fMRI Flashcards
Give three reasons why fMRI is well suited for studying the neural underpinnings of human behaviour.
It is non-invasive.
It can measure brain function over short periods of time to capture dynamic aspects of mental processes and behaviour.
It measure activity across the whole brain simultaneously to see how multiple brain regions interact to mediate complex behaviours.
Describe in one sentence how fMRI works.
It tracks brain function based on changes in local blood oxygen levels that occur in response to neural activity.
fMRI uses the magnetic properties of which atom and why?
Hydrogen atoms because they are the dominant source of protons in the body.
Protons intrinsically rotate around an axis. What does this give them?
Angular momentum and a magnetic dipole along the axis.
What is the direction of the dipole under normal conditions?
It is random for different protons.
Describe longitudinal magnetisation.
When placed in a strong external magnetic field, a subset of protons align with the direction of this field. The number of protons that align is proportional to the field strength.
What is the purpose of transmitting a radiofrequency (RF) pulse?
To measure the composition of tissue based on the aligned protons.
What happens to the protons when a radiofrequency (RF) pulse is transmitted?
It induces a weaker magnetic field perpendicular to the strong field.
This misaligns the protons with the strong field, which now acts as a torque, causing the proton spin axes to precess in an arc on the transverse plane.
What happens to protons that are tilted heavily into the transverse plane when a coil is placed nearby?
The spinning magnet induces a current in the wire that reverses as the poles alternate.
What is the function of the receiver head coil in an MRI machine?
It measures alternating current induced by protons precessing synchronously. Amount of current = concentration of precessing protons.
Describe longitudinal relaxation with time constant T1.
The spin orientation of protons gradually relaxes back to the direction of the strong magnetic field, causing them to precess less in the transverse plane and thus generate less signal.
Describe transverse relaxation with time constant T2.
This is a second type of decay that occurs while protons are still precessing in the transverse plane. Local interaction with other atoms causes some protons to precess faster or slower. Since they get increasingly out of sync, the induced current alternates less reliably and signal is lost.
What is the strength of the magnetic field in most modern MRI machines?
3T (Tesla).
What is the advantage of using a higher field strength, e.g. 7T?
Higher resolution imaging of cortical layers.
Which part of the MRI machine is called the bore?
The tunnel-like outside.
How is behaviour measured when a participant completes an experimental task in an MRI machine?
Manual responses with a button box and/or eye movements with an eye tracker.
