MEG/EEG Flashcards
Delta; Frequency range and function
<4Hz
Sleep, suppression of irrelevant task information, disease marker
Theta: Frequency range and function
4-8Hz
Memory processing
Alpha: Frequency and function
8-12Hz
Attention and inhibitory control
Beta: Frequency and function
12-30Hz
Motor
Gamma: Frequency and function
28Hz+
Sensory/cognitive - passive viewing of high contrast stimuli
What does a MEG measure
The coordinated firing of the pyramidal cells and interneurons
How quick can MEG measure activity?
Every 1000th of a second
What kind of processing do high and low frequencies do?
High = local
low = across the brain
What are the oscillatory MEG markers of schizophrenia?
Reduced freq and amp of GAMMA bands
desyncronous oscillations = disconnectivity in the brain
Where do the neural signals arise from?
Grey matter
What are the 5 levels/techniques of electrical signals we can measure?
- Single electrode recording
- Multiple-unit recording
- Local field potential
- Electrocorticography
- EEG/MEG
What is an action potential?
All excitatory inputs are added and any inhibitory inputs are subtracted to give overall input activation
If its above the threshold, will send a train of action potential
Give an example of a single electrode recording study
Hubel and Weisel; measured single neurones of cats in the visual cortex
Found each neuron had an orientation
Give an example of a multi-unit recording study
Found a representation of a single neuron in quite high level concepts = jennifer anniston
What is the limitation about multi-unit recordings
Functionality isn’t just down to firing rate
How are local field potentials measured?
put electrode directly onto brain
filter out signal below 300Hz
What kind of signal do local field potentials measure?
measure slower oscillations
bulk activity - not individual neurons
slower synchronised activity
What does electrocorticography measure?
Activity leaked onto the surface of the brain
What can EcoG be used for
Animal studies and localise areas of the cortex generating epileptic activity
What is a current dipole and what is a cortical dipole
current - smallest possible element of current
cortical - mass coherent activity from many neurons and oriented perpendicularly to the cortical surface
What is the reference problem
Where to put the reference electrode - it needs to be ‘silent’ but this is hard to do
What are evoked potentials
electrical responses to a stimuli
What did Tallon-Baudry discover when presenting ptps with real or illusory object or no object
Synchronised burst of 40Hz at Cz for real and illusory triangle but not for no object
What are the issues with EEG
Susceptible to muscle artefacts
What is the advantage to MEG compared to EEG
Magnetic field comes exclusively from the area we are interested in as secondary magnetic fields from the primary current dipole cancel out - don’t have to worry about the conductivity of the head
Good temporal resolution
Rapid measurements
How do we deal with the ‘noise’ that MEG is susceptible to?
Shielded room
Gradiometers; Specially wound-up coils that reject noise
Explain a study where MEG has managed to measure subcortical signals
Theta from the hippocampus using spatial filtering = simulation of maze following showed enhanced theta oscillations
Why do we want to monitor eye movements?
Ensure keeping eyes open - asleep?
Compliance with task
Control for exp confounds
Monitor muscle artefacts
What two methods can monitor eye movements?
Eye tracking
Electrooculography (EOG) = direct recording of electrical signal from the eye
Why mustn’t we do an MRI recording before MEG
Could magnetise any metal in the head such as fillings and corrupt the MEG signal
