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Lecture 2

PSYCH211 Lecture Notes - Lecture 2: Motor Cortex, Myelin, Walter Jakob Gehring

Course Code
Mathieu Le Corre

of 4
Lecture 2: JAN.9TH.2013
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
All neurons born by 28th 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 7th 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
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 depends on location of damaged area
Equipotential malleable clay:
o Completely recover
Left Hem damaged at birth:
Don’t perceive details and sometimes don’t recover function but can see global form
o Some brain function is fixed at birth and not malleable
Right Hem damaged at birth:
You see details and some global form
Initially impaired but some recovery
So reorganization can happen but it takes a while (for space)
- Brain continues to develop after birth
- Different areas of brain develop at different points
Lecture 3: JAN.16TH.2013
Genes: Basic Organization
Cell 23 pairs of chromosomes genes DNA (made up of 4 chemical letters)
DNA is in nucleus of our cells
Every cell in our body contains our full genetic material/genetic instructions that built our entire body and brain
DNA is everywhere
Genes & Development Two Problems:
1. Human body & brain extremely complex, yet very few genes (10,000). How can so few genes build body/brain?
2. Genes produce proteins. Brains are made of millions of proteins coordinated in exquisite order. How put pieces
1. A tiny number of genes:
Great surprise of human genome project: human have only about 10,000 distinct genes
Seemed like too few to build human brain and body
Assumption: each gene has a single function, and just obstinately performs that single function
o Is this true?
The same gene can have variable effects:
o Effect of blocking “memory protein gene” depends on location of gene in the brain
In hippocampus blocking prevents maze-learning (spatial memory)
In amygdala blocking prevents learning to fear a tone that predicts a foot shock (emotional
learning) EX. Prevents animals from hearing a dangerous sound which allows them to run
away from that danger
2. What genes do: Code for Proteins…
Genes don’t “see” any further than the protein(s) they code for
Genes build complicated structures by cooperating
Genes are mini-orchestras
o Some genes are conductors
o Others are musicians