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Psychology 3325 Lecture Notes - Ct Scan, Positron, Photon

Course Code
Psychology 3325
John Usher

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Visualization Methods:
brain exhibits plasticity structural change resulting from experience:
new synapses form, old ones disappear, dentrites grow and shrink and oxons of neurons
become myelinated
physiopsychs can trace effects of physical maturation and plasticity by using techniques that
mark or stain neruons chemically
can part percentage of neurons, making their dentrites prominent so that they an estimate
the growth of dentrites and infer possible changes in number of synapses
other stains could highlight axonal growth, showing how axons grow to connect with
specific areas of brain
also used to examine large portions of brain when human patient dies from brain injury
can use dye to locate injury
until recently most useful technique of brain imaging was CT Scanner (compurized
tomography) device that uses special X-ray machine and computer to produce images of
brain that appear as slices taken parallel to top of skull
scanner sends narrow beam of X-ray through patient's head and is then moved around
head while computer calculates amount of radiation passing through it at various points
along each angle
results in 2D slice of head parallel to skull
can determine approximate location of brain injury
2 other recent developments:
positron emission tomography (PET) - relies on radioactive substance which is incorporated
into brain tissue metabolically, where it emits an antimatter particle (positron)
positron travels 2 cm through brain before it collides with matter particle causing
emmission of photon which can be measured and used to construct brain image
magnetic reasonance imaging (MRI) produced by plaing individual in strong magnetic field
causes molecules within its influence to become aligned with lines of magnetic force
radio signal is then generated around person which has effect of tilting these aligned
atoms (just as you might nudge spinning top to wobble)
scanner measures time it takes molecule to stop wobbling and recover to aligned state
because different molecules take different times to recover an image can be constructed
based on relative amounts of different materials within scanner
eg. myelinated axons recover at different time than unmyelinated producing contrast
between white and grey matter
produce high resolution images of brain regions and are safe to use (no radiation)
Paus used MRI to trace development of white matter as children matured into
one study found evidence of plasticity resulting from learning to drive taxicab in London
Functional Measurement
measure neural acitivty as brain performs some function combines knowledge of brain's
physiology and visualization technology
eg. functional MRI (fMRI)
measures different recovery times of blood hemoglobin
Hb reacts to magnetic field of MRI but its recovery time after radio signal is applied
depends on whether it has released its complement of oxygen
contrast of oxygentated and deoxygenated Hb can be measured in MRI very quickly,
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