W1L1 - fMRI

Question 1

What are the 2 ways neuron activity can be measured

Answer 1

1. ) Directly - Electrical changes at the level of single neurons
2. ) Indirectly - Metabolic changes (Cognitive processes = ATP = Changes in blood flow/oxygenation)

Question 2

What is the function of fMRI. Is there a relationship between psychological states and __________ activity?

Answer 2

Localized hemodynamic changes from neural activity.

Often a relationship between psychological
states/performance measures and hemodynamic changes

Question 3

Why is fMRI popular, contrast with other methods

Answer 3

1. ) Non-Invasive (No needles, unlike PET)
2. ) Enable human studies
3. ) Focal (High precision, unlike EEG)

Question 4

What is the most widely used hemodynamic index

Answer 4

Blood Oxgenation Dependent Level (BOLD) signal

Question 5

What is the physics behind the basic MRI

Answer 5

Hydrogen has a single proton with random spin around axis.

When there is a radio pulse, it aligns parallel/anti-parallel and it spins back

Question 6

Cognitive processes require energy. Where do we get energy and how does it relate to fMRI

Answer 6

Need to produce ATP > Use oxygen from hemoglobin for energy.

fMRI relies on difference between magnetic responses between oxygenated and deoxygenated blood.

Question 7

Oxygenated vs Deoxygenated Blood. Difference in MRI signal

Answer 7

Oxygenated:
1.) Diamagnetic > No Distort

Deoxygenated:
1.) Paramagnetic > Distory

(Seiji Ogawa: Blood vessels more visible as Oxygen decreases)

Question 8

What is the Standard practice in analysis of BOLD. Why?

Answer 8

Spatial smoothing by 8mm to allow for group averaging by correspondence across brains

Question 9

How do we quantify BOLD changes

Answer 9

General linear model:

Correlate time course of the
BOLD signal change in each voxel of the
smoothed images with the measure of
cognitive function.

Question 10

What is the implication of the BOLD response (thus far)

Answer 10

Cortical Segregation/Modularity

Explains spatial structure of brain responses

Question 11

What are the purported neural correlates of BOLD. In the past and recently (Amptitude)

Answer 11

Amplitude of the BOLD signal associated with

1. ) local field potential (Large no. of active neurons)
2. ) increases in gamma-band electrical (EEG)
3. ) quite often correlated with spike frequency (Animal Studies)

Recent spatial localization of BOLD signal has been
associated with
- electrocorticographic (ECoG) at mm accuracy

Question 12

What are the 6 limitations of fMRI

Answer 12

1. ) Mislocalisation
2. ) Slow Changes
3. ) Uncertainity
4. ) Causality
5. ) Spatial Limitations (Localising and Resolving)

Question 13

1.) Mislocalisation of hemodynamics

Answer 13

Local changes in oxygen use and blood volume are carried downstream

Question 14

2.) Slow changes in hemodynamics

Answer 14

Disallow precise neural coupling

Question 15

3.) Uncertainty of the type of neurons involved

Answer 15

Excitation or Inhibitory unclear

Question 16

4.) Causation between 2 coactive areas

Answer 16

Correlation only

Question 17

5.) Spatial limitations on localising function activity

Answer 17

Vague despite being much better than EEG. Cannot explain layer-dependent activity

Question 18

6.) Spatial limitations on resolving functional activity

Answer 18

Spares Encoding (No): Population Encoding (Yes)
A BOLD signal driven by a stimulus does not mean that the entire area is used to process that stimulus, or even that class of stimuli

Question 19

What are the 2 fundamental limitation of fMRI

Answer 19

1. ) Some nerual activity (Magnetic Field) are too small to be localized with fMRI
2. ) Conclusions are ambiguous because it could reflect (blood velocity? volume? oxygen?)

Question 20

What are recent advances in fMRI

Answer 20

1. ) Multivoxel pattern analysis: More complex models (whole brain view) > Voxel encoding & Population field mapping: Better view of functional property of neurons
2. ) Hi Resolution (7T) Scanning: Isolate activity in single cortical column

Question 21

What are recent advances in structural MRI

Answer 21

1. ) New methods such as CBV Changes allows analysis of neural activity at the resolution of the cortical layer
2. ) Diffusion fMRI: Connectivity between brain regions (Map of how different brain regions are associated and correlated with one another)