Book: The imaged brain 1

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What are two methods of structural imaging?
CT and MRI
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What does CT stand for?
Computerized tomography
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what does MRI stand for?
Magnetic resonance imaging
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What is the principle of structural imaging?
Measures the spatial configuration of different types of brain tissue (e.g. skull, grey/white matter, fluid), which have different physical properties. Construct static maps.
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What is the principle of functional imaging?
Measures temporary changes in brain physiology associated with cognitive processes i.e. dynamic, not static
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What are two methods of functional imaging?
fMRI and PET
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How do MRI scans differ from CT scans?
1) No xray, 2) can differentiate between grey and white matter 3) experimental not clinical setting 4) skull not white
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Benefits of MRI?
1) No ionizing radiation; safe 2) Better spatial resolution e.g. gyri 3) Discriminates between grey and white matter 4) can be adapted to fMRI
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How does fMRI differ from MRI?
When neurone activity increases, blood supply to that region increases. fMRI measures oxygen in blood
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How does PET differ from MRI in measuring blood supply?
PET measures change in blood flow to a region directly, whereas fMRI is sensitive to the concentration of oxygen in the blood
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How does PET work?
PET uses a radioactive tracer bound to glucose or oxygen and follows blood to active areas
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How does fMRI actually detect the oxygen in the blood?
fMRI measures regional levels of blood oxygen by detecting magnetic changes in red blood cells when they become de-oxygenated
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List 5 step sequence of fMRI process/how it works
1)Protons spin with magnetic charge 2)Add strong magnetic field to line up protons 3)Add radio wave to orient them to 90deg 4)Protons resonate differently 5)fMRI compares oxy and de-oxy blood
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What can't go in an MRI scanner?
Metal of course!
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Does MRI or fMRI have better spatial resolution?
MRI (1x1x2mm), compared to fMRI (3x3x3mm)
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What are T1 and T2 images?
T1: structural - relaxation time; T2: functional - local interactions/eg deoxyhaemoglobin
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when neurons consume oxygen they convey ... to ... ?
oxyhemaglobin to deoxyhemaglobin
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what is special about deoxyhemaglobin?
Deoxyhemaglobin has strong paramagnetic properties, which introduces distortions in the local magnetic field. This distortion can then be measured i.e. the concentration of deoxyhemaglobin in the blood.
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what is the technique for measuring the concentration of deoxyhemaglobin in the blood?
BOLD
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what does BOLD stand for?
Blood oxygen-level-dependent contrast
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what does HRF stand for?
Hemodynamic response function
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what is the BOLD contrast?
The signal measured in fMRI that measures the concentration of deoxyhemaglobin in the blood
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what are the three phases of HRF?
1) Initial dip 2) Overcompensation 3) undershoot
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How is HRF plotted - what do the x-axis and y-axis measure?
x-axis - time; y-axis - BOLD signal
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What is the component of HRF that is usually measured in fMRI?
the peak - the overcompensation
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compare the temporal resolution of fMRI to PET
fMRI: 1-4 seconds; PET: 30 seconds
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compare the spatial resolution between fMRI and PET
fMRI: 1mm; PET: 10mm
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compare participant scanning frequency between fMRI and PET
fMRI: participants scanned many times; PET: scanned once
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Name three ingredients of a BOLD contrast
CMRO(2), CBF, CBV [cerebral metabolic rate of oxygen, cerebral blood flow and cerebral blood volume]
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What is the % signal change in a HRF?
0.5-3%
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Main problem with fMRI?
Brain is always active: need a baseline
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what is cognitive subtraction?
An experimental design in fMRI in which activity in a control task is subtracted from activity in an experimental task
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what is pure insertion?
the assumption that adding a different component to a task does not change the operation of the other components
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what are interactions?
the effect of one variable upon another
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what is functional integration?
the way in which different regions communicate with each other
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what does efMRI stand for?
event-related functional magnetic resonance imaging
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what is a block design?
stimuli from a given condition are presented consecutively together
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what is an event-related design?
stimuli from two or more conditions are presented randomly or interleaved
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what is stereotactic normalisation?
the mapping of individual differences in brain anatomy onto a standard template
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what is 'smoothing'?
redistributing brain activity from neighbouring voxels to enhance the signal-to-noise ratio
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what does VBM stand for?
Voxel-based morphometry: A technique for segregating and measuring differences in white and grey matter concentration
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What does DTI stand for?
Diffusion tensor imaging: Uses MRI to measure white matter connectivity between brain regions
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Card 2

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What does CT stand for?

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Computerized tomography

Card 3

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what does MRI stand for?

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Card 4

Front

What is the principle of structural imaging?

Back

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Card 5

Front

What is the principle of functional imaging?

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