Resting state EEG Flashcards
What is a dipole?
A small element of activity in the brain
What does dipole fitting solve?
The inverse problem - where the signal is coming from
How does dipole fitting work?
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
What happens if we can’t find the ‘best fit’ from our dipole?
Increase the number of dipoles by 1
What is the advantage of dipole fitting?
- Simple to calculate; modern computers do it instantly
- Can potentially model several simultaneous sources at once
- works well with simple sensory experiments
What are the disadvantages of dipole fitting?
- 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
What is a Distribution Current Model?
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
What paradigm is Garrido et al use that involved a distribution current model? What psychiatric disorder gets affected by this?
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
How does EEG fair compared to MEG in a distribution current model?
More distributed source ie not as good spatial res
But MEG might not be as good at finding the frontal sources
What are the advantages to Current Density modelling?
Don’t have to guess how many sources or where
Can be used in complex experiments
What are the disadvantages to current density modelling?
Computationally more demanding
Produces diffuse, weakly active sources that tend to be from surface of brain - hard to localise deep sources
How can we solve the problem of localising deep sources?
fMRI/MRI
How did dale et al (2000) use both fMRI and MEG to improve spatial localisation?
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
What does beamforming localise compared to the other two methods?
Localises oscillations and detects increases and decreases in power in frequency bands such as alpha or theta
What’s the name for power increases or power decreases in the oscillatory bands?
Increases = Event-Related Syncronisation
Decreases = Event-Related Desyncronisation
How did the results differ in Singh et al’s study when using MEG compared to fMRI on visual stimlus?
fMRI - showed a general increase in activity in the visual cortex
MEG - showed suppression of ALPHA and increase of GAMMA freq.
What did Singh et al’s study tell us about the roles of the frequency bands?
GAMMA - processing the stimulus
ALPHA - visuo-spatial attention - coupling of info
What results did the MEG show compared to fMRI on a motion perception stimulus? What kind of power did the MEG data show?
fMRI - general activation of motion and processing areas
MEG - Suppression of both ALPHA and BETA where fMRI showed activation
Event-related Desyncronisation
What is the correlation found between MEG power and fMRI BOLD signal?
BOLD signal increases, low-freq power bands decrease and high-freq power bands increase
Where has empirical evidence of changes in the suppressive network been found?
Epileptic patients - got them and healthy patients to listen to auditory track
What is connectomics?
The mapping of structural and functional connectivity
What did Friston et al find about connectivity in schizophrenia?
At multiple levels, theres a neurobiological deficit that results in disruption of connectivity
What can the Default Mode Network tell us about performance?
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
How was the link between DMN with those with Alzheimer and performance demonstrated in buckner et al’s study?
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
What the advantages to resting state?
Easy to do - no task and good for removing task demands
Reveal fundamental neurophysiological mechanisms
Appear repeatable
What are the disadvantages to resting state
Poorly controlled
Are coupled networks functionally relevant?
fMRI - slow haemodynamics (not direct measure) and other confounds such as drugs, breathing, fitness
What approaches can you take when assessing resting state MEG
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
What does atlas-based analysis do?
Creates a network for each of the frequency bands for each different location/region
Which frequency shows increased connectivity in those with brain injuries not shown on MRI?
Low frequency bands show increased connectivity
Which frequency band was disrupted in schizophrenia
Gamma and Alpha
What can resting state connectivity in MEG do compared to other techniques? What psychiatric disorder demonstrates this?
See how stable they are over time
Schizophrenia - connectivity states change
