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BOLD fMRI

BOLD fMRI. What is fMRI ?. fMRI stands for Functional MRI Functional MRI measures a physiological process in real time; it looks at the function rather than the structure. What is BOLD fMRI ?. BOLD stands for Blood Oxygen Level Dependent

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BOLD fMRI

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  1. BOLD fMRI

  2. What is fMRI? • fMRI stands for Functional MRI • Functional MRI measures a physiological process in real time; it looks at the function rather than the structure

  3. What is BOLD fMRI? • BOLD stands for Blood Oxygen Level Dependent • BOLD fMRI measures brain activity by measuring blood oxygen level • When an area of the brain is more active, it calls for more blood flow to supply glucose and oxygen

  4. How does it work? • Hemodynamic response MRI Signal Neuron Time Blood vessel Ratio of O2 to no O2 = 10:4 Red Blood Cell (without O2) Red Blood Cell (with O2)

  5. How does it work? • Hemodynamic response Neuron Activates MRI Signal I NEED FOOD!!!! Time Blood vessel Ratio of O2 to no O2 = 7:7 Red Blood Cell (without O2) Red Blood Cell (with O2)

  6. How does it work? • Hemodynamic response MRI Signal That’s better! Time Blood vessel dilates Ratio of O2 to no O2 = 21:7 More blood flow

  7. How does it work? • Hemodynamic response Neuron rests MRI Signal I’m good now! Time Blood vessel returns to normal Blood vessel Ratio of O2 to no O2 = 10:4

  8. Hemodynamic Response, Step by Step • Brain Activates and begins to use more glucose and oxygen • Brain calls for more glucose and oxygen • Blood vessels dilate to increase blood flow • Brain deactivates • Blood vessel returns to normal

  9. Back to BOLD • So, our signal increases when blood flow increases • And we know that blood flow increases when brain activity increases • Therefore, we can measure brain activity by looking at our BOLD fMRI signal

  10. HOWEVER: • The brain is never completely inactive, and we always have blood flow • We also don’t know what a “normal” level of blood flow is from person to person, so we don’t know what a “normal” signal level is • Let’s call our MRI signal our dependent variable since that’s what we’re really measuring, and we know that it represents blood flow. So what do we need now?

  11. CONTROL! • We need to know what the signal looks like when we are sure that the part of the brain we’re looking at is not activated • Let’s look at how we design a BOLD fMRI experiment

  12. Experiment Design • Let’s say we want to look at motor activation

  13. Experiment Design • If blood is always flowing through the brain, how can we design our experiment?

  14. Block Design Active Active Active Active Rest Rest Rest Rest

  15. Block Design • So we subtract the signal during rest blocks from the signal during active blocks • If there is a significant difference, then we conclude that the brain is activating as a result of our activity • We can then divide the brain into a grid to see exactly where the activation is taking place

  16. Results

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