Lecture 27B Flashcards
(42 cards)
Describe the spatial and temporal resolution in different imaging techniques
EEG: very good temporal resolution, bad spatial resolution
MEG: good spatial resolution and temporal resolution
MRI/fMRI: very good spatial resolution and bad temporal resolution
What are the strength and weaknesses of MRI?
Strengths:
- It is non-invasive
- excellent anatomical detail due to good spatial resolution
- can be any anatomical plane
- very good at distinguishing between different tissue types
Weakness:
- poor temporal resolution
What does MRI reveal and how is it interpreted?
- MRI reveals the brain structure and it can be interpreted by visual inspection (radiology) or quantitatively
What is a deformation matrix used for
it is used to make inferences of neuroanatomy and diseased states
What is DTI?
DTI –> diffusion tensor imaging
- DTI is a type of MRI that helps us see white matter tracks to analyze the structural connectivity in the brain
How does DTI work?
- it works by measuring water molecule diffusion along axons in white matter (they move along axons because they are restricted by the myelin).
- it tracks water movement at each voxel and assigns it a tensor to describe the direction and strength of water diffusion
What is DTI tactography
- it uses DTI data to map white matter pathways in the brain
What does fMRI measure and how?
- fMRI measured blood oxygen dependent signal
(NOT neural activity) - when brain is activated, energy gets used up because cells start firing, driving metabolic demand
- when this happens the brain will regulate by rushing more oxygenated blood into the parts of brain consuming the most energy (this is the BOLD signal)
- this is then picked up by the fMRI scan
When could we use DTI
- we could use DTI, by looking at a group of kids with autism and another group without and see if white matter tracts are developing normally or abnormally
what are the different types of MRI
- DTI
- fMRI
When could we use fMRI?
- we could use it to see if motor cortex activation is different in people with Parkinson’s than people of same age, sex and absence of neurological disorders
Describe BOLD response curve
- neurons start working and using up blood thats initially there
- blood rushes in
- overshoot where brain rushes O2 rich blood to areas that need it most
- neuron activity continues (positive BOLD response)
- neuronal activity goes down
- blood gets used up
- things go back to normal
Describe an fMRI experimental design
- BLOCK design
- because fMRI has poor temporal resolution you’ll have patient do condition 1 (smiling) in long blocks, then condition 2 in long blocks
- you’ll then look at your region of interest where your getting your a clear BOLD signal, making it easier to see brain activation
Why don’t we use short blocks in the fMRI experimental design
- short block length can limit return to baseline hemodynamics response function
- this blurs the fMRI signal and makes it hard to tell apart the different response to different conditions
Why do we use long block in fMRI experimental design
- long blocks maximize difference in signal between conditions
What is the area of the brain called that is deactivated across many tasks?
- default mode network (DMN)
When does DMN activate
- when you are not doing a task like resting or day dreaming, but other “resting-sate networks” are also seen in spontaneous correlations
What does fNIRS stand for
functional near-infrared spectroscopy
What does fNIRS do
- it measures BOLD
What are the advantages and disadvantages of fNIRS
Advantage:
- cheap and portable
Disadvantages:
- does not get deep structures
- poor spatial and temporal resolution
How does fNIRS work?
- fNIRS shines light though the skull and measures BOLD
When would you use fNIRS
when you need something cheap and portable
What does PET measure
It measures regional metabolism to map function such as metabolism at dopamine binding sites
What does PET measure
- it measures brain activity based on metabolism and can map where activation is happening at dopamine receptors
