Download 02_Neuroscience

Cognitive Neuroscience:
How the Brain Works
EDIT 600
Summer 2009
Instructor: Elise Christopher
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Neuroscience:
A New Phrenology?
1. Phrenologists:
“everything about a
person can be sussed
out by feeling bumps on
head”
–
Personality, Self-Esteem,
Music Ability, etc
2. Neuroscience today is
locating many functions
in specific areas of the
brain
–
Emotion, Memory, Face
Processing
3. Integrationist: Neural
Network Model of brain
http://en.wikipedia.org/wiki/Phrenology
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The Principle of
Single Dissociation
1. Personality:
Phineas Gage
2. Memory: HM
3. Emotion
Recognition: SM
http://www.ninds.nih.gov/health_and_medical/pubs/tbi.htm
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The Neuron
1. Basic unit of the
brain
2. Humans have 100
billion neurons
3. Computer model:
•
•
•
•
Dendrites =
transistors
Neuron = microchip
Brain regions =
embedded systems
Brain =
supercomputer
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The Neuron
1. Basic unit of the
brain
2. Basic form of
communication is
electricity
•
•
Intra-Neuron
Communication:
Action potentials
Inter-Neuron
Communication:
Through the
synapse
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Intra-Cellular Communication:
The Action Potential
1. Action potentials are
electrical signals
2. Ever wonder why we
crave salt?
•
Cell membranes
3. Sodium-Potassium
(Na+-K+) pumps
•
Responsible for
changing the brain’s
electrical potential
1000s of times per
second
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Inter-Cellular Communication:
Neurotransmitters
1. Neurotransmitters
are chemical signals
2. Action potential
triggers their release
into synapse
3. Receptors on
receiving neuron pick
up neurotransmitters
•
Triggers action
potential in receiving
neuron
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Neural Networks
1. Neuronal
Communication
2. Early thought:
•
•
On/Off Switches
Binary Notation
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Neural Networks
1. Neuronal
Communication
2. Current thought:
•
Neural nets with
weights
3. Neural weights
change
•
Rescorla-Wagner
Model
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Across the Brain
“It was looking
at me! What
should I do
about it?”
“What
was
that?”
“I’ll go talk
to her.”
STS
V1
pFC
Amyg
FG
“That was a
face. Was it
emotional?”
“Yes, it was
happy.
Where was
it looking?”
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Methods to Study the Brain
1.
2.
3.
4.
5.
–
Postmortem Studies
Animal Studies
Electrical Recordings: EEG/ERP
Metabolic Imaging: PET
Static Imaging Techniques: fMRI
Stimulation Techniques: TMS
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Neuroscience Methods
1. Observational vs. Correlational Methods
2. Observational:
•
•
Postmortem Studies
Lesion Studies
•
•
•
Electroencephalography (EEG) / Evoked-Response
Potentials (ERP)
Functional Magnetic Resonance Imaging (fMRI)
Positron Emission Tomography (PET)
•
•
Transcranial Magnetic Stimulation (TMS)
Animal Studies
3. Correlational:
4. Experimental Methods
5. Time constraints, spatial constraints, subject
comfort constraints
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Postmortem Studies
1. Identify disorder
and then examine
after death
• Alzheimer’s
Disease brains
2. Pros:
• Direct observation
of brain
3. Cons:
• Cannot run more
studies of behavior
on subject
www.alzheimer.ca
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Lesion Studies
1. Removal of area of
brain results in single
dissociation
2. Pros:
•
Very reliable measure
of brain-to-behavior
3. Cons:
•
•
Lesion sites often vary
widely
Subjects sometimes
have other deficits
that go along with
brain injury
Adolphs, Tranel & Buchanan (2005).
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Nature Neuroscience 8, 512 - 518
Electroencephalography (EEG) /
Evoked-Response Potentials (ERP)
1. Measures local
field potentials of
populations of
neurons
2. Pros:
+7V
• Highly timesensitive
3. Cons:
• Spatially
insensitive
100m
s
-4V
• Inverse problem
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Functional Magnetic Resonance
Imaging (fMRI)
1. Huge magnet sends
pulses through brain
•
•
Iron-rich hemoglobin in
blood responds
strongly
De-oxygenated blood
responds weakly
2. Assumption: Brain
areas with more
blood flow have been
more active recently,
so they must have
been active in task
You go here
neurophilosophy.wordpress.com
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Functional Magnetic Resonance
Imaging (fMRI)
1. Pros:
• High spatial
sensitivity
• Down to the mm!
• Contrast ability
• Negative vs.
Positive Activity
2. Cons:
• Poor time
sensitivity
• As much as several
seconds
www.sciencemuseum.org.uk
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Positron Emission
Tomography (PET)
1. Radioactive material
is injected
2. Participant then
scanned to produce
an image of the
brain’s activity
3. Pros:
•
High spatial sensitivity
4. Cons:
•
•
Poor time sensitivity
Subject must be
injected
health.howstuffworks.com
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Transcranial Magnetic
Stimulation (TMS)
1. Pulses of magnet to
weaken or inhibit
function in areas of
brain
2. Pros:
•
•
Non-correlational method
Definitive measure of
brain-to-behavior
3. Cons:
•
•
Can be slightly
unpleasant/painful to
muscles
Long-term repercussions
unknown
www.physpharm.fmd.uwo.ca
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Animal Studies: In Vivo
1. Monitor activity of
a single neuron
2. Pros:
• Observing cell
while firing is very
reliable
3. Cons:
• Limited sample
size due to
delicacy of
equipment
http://www.vis.caltech.edu/~zoltan/
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Cerebral Cortex Principles
1. Contralaterality
• Right side of brain controls left side of
body
• Left side of brain controls right side of
body
2. Corpus Callosum
• Neural fibers connecting left and right
lobes
• Allows communication between right
and left sides of the brain
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Cerebral Cortex Principles
1. Localization of function
• Specific mental processes are
correlated with discrete regions of the
brain
2. Hemispheric Specialization
• Each lobe of the brain has specialized
functions
• Ex: Language on the left
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Lobes of the Cerebral Cortex
1. Frontal
• Reasoning & Planning
2. Parietal
• Touch, Temperature, Pain, & Pressure
3. Temporal
• Auditory & Perceptual processing
4. Occipital
• Visual processing
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Neuronal Communication
• A really cool video of neuronal
communication can be found on YouTube:
• Neurons-HowTheyWork
– Try to remember that the brain doesn’t
actually have those sound effects!
– Thought Question: Why does it make sense
for the creators of this video (Discovery
Channel) to use these sound effects when
illustrating the brain?
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