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 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

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

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

How does it work? Hemodynamic response MRI SignalTime Blood vessel dilates Ratio of O2 to no O2 = 21:7 More blood flow Thats better!

How does it work? Hemodynamic response Blood vessel MRI SignalTime Ratio of O2 to no O2 = 10:4 Blood vessel returns to normal Neuron rests Im good now!

Hemodynamic Response, Step by Step 1.Brain Activates and begins to use more glucose and oxygen 2.Brain calls for more glucose and oxygen 3.Blood vessels dilate to increase blood flow 4.Brain deactivates 5.Blood vessel returns to normal

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

HOWEVER: The brain is never completely inactive, and we always have blood flow We also dont know what a normal level of blood flow is from person to person, so we dont know what a normal signal level is Lets call our MRI signal our dependent variable since thats what were really measuring, and we know that it represents blood flow. So what do we need now?

CONTROL! We need to know what the signal looks like when we are sure that the part of the brain were looking at is not activated Lets look at how we design a BOLD fMRI experiment

Experiment Design Lets say we want to look at motor activation

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

Block Design Active Rest Active Rest

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

Results