Psychology 2115A/B Lecture Notes - Lecture 4: Positron Emission Tomography, Visual Cortex, Radioactive Tracer

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Chapter 4: Cortical Organization
May 26, 2016
Exploration of Spatial Organization
Electronic map on V1
Retinotopic map is an electron map of the retina on the cortex
Cortical magnification – a small area of the fovea is represented by a
large area on the visual cortex
You need more brain to process fovea vision then peripheral vision
The little divot it the fovea
Fovea is 8-10% of the cortex
If staring at someone’s nose, seeing the image on the primary visual cortex would
show a huge nose and everything else becomes really tiny (like a funhouse
mirror)
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Monkey brain after being put to sleep
Inject animal with dye taken up by active neurons so if neurons are more active,
they take up more dye (ex: very active neurons will dye darker than those who
aren’t doing much)
Keep the animal looking
Then euthanize the animal while it’s asleep and remove the primary visual cortex
to see that the same pattern is seen on the animal brain that the monkey had been
looking at however it’s only half of the original circle because we split everything
in half in the brain (massive over representation of the central vision)
Brain Imaging Techniques
Positron emission tomography (PET)
Person is injected with a “harmless” radioactive tracer (ex: glucose)
Tracer moves through bloodstream
Monitoring the radioactivity measures blood flow
Changes in blood flow show changes in brain activity
In the process of decay, gamma rays are released and go off in
different directions, hit opposite sides of the detector and computer
will draw a line through your head
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PET - subtraction method
Brain activity is determined by:
Measuring activity in a control state (ex: dots not moving)
Measuring activity in a stimulation state (ex: dots are moving)
Subtracting the control activity from the stimulation activity
Difference shows where brain is processing a particular thing
being studied
Problems: temporal (time) and spatial (where in brain)
resolution, doesn’t work for every brain type/size
Functional magnetic resonance imaging (fMRI)
Hemoglobin carries oxygen and contains a ferrous molecule that is
magnetic
Brain activity takes up oxygen, which makes the hemoglobin more
magnetic
fMRI determines activity of areas of the brain by detecting changes in
magnetic response of hemoglobin
Very high spatial resolution image and collect brain activity much
faster than in a PET scanner
Subtraction technique is used like in PET
The Cortex is Organized in Columns
Cortical magnification factor
Fovea has more cortical space than expected
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