MEG and Cognitive Experiments Flashcards
What can MEG/EEG be used to measure
Oscillations at rest or during a task
How are oscillations useful?
Can be biomarkers for individual variability in health and disease
What frequency increases in activity in the primary visual cortex and was is suppressed in the presentation of simple visual stimulus?
Gamma increased
Alpha and beta suppressed
In what other animals can you observe the pattern of oscillations in the primary visual cortex when presented with a visual stimulus
Cats and monkeys
Why is it important to have these resting state oscillation patterns?
Use them as a reference if we look at oscillations with those on certain drugs or with certain diseases
Is gamma in V1 a useful measure of individual variability? What range of variability has been shown?
Yes, they do vary from person to person but are stable
30-70Hz
What relationship was shown between gamma frequency and age as shown by Bompas et al?
Gamma freq decreases with age
Seperate study - 13y/o had freq 55-60 and 70 y/o 40Hz
What did van pelt demonstrate about genetics and gamma frequencies in their twin study?
Gamma freq was identical in monozygotic twins but different for dizygotic twins although they still had a stronger relationship than unrelated pairs
How is the oscillation caused?
Inhibitory inter-neurons inhibit the action of the pyramidal cells that are excitatory
How does this oscillation change? What is the Gamma freq dependent on?
Changes in circuit due to lack of either cells or disrupted connection
Dependent on AMPA (excitatory) and GABA (inhibitory) ratio
How does the E/I balance relate to the neuropathophysiology of schizophrenia?
SCZ has be theorised to be due to a disruption of the following:
GABA
Glutamate (Excitation)
Inflammation (e.g microglial)
What did Shaw et al’s study show about Gamma oscillations and SCZ?
Both amp and freq was reduced in those with SCZ
Computational model showed it was related to reductions in inhibiton
What might be more important than spatial location, magnitude and frequency of oscillations when using MEG?
Ability to modulate connectivity b/ween brain areas dynamically in order to perform tasks
What do some propose about gamma oscillations in the visual cortex?
They are the mechanism by which information is transmitted between brain regions
How did Pascal Fries try to explain this communication within the visual cortex in gamma oscillations
Said that when gamma oscillations from two neurones come into phase and become synchronised it means they are communicating with each other
How did Jensen and Mazaheri explain this communication?
Can control by changing the amount of alpha in those regions
Alpha = switching off alpha
What example of a study supported the explanation that alpha frequencies modulated communication in the brain?
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
How were oscillations connected to parkinson’s disease patients?
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
Define attention
The process of enhancing processing in the presence of distractors
What is Bottom-Up processing in regard to attention?
Stimulus driven, automatic process
e.g cocktail party scenario
pre-attentive processing
What is Top-down processing in regard to attention
Hierarchical system. (directing attention) High level cortical regions exert a modulatory influence on lower sensory/motor systems
What did a fMRI study show about shifting attention and activation in the visual cortex?
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
What happens in the alpha response when doing a posner cueing paradigm with EEG - Worden et al
When attending to the left, alpha power is reduced on the right side of brain and vise versa = lateralised response
What is a limitation of Worden et al’s EEG study with posner cueing paradigm?
Not good spatial localisation
What did Siegel et al find about spatial localisation during a cueing paradigm?
Activation in the posterior ((larger supression in Alpha/Beta and then large gamma response) - sensor space
What happens with the gamma band in siegel et al’s study?
Also have lateralisation of the gamma band to the side you’re attending to
So what is the advantage to using MEG rather than fMRI for these attention paradigms?
MEG can go deeper into the changes in frequency rather than just bulk changes in activity
Why is MEG better at measuring the effects of drugs than fMRI
fMRI is affected by neurovascular coupling so drugs could change the BOLD response indirectly though vascular changes
I.e harder to control
Why is MEG better at measuring the effects of drugs than EEG? How was this proven?
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
What happened when giving ptps benzos?
Increase in BETA oscillations over the motor cortex
Alpha not changed
What is the benefit with using MEG in drug studies?
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
What did Hall et al’s study tell us about the pharmacodynamic profile of benzos?
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
What effects has alcohol been found to have in MEG studies on the visual and motor cortex?
Effects the GABA inhibitory system (boosts)
Increased gamma amp but reduced freq
What have MEG studies shown about the effects of ketamine?
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
What is the effect on attention in the brain when given a drug that affects the cholinergic system? Bauer et al
Same as before; suppressed in side attending and enhanced in side not attention BUT this was ENHANCED by the drug
What does Bauer et al’s study mean clinically?
Could be used to treating Alzheimers which is thought to affect the cholinergic system
