8 Neurohemodynamic coupling
What’s happening in the brain when neural states change, and why do we care so much about blood flow?
In a later chapter (fMRI contrast) we’ll get into more detail about alternatives to BOLD contrast, but this chapter is about tried and true Blood Oxygenation Level-Dependent (BOLD) fMRI. Functional hyperemia.
First, to get our bearings, some brain geometry and guidelines for resolution of a “typical” fMRI experiment.
And now, the goods. What is neural activity? How is vascular structured? How is blood flow regulated? How do neurons ask for more blood flow? What does that do to our image contrast?
Bonus material for folks who love physics details — simulations of how veins perturb the magnetic field, and how that depends on size and orientation.
Exercises
- Does fMRI directly measure neural activity?
- Does fMRI directly measure oxygen consumption?
- Does fMRI directly measure blood flow?
- What does a positive signal change during an fMRI experiment mean?