How is fMRI a functional imaging technique?
It tells us which brain areas are active during a task
How does fMRI work?
It measures the level of oxygenated blood and deoxygenated blood
- if a brain area is active, it required more oxygenated blood
- once the brain region uses the oxygen, the blood becomes deoxygenated
- this deoxygenated blood distorts the magnetic signal; but oxygenated blood receives a good magnetic signal
What is attenuation?
The reduction of a signal
- the more dense, the more attenuation
- the less dense, the less attenuation
What is a hemodynamic response?
The time it takes the brain to ask for oxygenated blood and use it
What is the time frequency of fMRIs?
the hemodynamic response time is between 8-10 seconds long, so we are not able to quickly compare signals
What is a voxel?
A 3D pixel (like minecraft)
What is the most critical step when an fMRI experiment is going to be run?
The selection of the baseline task (you have to start with the brain’s most basic function, i.e. just not doing anything, then get participant to fixate on a cross, then look at faces, etc)
What is fMRI multivoxel pattern analysis (MVPA)?
- it provides info about a pattern of activity but also patterns across brain regions
- each category of an object is associated with a unique pattern of activation (ex. furniture vs. faces vs. animals)
- the algorithm sets a boundary of prediction between the two variables
What kind of category seems to be important to the brain?
Semantic categories
What do fMRI resting state approaches focus on?
They examine patterns of brain activity in the absence of a task
What is default mode network?
The pattern of brain activation when brain is at rest
- this varies with different pathologies like Alzheimer’s
What are the advantages of doing fMRI resting state approaches?
- it doesn’t require a degree of cognitive ability in the participant
- only a short session is required (10-15 mins)
What are the advantages of using fMRI?
- it is a functional technique
- high spatial resolution
- higher temporal resolution than PET
- non-invasive
- patterns of activity
What are the disadvantages of using fMRI?
- expensive
- claustrophobic
- noisy
- poor temporal resolution compared to EEG and ERP
- identifies multiple brain regions
- it is an indirect measure of brain activity
What brain area seems to be responsible for language switching?
The caudate nucleus
What is an ERP?
It is an event related potential (the action potential from a stimulus)
What does EEG measure?
The neural activity of thousands of neurons
Describe ERPs?
- ERPs must be averaged
- they are negative and postitve
What is P300 associated with?
ERP pattern when higher order processes are involved
What is associated with N400?
ERP associated with semantic processing (400-600ms)
- semantic relationship: does the word fit? if it doesn’t, this spike is higher
What are the advantages of ERP?
- direct measurement of mass neuronal activity
- high temporal resolution
- non-invasive
What are the disadvantages of ERP?
poor spatial resolution
