, faces, etc)
Involves critical or sensitive periods early in life
Initial overproduction of synapses that is followed by synaptic pruning
Perceptual narrowing
Example for domain-general plasticity that is common to all components of human communication
The human brain has evolved to expect communication-related experience; it adapts to the unique form that communication takes in the culture that it was born into.
SIGN LANGUAGE (Palmer et al 2012)
Baby’s spot the same categorical boundary between two hand signs that ASL learners do.
Hearing 4 month old infants (but not 14 month olds) perceive sign boundaries categorically.
Hearing infants growing up with ASL (12-18 month olds)
Infants learning ASL retain the ability to discriminate sign boundaries.
AUDITORY SPEECH (Werker and Tees 1984)
Around 9 months of age infants lose the ability to discriminate between speech contrast that are not part of their native language
Conditioned head turn procedure
Kuhl, Tsao and Liu (2003)
9 month old infants exposed to either mandarin or english
12 sessions, 25 min each, over 4 weeks (approx 5 total hours) of story reading and play
Test ability to discriminate mandarin contrasts
better to do in person than on video > results in better discrimination
AUDIOVISUAL (Weikum et al 2007)
Languages look different.
4 and 6 month olds can discriminate between languages with the sound turned off, but 8 month olds cannot
Longitudinal studies of monolingual (english) vs bilingual infants (english/french), tested at 6 and 8 months.
Experience with both languages allows bilingual infants to retain the ability to discriminate between them at 8 months
FACES (Heron-Delaney et al 2011)
Young infants can discriminate between faces of any race, but lose this ability by 9 months
“Other race” effect
Train caucasaions with picture books containing either caucasian or chinese faces between 6 and 9 months
Looking time
Reversing perceptual narrowing
8-10 month old babies who had already lose the ability to discriminate between asian faces had video exposure to those faces
Tested with female and male faces after first lab, and then 1-2 and 3 weeks later.
look at doc for sugita study
MUSIC RHYTHM (Hannon and Trehub 2005)
Rhythms that characteruse music are cultural specific
Balkan rhythms are non-isochronous
Western 6-month old infants can discriminate rhythms from all cultures > western and Balkan
Western 12-month olds cannot discriminate between Balkan rhythms
Training: train babies twice a day with a CD of Balkan music for two weeks > test at 12 months.
Same amount of training made no difference to adults ability > there is a critical period of early development during which plasticity is open and training works.
Developmental cognitive neuroscience
Electroencephalogram (EEG)
> sensors placed on the scap to record tiny electrical signals generated by the brain.
Event-related potentials (ERPs)
Event-related = in response to a stimulus
High temporal resolution > good for assessing when brain activity changes corresponding to the event.
Low spatial resolution > cannot give accurate answers about brain region responsible for signal change.
Dips and troughs in the waveforms are read for analysis
Amplitude = how big they are
Latency = how fast they are
Kuhl - Does experience shape the way the infant brain processes speech contrasts?
7 month old and 11 month old infants
Measure brain activity in response to native and non-native speech contrasts > ERPs
Analysis of brain activity lines up with synaptic pruning