Functional Magnetic Resonance Imaging (fMRI): Basics

This set of flashcards covers the fundamental principles of Functional Magnetic Resonance Imaging (fMRI) as presented in the PSYC20006 Biological Psychology lecture, including physics, BOLD signal dynamics, and data interpretation.

According to the lecture recap, what is the primary origin of M/EEG activity?

M/EEG activity originates mostly from post-synaptic potentials.

Which brain sources are MEG and EEG respectively more sensitive to?

MEG is more sensitive to tangential sources, while EEG is more sensitive to radial sources (though it can also pick up tangential sources).

What is the primary difference between structural MRI (T1) and functional MRI (T2*) in terms of what they measure?

Structural MRI measures anatomy/structure, whereas functional MRI measures brain function/activity.

What substances or equipment are necessary to obtain superconductance in an MRI scanner?

A large superconducting electromagnet cooled by liquid helium is required.

What are the common magnetic field strengths used for experimental research and clinical purposes respectively?

Experimental research usually uses $3\,T$ (with some at $7\,T$), while clinical purposes typically use $1.5\,T$.

What are gradient coils used for in an MRI scanner?

They are used to modify the magnetic field for short periods of time to distinguish signals across space, such as different slices of the brain.

What is the Time to Repeat (TR) in the context of fMRI scanning?

The TR is the time it takes for a whole 3D volume of the brain to be scanned, typically taking about $1-3\,\text{seconds}$.

Define Echo Time (TE) in fMRI.

Echo Time is the interval between the excitation (RF pulse) and data acquisition.

What is the typical voxel size for a structural MRI versus an fMRI?

Structural MRI typically uses $1\,mm^3$ voxels, while fMRI typically uses $3\,mm^3$ voxels.

What does the Blood Oxygenation Level Dependent (BOLD) contrast measure?

It measures the ratio of oxygenated to deoxygenated hemoglobin in the blood.

Despite accounting for only $2\%$ of body weight, how much of the total body energy does the brain consume?

About $20\%$

In the BOLD signal phases, what causes the "initial dip"?

Oxygen is extracted from the blood, leading to a relative increase in deoxyhemoglobin and a decrease in the BOLD signal.

When does the Hemodynamic Response Function (HRF) peak typically occur?

$4-8\,\text{seconds}$ after stimulus onset.

How long does it take for the BOLD signal to return to baseline levels after neural activity?

Up to $16\,\text{seconds}$.

What is the typical magnitude of the BOLD signal change?

$$0.1-5\%$$

What specific type of neural activity does the BOLD signal correlate best with?

Local field potentials (LFPs), which reflect synaptic input rather than action potential output (neural firing).

What do the colored blobs in fMRI maps represent?

Coloured blobs are thresholded statistical maps (showing t-values) where activity in condition A is significantly different from condition B, not raw blood flow.

What is the "reverse inference" trap in fMRI research?

The trap of inferring a specific cognitive process solely based on the observed activity of a brain region, given that the same region may have multiple functions.