...Chapter 2: Methods ptII Flashcards
What is diffusion tensor imaging? What is it measuring?
DTI, this is a scan to see white matter. Water moves in the brain, n extracellular space it doesn’t have a direction (isotropic), but in micro.t axons it does (anisotropic). FA measure degree of anisotropy n each voxel, higher FA=stronger flow. Then tractography can piece together these to see where white matter tracts go.
What is the difference between voxels that have high or low fractional anisotropy?
High FA means a stronger directional flow of water, Low FA is a weaker directional flow of water. More structured movements means higher FA
What is tractography?
tractography is the ability to piece together the directionality of finer tracts, then use algorithms to piece together major nerve finer tacts. Can see where white matter tracts actually go.
How does PET work? What is the subtraction method?
PET scans, you inject a radio isomer into the bloodstream then you get the person to think so that the areas that are used have more blood in them. The isotope then decays (ir releases a positron which runs into electrons which relate gamma rays which then hit the detectors 180degrees apart). Dif isotopes are used for different senarios/brain areas. Using the subtractive method which is experiment condition minus the ctrl (all areas are the same except for one) to get the activation difference you can see which area actually react. Takes a long time to scan, uses an isoptoe, cant use women/kids, can only see changes not absolute activity
What is the BOLD response?
Bold oxygenation level dependent effect, this is the changes in magnetic resonance due to brain areas replacing their deoxygenated blood with oxygenated blood. (active area need new oxygenated blood). Bold effects can be time-locked to specific events, so we know that performing a certain task causes BOLD responses to occur (cause the changes are small)
What neuroimaging method has the best spatial resolution? The best temporal resolution?
EEG and fMRI the best?? MRI has best spacial resulution, EEG good for temporal imaging MEG is good and fast (in milliseconds)
You should know that EEGs (and ERPs) reflect dendritic field potentials.
Pick up the signal released by dendritic field potentials (when dendrites are excited or inhibited).
What is the difference between an EEG and an ERP?
Egg is just the measuring of activity at dendrites, a continuous measure of brain activity. Event related potentials is when you do an even (stimulus) then measure activity right after that (which area produce the most activity? can look at changes at every millisecond interval)
What are alpha, beta, gamma, theta, delta, and high gamma waves? You don’t need to know their frequencies, but you should know how they are different.
The band have different frequencies with delta the lowest frequency (longer wavelengths deep sleep) and gamma being the highest frequency (short wavelengths, excited)
What is Talairach space? What is this important?
Talairach space is a brain atlas used to coridinate and map brain stuctures. This is important because everyone has a different shaped and sized brain so this allows us to shirk and stretch a person brain to fit a template so it’s easier to compare and understand which regions are which.
What is the difference between a ‘run’ and a ‘session’ in fMRI studies?
session (all of the scans collected from one subject in one day). Run (one continuous period of fMRI scanning usually 5-7min)
Why should you put all conditions in the same fMRI run?
Cause you don’t want people sitting in the machine for hours on end it’s hard to stay still that long so the shorter the time the better, plus its really pricey so best to not.
Describe 3 types of fMRI study designs. What are advantages and disadvantages of each.
Bock design (a bunch of one type then rest then a bunch of another type. High detection power and accurate representation of hemodynamic response not as important here. But can get subkecys into mental set ,can’t look at single events ). Slow Event Realated (type 1 wait type two wait. allows you to look at individual trials and discard ons of person moved. But subjects an get bored and there’s poor detection power). Rapid Event Jittered Related (mix up the amount of time in-between trials which allows the computer to pick up on individual trials. Good for post hoc sorting [orrect vs. incorrect] and decent ability to detect effects. But complex anaylsis)
If you were performing a rapid event-related fMRI study, why would you jitter the intertrial interval?
With jittering, the scanner will measure the hemodynamic function at different points. Lets the computer ‘fill in the gaps’ better than if the function were always measuring at the exact same place. Can see individual trials and distinguish between post hoc sorting
What is the default mode network? How does it differ from the salience network?
Default mode: lost in your thoughts (self reflective thinking). The salience network is a collection of regions of the brain that select which stimuli are deserving of our attention
