Functional magnetic resonance imaging (fMRI) extends structural MRI to investigate changes associated with brain activity. This lesson introduces the BOLD signal and the physiological link between neuronal activity and blood flow.
MRI uses a strong magnetic field to align the spins of nuclei in the body. Gradient magnetic fields allow the scanner to distinguish locations, and radiofrequency (RF) pulses alter the spins. As the nuclei return toward equilibrium, their emitted energy is detected and used to form an image. Structural MRI primarily depicts anatomy.
All flashcards
Why is the BOLD signal an indirect measure of brain activity?
It reflects vascular changes associated with neural activity rather than directly recording neuronal electrical signals.
What is the typical timing of the hemodynamic response to a brief event?
It begins after a delay, peaks about 4–6 seconds later, and then declines.
What is the main spatial-resolution trade-off of using smaller fMRI voxels?
They can localize activity more precisely but usually contain less signal and may lower signal-to-noise ratio.
What is reverse inference in fMRI?
Inferring that a particular mental process occurred because a brain region associated with it is active.
Why can a lesion complicate clinical interpretation of BOLD fMRI?
It can alter blood flow independently of neural activity and thereby obscure the BOLD response.
Quiz questions
In fMRI, what does the repetition time (TR) specify, and what does it not overcome?Answer: It sets how often volumes are sampled, but it does not remove the delay caused by the vascular response.
How does a general linear model commonly analyze fMRI data?Answer: It relates a voxel's time series to predicted condition responses specified in a design matrix.
What distinguishes multi-voxel pattern analysis (MVPA) from a typical voxel-wise GLM?Answer: MVPA uses patterns across multiple voxels to classify or predict conditions, often testing on independent data.
Which comparison best describes the complementary strengths of EEG and fMRI?Answer: EEG has high temporal resolution, while fMRI generally provides better spatial localization but slower responses.
What does vascular-space occupancy (VASO) measure, and how does it obtain contrast?Answer: It measures cerebral blood-volume changes by suppressing the blood signal.