Lecture 3 - Flashcards
What does ERP stand for?
Event related potential, spikes in electrical activity due to a stimulus or task
What’s on the x axis of a EEG? What do large deflections sometimes mean?
Time
Can sometimes mean muscle movement or contraction
What is the N170?
Negative deflection at 170ms after the stimulus has been presented - signalling that the brain is processing
What does TMS stand for ?
Trans cranial magnetic stimulation
How does TMS work? What does it create?
You place the device over a certain population of neurons and then at a certain level of stimulation then the neurons fire until they short circuit and can’t fire anymore.
Creating a virtual lesions
Lasts about 15 minutes
What is the down side of TMS?
You can only lesion the outer surfaces not the deep structures
When they used to do TMS what did they use instead of magnetic pulses?
Electric pulses which are much more dangerous
What does PET stand for ? How does it work?
Positron emission tomography
Inject a radioactive tracer into the blood, different tissues have different metabolic rates so take In the compound at different rates, this is detected by the scanner and recorded.
What does the red on PET scan mean?
The redder the spot the more metabolic Activity therefore the more blood and more tracer.
Why is MRI better than PET ?
Doesn’t use a radioactive isotope as a tracer
How does a MRI work?
Magnetic fields align the protons in the brain
Short radio pulses are added which mess with the alignment
It takes time for the protons to realign
Different tissues take different amounts of time to realign
What are the two categories to evaluate the scanners abilities on?
Spatial resolution
Temporal resolution
How does increasing the tesla of the Magnetic effect an MRI ? What’s the highest tesla we use at the moment?
Increasing the tesla means a better spatial resolution
9 tesla
What is resolution measured in?
In MRI what are the White areas, grey areas and black areas?
Voxels
White - White matter
Grey - grey matter
Black - ventricles
What are the three types of MRI?
Structural (T1 weighted)
Measures the amount of time for protons to realign
Best resolution 1mm
Diffusion weighted
Measures the water diffusion through the brain
Middle resolution 2mm
Functional (T2* weighted)
Signal loss due to blood oxygen levels
Poorest resolution 3mm
What does DTI stand for? What does it measure?
Diffusion tensor imaging
Measures the diffusion of water in a given direction, water can’t pass through the fatty layers of myelin sheaths so if water isn’t there you can assume it is White matter.
So you can work out the White matter tracts
How do you quantify what you find using DTI?
Fractional anisotropy
Low FA value of 0.2 would suggest a poorly constructed myelin sheath so water can travel in any direction
High FA of 0.8 would mean that the water can only go in one direction and the sheaths are well constructed.
Does every brain have tracts in the same place?
No there are inter brain differences, so some have tracts in slightly differently places, but they tend to all be relatively similar.
How does fMRI work?
There is neuronal firing in a part of the brain
This signals neuro vascular systems, signals the brain to send oxygen rich blood to this area to keep the metabolic rate going.
Blood then flows to this area with lots of oxygen
The scanner picks this up and it is known as the BOLD response
What does the scanner actually measure? The amount of blood ?
No the scanner measures the magnetic signals in the blood. So oxygenated blood isn’t magnetic whereas deoxygenated blood is magnetic, the scanner picks up blood going from oxygenated to deoxygenated. Deoxygenated disrupts the magnetic field .
What do we call the BOLD response over time?
What does the curve look like?
Haemodynamic response function
Function peaks about 6-8 seconds after the onset of the stimulus (poor temporal resolution ) because blood has to flow to the area and actually be used.
Surely there is blood all over the brain, how do we know what is responsible for what?
There is preferential activation, so the whole brain is doing things and using up oxygen but certain areas respond more to certain stimuli.
What’s the most effective way of using scanning technology if they all seem to have problems ?
Combine different methods, for example use fMRI to localise an area responsible for something and then use DTI to see if the two areas are connected at all. (Kim & Kim 2005)
What does EEG measure?
The electrical activity in the brain measured using electrodes placed on the scalp, so electrical activity in the brain creates voltage change on the scalp
Represents the summed IPSPs and EPSPs of neurons around the electrode
