Biology - Lecture 2 (BOLD signal)
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- Created on: 28-03-16 18:10
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- Lecture 2 - BOLD
- BOLD signal
- MRIs use magnets and measure the BOLD signal (blood oxygen level dependent signal) - (Journey of blood, where is it going?).
- Neurons: how the brain talks to itself. Blood flows to different parts of the brain to give them oxygen, in turn keeping cells alive.
- The more activity there is, the more oxygen they need.
- By measuring the oxygen needed at one place you can see how much activity is going on, easy to spot problems in brain. BOLD signal is slow.
- Haemoglobin
- Every blood cell carries a molecule of haemoglobin, and oxygen binds to haemoglobin, which is how oxygen moves around in the blood. “Petrol station”.
- Haemoglobin responds differently to magnetic field (which are used in MRI) depending on whether or not its got oxygen with it.
- Haemoglobin with oxygen = oxyhemoglobin. Haemoglobin without oxygen = deoxyhaemoglobin, and is more attracted to magnetic field.
- The less disruption in magnetic field of the MRI (think of magnet and Fanta bottle) = oxygenated blood, and more signal in MRI scan.
- Reduction in the difference in the field means an increase in signal received means an increase in signal in MRI. No disturbance = oxygen flows.
- fMRI
- fMRI does not measure brain activation; it measures blood flow (destination of blood, where is blood going).
- In fMRI, BOLD signal is arbitrary (means it is inconsistent, no stable base rate to measure against).
- Looking at difference in magnetic property rather than difference in oxygen.
- All you can conclude in fMRI is compare magnetic property (e.g. greater signal in area 1 vs. in area 2), without comparison to area 2, area 1 means nothing.
- Every experiment using fMRI, you must create base rate to compare magnetic activity.
- BOLD signal
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