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Neuroimaging > MEG/EEG > Flashcards

MEG/EEG Flashcards

1
Q

Delta; Frequency range and function

A

<4Hz
Sleep, suppression of irrelevant task information, disease marker

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2
Q

Theta: Frequency range and function

A

4-8Hz
Memory processing

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3
Q

Alpha: Frequency and function

A

8-12Hz
Attention and inhibitory control

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4
Q

Beta: Frequency and function

A

12-30Hz
Motor

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5
Q

Gamma: Frequency and function

A

28Hz+
Sensory/cognitive - passive viewing of high contrast stimuli

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6
Q

What does a MEG measure

A

The coordinated firing of the pyramidal cells and interneurons

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7
Q

How quick can MEG measure activity?

A

Every 1000th of a second

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8
Q

What kind of processing do high and low frequencies do?

A

High = local
low = across the brain

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9
Q

What are the oscillatory MEG markers of schizophrenia?

A

Reduced freq and amp of GAMMA bands
desyncronous oscillations = disconnectivity in the brain

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10
Q

Where do the neural signals arise from?

A

Grey matter

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11
Q

What are the 5 levels/techniques of electrical signals we can measure?

A
  1. Single electrode recording
  2. Multiple-unit recording
  3. Local field potential
  4. Electrocorticography
  5. EEG/MEG
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12
Q

What is an action potential?

A

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

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13
Q

Give an example of a single electrode recording study

A

Hubel and Weisel; measured single neurones of cats in the visual cortex
Found each neuron had an orientation

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14
Q

Give an example of a multi-unit recording study

A

Found a representation of a single neuron in quite high level concepts = jennifer anniston

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15
Q

What is the limitation about multi-unit recordings

A

Functionality isn’t just down to firing rate

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16
Q

How are local field potentials measured?

A

put electrode directly onto brain
filter out signal below 300Hz

17
Q

What kind of signal do local field potentials measure?

A

measure slower oscillations
bulk activity - not individual neurons
slower synchronised activity

18
Q

What does electrocorticography measure?

A

Activity leaked onto the surface of the brain

19
Q

What can EcoG be used for

A

Animal studies and localise areas of the cortex generating epileptic activity

20
Q

What is a current dipole and what is a cortical dipole

A

current - smallest possible element of current
cortical - mass coherent activity from many neurons and oriented perpendicularly to the cortical surface

21
Q

What is the reference problem

A

Where to put the reference electrode - it needs to be ‘silent’ but this is hard to do

22
Q

What are evoked potentials

A

electrical responses to a stimuli

23
Q

What did Tallon-Baudry discover when presenting ptps with real or illusory object or no object

A

Synchronised burst of 40Hz at Cz for real and illusory triangle but not for no object

24
Q

What are the issues with EEG

A

Susceptible to muscle artefacts

25
Q

What is the advantage to MEG compared to EEG

A

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

26
Q

How do we deal with the ‘noise’ that MEG is susceptible to?

A

Shielded room
Gradiometers; Specially wound-up coils that reject noise

27
Q

Explain a study where MEG has managed to measure subcortical signals

A

Theta from the hippocampus using spatial filtering = simulation of maze following showed enhanced theta oscillations

28
Q

Why do we want to monitor eye movements?

A

Ensure keeping eyes open - asleep?
Compliance with task
Control for exp confounds
Monitor muscle artefacts

29
Q

What two methods can monitor eye movements?

A

Eye tracking
Electrooculography (EOG) = direct recording of electrical signal from the eye

30
Q

Why mustn’t we do an MRI recording before MEG

A

Could magnetise any metal in the head such as fillings and corrupt the MEG signal

Neuroimaging (11 decks)

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