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Lecture 2

PSYCH 211 Lecture 2 and 3 NOTES (Genes & Brain Development)(Jan.14 & Jan.16 2013)

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University of Waterloo
Mathieu Le Corre

TH Lecture 2: JAN.9 .2013 BRAIN DEVELOPMENT: 1. Brief overview of adult brain structure 2. Steps and processes of brain development from fetus to adolescence 3. Are genes involved in learning? 1. Brief overview of adult brain structure  High level of organization of the human brain which is the same for everyone o EX. When one person is planning or deciding something, the brain activity is in the frontal lobe but it is the same for everyone – brain activity in frontal lobe The Retinotopic Map:  Presented wheel + spokes pattern in right visual field of anesthetized monkey with one eye closed  Injected “dye” that marks neurons when they are active  Took slice of visual cortex How does all the structure develop?  From single cell to full brain – general principles of brain building  How much of the course of brain development is fixed from birth? Neurons – Three General Problems:  Making neurons o General process o Axonal & dendritic growth  Getting them to the right place  Hooking them up the right way Neurulation: Making Neurons  Neural Plate – part of zygote (first bunch of cells) that becomes brain & spinal cord  At 10 weeks, neurulation starts – production of neurons  240,000 neurons/minute (at peak) – 4,000 neurons/sec th  All neurons born by 28 week  When the brain grows, the front becomes the back and starts folding Cerebral Cortex – thin outer layer of the brain  Made of six distinct layer of cells  Grows from inside out – neuron migration o Start with innermost layer o Work way up on supporting cells o Make all 6 layers this way o Have all 6 layers by 7 month after conception Brain = massive network of networks of interconnected neurons Not true that brain development is done when we are born – major changes in brain organization that happens well into adolescence (so our brains right now are almost done developing)  Size of brain is developed at birth  Neurons are all made by 28 weeks but dendrites keep growing (branches that receive info) Two extreme ideas/hypothesis: 1. Equipotentiality (equal potential) Hypothesis  Can take any neuron at birth and make it do anything  No neurons are not assigned to anything yet at birth – no predestined function o Determined by the accidents of experience  No structure of brain – all determined by experience 2. Innate Architecture Hypothesis  Each neuron already know it’s function and it can’t change its mind from the beginning  Brain organization entirely fixed at birth Synapses:  when you are born there are more synapse connections in a 2-year-old than a 25-year-old  some connections go away over development Making Synapses:  Once cells are located, must make connections with others  To make synapses, each cell grows its dendrites and its axon and terminal buttons  Process starts a little before birth  Ends after birth Synaptic Pruning:  In neonates, synapses are overabundant o Excess connections between different perceptual areas (visual & auditory cortex)  40% of synapses will be eliminated by pruning o As many as 100,000/s at peak periods  Rates of synaptic pruning depends where it is in the brain Myelination (white matter) (grey matter – cell body)  “Insulating” neurons – increases speed of conductivity  Depending on how much myelin is covering the axon depends on how fast information is passed  Starts prenatally, continues until early adulthood  Time when myelination begins depends on different areas of the brain  Also area-specific o Sensory areas then motor areas and “association areas” o Prefrontal cortex (involved in planning, inhibition, working memory) is last (adolescence) Is brain development malleable or is it fixed from birth?  Malleable – brain is clay molded by experience o At birth, brain structure/function is uniform o Adult brain organization is product of experience o “Equipotentiality” – any part of the brain can do any function  Fixed – innate architecture o Brain structure and organization is determined by genes and is fixed at birth  Various pieces of evidence suggest that there is some innate architecture but also some malleability Evidence for some fixed:  Overall distribution of functions is the same for all humans  Effects of perinatal brain damage on spatial perception o Lateralization of spatial processing in adults  Global form (the “M” and the triangle) – right hemisphere  Local details (e.g. the Z’s that make up the M) – left hemisphere What is the effect of damge at birth?  Fixed architecture: o Complete loss of function o Effect depen
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