Biology - Lecture 2 (BOLD signal)

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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. 


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