BOLD

Question 1

Is oxygenated haemoglobin diamagnetic or paramagnetic?

Answer 1

Diamagnetic

Question 2

Three relaxation effects, what is T1 measuring?

Answer 2

slow recovery of longitudinal magnetization
due to spin-lattice interactions

Question 3

What is relaxation time T2 measuring?

Answer 3

Fast dephasing of spins due to spin-spin interactions

Question 4

What is relaxation time T2* measuring?

Answer 4

Fast dephasing of spins due to combination of
spin-spin interactions and
magnetic field inhomogeneities
This is what is influenced by BOLD effect

Question 5

What happens if you have less deoxygenated haemoglobin? Does the signal decay faster or slower?

Answer 5

The magnet is stronger, the signal decays faster (it dephases faster) and it is weaker, opposite for oxygenated.

Question 6

What does the BOLD signal originate from? What role does neuro-vascular coupling have in this?

Answer 6

The BOLD signal originates from the afflux of highly oxygenated blood in the site of neural activation due to neuro-vascular coupling, hydrogen spin relaxation gets slower, T2* gets higher

Question 7

What are the initial dip and the undershoot indicating on a level of blood composition?

Answer 7

There is more deoxygenate blood

Question 8

What is the time course for canonical HRF?

Answer 8

Initial dip (0-2s), overshoot (rise, peak ~4-6s, decay),
undershoot (~10-20s). Typical length: ~20-30s

Question 9

Cheng et al, Neuron, 2001, what did it show?

Answer 9

That Ocular Dominance Columns (and probably other brain structures) could be mapped, this implies a resolution of around 1mm

Question 10

Temporal precision
Duration

Question 11

Temporal precision
Onset latencies

Question 12

Variability of HRF

Answer 12

HRF is variable between different subjects
No correlation between peak latency and amplitude

Question 13

What does BOLD measure at the activity level (improve)

Answer 13

BOLD measures changes in post synaptic potentials