fMRI

Question 1

Structural Imaging

Answer 1

Based on the fact that different types of tissue (skull/ grey matter/ white matter) have different rates of absorption: used to construct a detailed map of brain structure
Computerised Tomography (CT)
● Creates image of the amount of x-ray absorbed by different tissue types Magnetic Resonance Imaging (MRI)
● Creates image of soft tissues in the body through disruption of the alignment of protons in the body and measurement of the subsequent change in magnetic field.

Question 2

Functional Imaging

Answer 2

Based on assumption that neural activity produces local physiological changes in that region of the brain. Used to produce dynamic maps of moment-to-moment brain activity during cognitive tasks.
● Brain doesn’t store oxygen, and only limited glucose: active areas get supplies from the blood. Therefore, activation of neurons = increased blood flow to that area.
● Baseline responses are always necessary because the measure is of relative activation
o Hemodynamic measures: indirect measures of neuronal activity through downstream
consequences of neural activity Positron Emission Tomography (PET)
● Radiolabelled pharmacological agents are used to trace certain specific pathways Functional Magnetic Resonance Imaging (fMRI)
● Uses standard MRI equipment, measures the distortion in local magnetic fields caused by conversion from oxyhaemoglobin to deoxyhaemoglobin

Question 3

Hemodynamic response function

Answer 3

Initial dip: as neurons consume oxygen, there is a rise in deoxyhaemoglobin amount, which translates as a dip in BOLD signal
2. Overcompensation: increased oxygen consumption means increased blood flow to the area. When blood flow is higher than consumption, the BOLD signal increases towards the plateau.

Question 4

MRI + BOLD = f MRI

Answer 4

B

Question 5

MRI + BOLD = f MRI

Answer 5

• poor temporal resolution –> Hemodynamic Response function peeks 6 seconds after the initial neural signal occured.
• Blood oxygen level dependent
• the contrast of oxygenated to deoxygenated hemoglobin is measured in order to specify which brain region.

–> This is how the activity of the brain is able to localise