fMRI: methods / W4L2 Flashcards
What are activation “blobs”?
What to activation colours represent?
The are statistical effects in experiment, often colour coded. Red for ‘activation’, and blue for ‘deactivation’.
Can you compare activation of brain regions? Why or why not.
You cannot compare the reaction of different brain regions because each region has a different hemodynamic response function.
What is a HRF?
A hemodynamic response functionis a physiological response. When a specific area of the brain becomes active, it requires more oxygen and nutrients to support the increased metabolic demand.
What is the timeline of HRF?
Peak onset 4-8sec. Approx.16 seconds return to baseline.
What is adenosine triphosphate (ATP)?
This is the primary engergy currency in cells. ATP is produced by metabolishing glucose. This process requries oxygen that can be measured with fMRI scanners.
How does fMRI measure neural activity?
fMRI does NOT measure neural activty directly. Rather, it is indirect measure described as hemodynamic neuroimaging method.
Why is oxygenated blood useful?
Oxygenated blood is diamagnetic, meaning it has a magnetic quality which enhances our signal
What is the difference between oxygenated and deoxygenated blood?
What is neural activity accompanied by?
Oxygenated (Hb):
Diamagentic
Enhance Signal
Deoxygenated (dHb)
Paramagnetic: Distortions/artefacts
Decrease Signal
Neural Activity = Need glucose = Local oversupply in oxygenated blood = Better BOLD
Does fMRI looking at action potentials?
No. fMRI reflects signal differences due to different oxygen levels
In a typical fMRI experiment, how do we get BOLD?
- While participants engage in a cognitive task
- Repeated measurements to reduce noise
- Differences in BOLD tell us whether a brain region ‘is engaged’ in a task
Can you compare activity in the same brain region?
Yes. While you can’t compare across different brain regions. You can compare imaging with the same brain region
Same HRF
What do we use to map areas of enhanced activity into the structural image of the brain?
Statistical Parametric Mapping.
A General Linear Model is fitted to brain activity at each measurement point/voxel (50,000-100,000x)
(i.e. fit model to explain the data. how well does the model explain the data. Similar to a t-test)
Significantly stronger activation in region X for task A compared to task B is interpreted as involvement of the region X in task A
What can we gather from a single brain signal?
Nothing. Brain activity must be measured repeatedly and then averaged across many trials. This is because the signal is noisy.
