Resting state EEG

Question 1

What is a dipole?

Answer 1

A small element of activity in the brain

Question 2

What does dipole fitting solve?

Answer 2

The inverse problem - where the signal is coming from

Question 3

How does dipole fitting work?

Answer 3

You estimate where you think the signal from your measured signal is coming from.
Often start with one dipole and the computer programme will generate the signal this dipole would create and see if this matched our measured signal
Adjust the position until we get the best fit

Question 4

What happens if we can’t find the ‘best fit’ from our dipole?

Answer 4

Increase the number of dipoles by 1

Question 5

What is the advantage of dipole fitting?

Answer 5

• Simple to calculate; modern computers do it instantly
• Can potentially model several simultaneous sources at once
• works well with simple sensory experiments

Question 6

What are the disadvantages of dipole fitting?

Answer 6

• Not good for more complicated experiments; more susceptible to noise
• Need to have a good guess at where the activity is coming from
• Need to know no. of dipole sources in advance

Question 7

What is a Distribution Current Model?

Answer 7

Try to work out a continuous distribution of current within the brain or a region which might be generating response
Assumes the weakest (lowest current) is the correct one

Question 8

What paradigm is Garrido et al use that involved a distribution current model? What psychiatric disorder gets affected by this?

Answer 8

Mis-match negativity = play a continuous tone but then throw in a ‘oddball tone’ that evokes a stronger response in the frontal and temporal lobe
Schziophrenia

Question 9

How does EEG fair compared to MEG in a distribution current model?

Answer 9

More distributed source ie not as good spatial res
But MEG might not be as good at finding the frontal sources

Question 10

What are the advantages to Current Density modelling?

Answer 10

Don’t have to guess how many sources or where
Can be used in complex experiments

Question 11

What are the disadvantages to current density modelling?

Answer 11

Computationally more demanding
Produces diffuse, weakly active sources that tend to be from surface of brain - hard to localise deep sources

Question 12

How can we solve the problem of localising deep sources?

Answer 12

fMRI/MRI

Question 13

How did dale et al (2000) use both fMRI and MEG to improve spatial localisation?

Answer 13

Had ptps do two language tasks in the MEG - hearing and repeating novel words and repeated words.
Use the Current Density model but source was widely spread
Did the same task in fMRI and combined with MEG on the computer to make a more precise and accurate model

Question 14

What does beamforming localise compared to the other two methods?

Answer 14

Localises oscillations and detects increases and decreases in power in frequency bands such as alpha or theta

Question 15

What’s the name for power increases or power decreases in the oscillatory bands?

Answer 15

Increases = Event-Related Syncronisation
Decreases = Event-Related Desyncronisation

Question 16

How did the results differ in Singh et al’s study when using MEG compared to fMRI on visual stimlus?

Answer 16

fMRI - showed a general increase in activity in the visual cortex
MEG - showed suppression of ALPHA and increase of GAMMA freq.

Question 17

What did Singh et al’s study tell us about the roles of the frequency bands?

Answer 17

GAMMA - processing the stimulus
ALPHA - visuo-spatial attention - coupling of info

Question 18

What results did the MEG show compared to fMRI on a motion perception stimulus? What kind of power did the MEG data show?

Answer 18

fMRI - general activation of motion and processing areas
MEG - Suppression of both ALPHA and BETA where fMRI showed activation
Event-related Desyncronisation

Question 19

What is the correlation found between MEG power and fMRI BOLD signal?

Answer 19

BOLD signal increases, low-freq power bands decrease and high-freq power bands increase

Question 20

Where has empirical evidence of changes in the suppressive network been found?

Answer 20

Epileptic patients - got them and healthy patients to listen to auditory track

Question 21

What is connectomics?

Answer 21

The mapping of structural and functional connectivity

Question 22

What did Friston et al find about connectivity in schizophrenia?

Answer 22

At multiple levels, theres a neurobiological deficit that results in disruption of connectivity

Question 23

What can the Default Mode Network tell us about performance?

Answer 23

People who turn of the DMN strongly do equally as well in the task as those that activate the parts of the brain required for the task strongly

Question 24

How was the link between DMN with those with Alzheimer and performance demonstrated in buckner et al’s study?

Answer 24

Those with Alzheimer’s show a failure to switch off the default mode network at the earlier stages where the hippocampus is yet to be affected

Question 25

What the advantages to resting state?

Answer 25

Easy to do - no task and good for removing task demands
Reveal fundamental neurophysiological mechanisms
Appear repeatable

Question 26

What are the disadvantages to resting state

Answer 26

Poorly controlled
Are coupled networks functionally relevant?
fMRI - slow haemodynamics (not direct measure) and other confounds such as drugs, breathing, fitness

Question 27

What approaches can you take when assessing resting state MEG

Answer 27

Activation vs connectivity from region to region
Which frequency
Amp-to-Amp vs amp phase vs phase coupling
within vs cross-freq
seed based or atlas based

Question 28

What does atlas-based analysis do?

Answer 28

Creates a network for each of the frequency bands for each different location/region

Question 29

Which frequency shows increased connectivity in those with brain injuries not shown on MRI?

Answer 29

Low frequency bands show increased connectivity

Question 30

Which frequency band was disrupted in schizophrenia

Answer 30

Gamma and Alpha

Question 31

What can resting state connectivity in MEG do compared to other techniques? What psychiatric disorder demonstrates this?

Answer 31

See how stable they are over time
Schizophrenia - connectivity states change