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PSYCH 1XX3 (384)
Chapter 1

Ch. 1 - Neural Development notes.docx

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Christopher Teeter

Neural Development • Prenatal Development of the Nervous System • Nervous system starts developing about 3wks after conception with the formation of primitive neural tissue (neural plate)  neural plate folds and closes to become the neural tube  leads to devel. of brain and sc • Neural tube lined with neural stem cells – give rise to all cells of the nervous system • Basic regions of the brain: forebrain, midbrain, and hindbrain are visible by about 28 days – looks distinctly human by 100 days – forms sulci and gyri around 7mths • Effect of Prenatal Environment:  Nutrition: º Neural tube defects are the most common type of birth defects – can be fatal o If the tube fails to seal at the head of the embryo, the cerebral cortex doesn’t develop (anencephaly) – always fatal o If the tube fails to seal at the lower end, part of the sc may develop out of the spine (spina bifida) – ranges in severity – symptomless to highly disabling with paralysis and sensory loss º Chance of neural tube defects can be greatly reduced if mother takes folic acid prior to conception – vit. B found in large amounts in leafy veg., legumes, liver, and sunflower seeds  Teratogens: º Can cause neural tube defects º Can have an effect at any point during pregnancy – the earlier a fetus is exposed, the more harm can be done – inc. vulnerability in early pregnancy º Most common one is alcohol – if a mother drinks, the fetus is receiving the alcohol through the mom’s blood – drinking heavily may result in birth defects such as Fetal Alcohol Syndrome (FAS) – causes structural and functional abnormalities of the nervous system º Until fetus shares mother’s blood supply (about 10 days after conception) it is safe from the effects of alcohol º Contracting the flu during pregnancy may inc. the risk that the baby will develop schizophrenia as an adult º Severe maternal stress (ex. living through an earthquake) inc. risk of baby developing depression as an adult º Flu and severe stress can act as teratogens and disrupt the development of the brain  Sensory Experience: º Vision is often considered to be the primary sense in mature and sighted adults º At birth the visual system is relatively immature – womb is devoid of visual info º Prior to receiving any visual info, neural pathways in the developing visual system are restructured and highly organized – spontaneous patterned activity in the retina helps to strengthen and organize the connectivity of the visual system – prepares the brain for the visual world by mimicking the basic patterns of input that the system can expect to see when individuals first open their eyes º Audition is fairly mature at birth – primary auditory components (ex. cochlea) have nearly fully developed – uterine environment can be as loud as 80 decibels (volume of a crowded dance floor on a Saturday night) – infant can differentiate a recording of their mother’s prenatal womb sounds from another mother’s º Sounds below 500Hz (ex. lower ranges of the human voice, violas, cellos, etc.) can be detected by the fetus in the womb with a small degree of attenuation (dec. in intensity) / Sounds above 500Hz cannot be detected – can hear dad’s voice but not mom’s in womb º Chemical sensory info from mom’s diet travel to the fetus through amniotic fluid and are swallowed by the fetus – develop sense of taste and smell – these prenatal flavour experiences can influence the post-natal flavour preferences – babies whose mothers drank carrot juice during pregnancy showed more enjoyment of carrot- flavoured cereal when they first tried it than babies whose mom’s drank water during pregnancy • Post-natal Development of the Nervous System: Infancy and Childhood • Brain Development: Synaptic Development  In the first few months there is a rapid inc. in the number of synapses – at 1yr and until 10yrs the number dec. (synaptic pruning) – ensures the strongest and most useful survive  Some of the extra connections are functional – in response to spoken language a newborn’s brain responses show activity in the auditory and visual cortexes – doesn’t disappear until 3yrs – infant may experience sensory info in an undifferentiated manner • Brain Development: Role of Experience  Rapid inc. and dec. in synapses is a method of sensory stimulation – if one sense doesn’t receive stimulation, the extra connections are left open, so that the deprived sense can be supplemented by connections to other intact senses - if an infant is born without a particular sense (ex. vision), the brain can adapt by maintaining the “extra” connections between the visual and tactile areas that might otherwise be pruned – allows individual more neural processing surface area ad a finer detailed representation of the world through the sense of touch (“see with their hands”) – in individuals blind from a very young age, the visual cortex is active when reading braille and performing other tactile tasks  Rats raised in an enriched environment (more sensory stimulation) are better at problem solving tasks such as mazes – have inc. complex neurons with more dendritic space than rats raised in a barren environment (lack of sensory stimulation) • Experience-Expectant / Experience-Dependant • Visual cortex is organized into ocular dominance columns that synapse with neurons carrying info from each eye • Area of dominance columns is the same for both eyes in sighted people – receiving input from both eyes is experience-expectant – brain expects same strength of input from each eye • If an animal has atypical visual development and one eye sends more input than the other, visual connections to each eye will be imbalanced – whether the visual system connections and structures develop typically is experience-dependant – only develop typically if animal receives the appropriate input • David Hubel and Torsten Weisel (won the Nobel Prize) found this wh
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