MEG and Cognitive Experiments

Question 1

What can MEG/EEG be used to measure

Answer 1

Oscillations at rest or during a task

Question 2

How are oscillations useful?

Answer 2

Can be biomarkers for individual variability in health and disease

Question 3

What frequency increases in activity in the primary visual cortex and was is suppressed in the presentation of simple visual stimulus?

Answer 3

Gamma increased
Alpha and beta suppressed

Question 4

In what other animals can you observe the pattern of oscillations in the primary visual cortex when presented with a visual stimulus

Answer 4

Cats and monkeys

Question 5

Why is it important to have these resting state oscillation patterns?

Answer 5

Use them as a reference if we look at oscillations with those on certain drugs or with certain diseases

Question 6

Is gamma in V1 a useful measure of individual variability? What range of variability has been shown?

Answer 6

Yes, they do vary from person to person but are stable
30-70Hz

Question 7

What relationship was shown between gamma frequency and age as shown by Bompas et al?

Answer 7

Gamma freq decreases with age
Seperate study - 13y/o had freq 55-60 and 70 y/o 40Hz

Question 8

What did van pelt demonstrate about genetics and gamma frequencies in their twin study?

Answer 8

Gamma freq was identical in monozygotic twins but different for dizygotic twins although they still had a stronger relationship than unrelated pairs

Question 9

How is the oscillation caused?

Answer 9

Inhibitory inter-neurons inhibit the action of the pyramidal cells that are excitatory

Question 10

How does this oscillation change? What is the Gamma freq dependent on?

Answer 10

Changes in circuit due to lack of either cells or disrupted connection
Dependent on AMPA (excitatory) and GABA (inhibitory) ratio

Question 11

How does the E/I balance relate to the neuropathophysiology of schizophrenia?

Answer 11

SCZ has be theorised to be due to a disruption of the following:
GABA
Glutamate (Excitation)
Inflammation (e.g microglial)

Question 12

What did Shaw et al’s study show about Gamma oscillations and SCZ?

Answer 12

Both amp and freq was reduced in those with SCZ
Computational model showed it was related to reductions in inhibiton

Question 13

What might be more important than spatial location, magnitude and frequency of oscillations when using MEG?

Answer 13

Ability to modulate connectivity b/ween brain areas dynamically in order to perform tasks

Question 14

What do some propose about gamma oscillations in the visual cortex?

Answer 14

They are the mechanism by which information is transmitted between brain regions

Question 15

How did Pascal Fries try to explain this communication within the visual cortex in gamma oscillations

Answer 15

Said that when gamma oscillations from two neurones come into phase and become synchronised it means they are communicating with each other

Question 16

How did Jensen and Mazaheri explain this communication?

Answer 16

Can control by changing the amount of alpha in those regions
Alpha = switching off alpha

Question 17

What example of a study supported the explanation that alpha frequencies modulated communication in the brain?

Answer 17

Had people read whilst in the MEG
Found synchronisation of the Alpha band to be predominantly in the left hemisphere - where the language network usually is

Question 18

How were oscillations connected to parkinson’s disease patients?

Answer 18

The frequency of the patients hand tremor had a strong phase coherence with the frequencies in certain parts of the brain - in particular the motor cortex that isn’t found in healthy controls

Question 19

Define attention

Answer 19

The process of enhancing processing in the presence of distractors

Question 20

What is Bottom-Up processing in regard to attention?

Answer 20

Stimulus driven, automatic process
e.g cocktail party scenario
pre-attentive processing

Question 21

What is Top-down processing in regard to attention

Answer 21

Hierarchical system. (directing attention) High level cortical regions exert a modulatory influence on lower sensory/motor systems

Question 22

What did a fMRI study show about shifting attention and activation in the visual cortex?

Answer 22

When shifting attention but not gaze, the visual cortex is activated in the same way as if it were activated by a stimulus in that location
Other regions also showed a negative BOLD response

Question 23

What happens in the alpha response when doing a posner cueing paradigm with EEG - Worden et al

Answer 23

When attending to the left, alpha power is reduced on the right side of brain and vise versa = lateralised response

Question 24

What is a limitation of Worden et al’s EEG study with posner cueing paradigm?

Answer 24

Not good spatial localisation

Question 25

What did Siegel et al find about spatial localisation during a cueing paradigm?

Answer 25

Activation in the posterior ((larger supression in Alpha/Beta and then large gamma response) - sensor space

Question 26

What happens with the gamma band in siegel et al’s study?

Answer 26

Also have lateralisation of the gamma band to the side you’re attending to

Question 27

So what is the advantage to using MEG rather than fMRI for these attention paradigms?

Answer 27

MEG can go deeper into the changes in frequency rather than just bulk changes in activity

Question 28

Why is MEG better at measuring the effects of drugs than fMRI

Answer 28

fMRI is affected by neurovascular coupling so drugs could change the BOLD response indirectly though vascular changes
I.e harder to control

Question 29

Why is MEG better at measuring the effects of drugs than EEG? How was this proven?

Answer 29

EEG is more susceptible to muscle movements
When using a neurotoxin that paralysed the face, a lot of the high frequencies went down proving there to be a lot of muscle contamination

Question 30

What happened when giving ptps benzos?

Answer 30

Increase in BETA oscillations over the motor cortex
Alpha not changed

Question 31

What is the benefit with using MEG in drug studies?

Answer 31

Able to see the pharmacodynamic profile of the drug i.e how long it takes to kick in, how long it lasts, when it peaks and does it work

Question 32

What did Hall et al’s study tell us about the pharmacodynamic profile of benzos?

Answer 32

Increased beta over motor cortex
Started seeing increase around 10-20 minutes in, peaked at 20-30 minutes and then was mostly back to normal by 60 mins

Question 33

What effects has alcohol been found to have in MEG studies on the visual and motor cortex?

Answer 33

Effects the GABA inhibitory system (boosts)
Increased gamma amp but reduced freq

Question 34

What have MEG studies shown about the effects of ketamine?

Answer 34

Affects the NMDA receptor system = Leads to disinhibition or neuronal circuitry = hallucinatory and sedative effects
Boosts theta, suppresses alpha and beta in posterior, enhances low and high gamma

Question 35

What is the effect on attention in the brain when given a drug that affects the cholinergic system? Bauer et al

Answer 35

Same as before; suppressed in side attending and enhanced in side not attention BUT this was ENHANCED by the drug

Question 36

What does Bauer et al’s study mean clinically?

Answer 36

Could be used to treating Alzheimers which is thought to affect the cholinergic system