fMRI Flashcards
fMRI directly measures…
A: Neural events
B: Deoxygenated blood flow, correlated with neural activity
C: Oxygenated blood flow, correlated with neural activity
D: Oxygenated haemoglobin, correlated with neural activity
B: Deoxygenated blood flow, correlated with neural activity
Which statement is false?
A: deoxygenated haemoglobin is
less sensitive (or paramagnetic) than oxygenated haemoglobin
B: When the oxygen is absorbed during neural activity,
the haemoglobin becomes deoxygenated
C: deoxygenated haemoglobin is
more sensitive (or paramagnetic) than oxygenated haemoglobin
D: fMRI measures the ratio of the two types of haemoglobin
A: deoxygenated haemoglobin is
less sensitive (or paramagnetic) than oxygenated haemoglobin
is FALSE.
fMRI results are reported as the difference in ratio of ____
oxygenated and deoxgenated haemoglobin
As a brain areas become active, the amount of blood being directed to the area ___
increases
Although neural events occur at the ____ level, blood flow changes occur much more ____
millisecond; slowly
Initial rise in blood flow may not be evident for several seconds and can peak __-__ seconds after event of interest
6-10
Increase in oxygenated blood can represent a signal
change of as much as __, although typically around __
5%; 1%
Because fMRI is ___, it can be used repeatedly within or across sessions with the same individual
non-invasive
___ resolution is superior to all other brain imaging methods (e.g., better than PET, EEG, MEG), resolving activity estimates down to levels across the whole-brain of as little as ___
Spatial; 1mm3
While signal changes associated with a particular cognitive operation (or event) must be repeated for ___ ___,
you can discriminate brain-wide activity for a series of ___ events
signal averaging; different
fMRI provides you the ___ ___ to compare events based upon a subject’s performance
post-hoc flexibility
Wagner et al. found that encoding-related activity could be seen in ___ and ___ regions
prefrontal regions (e.g., left inferior frontal gyrus) and hippocampal regions
In Wagner et al.’s wordlist memory task, no difference between remembered vs. forgotten words was seen in lower-level perceptual regions (e.g., visual cortex), indicating that ___
while the words were viewed equally well, they were not remembered
equally well
The standard contrast map in most fMRI studies identifies ___ that correlate with a experimental manipulation, but we still need to infer an area’s ____ contribution
regions of difference; functional
True or false? fMRI is good at determining how brain activity (or changes therein) in one location is related to
another
FALSE. New analysis techniques are being developed to examine
‘connectivity’, with much interesting findings, but all currently lack the ability to determine relative timing and direction.
We still can’t tell which region activates another
fMRI has __ temporal resolution.
poor
Voodoo correlations: Vul et al. 2009 identified that many papers in social neuroscience suffer from ___. They find high correlations .7-.9 between BOLD activity and ___.
non-independence errors; measures of personality traits or self-reported scales.
The strength of these correlations was questioned because they are greater than the reliability of the underlying measures
The voodoo correlations problem is caused by…
- Researchers initially identifying ROIs associated with a particular event (social distress) and a self-reported scale
- Then work out the average correlation coefficient for
individuals in only those regions - Biases analysis to regions where the correlation is likely
to be highest
Vul et al. identified the voodoo correlations problem in __% of the papers they surveyed.
54%
Bennett et al. 2009 scanned a dead salmon during a picture viewing MRI study.
Using a standard parametric analysis, they identified ___
significant BOLD activity in voxels in the brain of the dead salmon
Bennett et al.’s (2009) dead salmon problem is caused by:
Multiple comparisons.
- fMRI analysis involves comparing activity in two states (active vs rest) across each voxel in the brain
- There are over 40,000 voxels in a typical brain scan
- 40,000 comparisons completed with an alpha level of P >.05 will find 5% of voxels statistically active by chance
Bennett et al.’s (2009) dead salmon problem highlights the need for ___
replication
In __ images, artefacts, or loss of fMRI signal, occurs near junctions between ____, for example, around the sinuses, ear canals.
Makes it particular difficult to acquire reliable BOLD activity from regions
such as ____
T2; air and tissue; orbitofrontal cortex and subcortical regions
List 5 fMRI design types.
- Block Design
- Slow ER Design
- Rapid Counterbalanced ER Design
- Rapid Jittered ER Design
- Mixed Design
Subtraction designs are…
basic contrasts between task and control, or one type of task and another
Issues with subtraction analyses
- Can have multiple comparisons/baselines
- Most common baseline = rest
- In some fields the baseline may be straightforward. For example, in vision studies, the baseline is often fixation on a point on an otherwise blank screen
- Be careful that you don’t try to subtract too much
- What are people really doing during rest?
Problems with a rest baseline?
- For some tasks (e.g., memory studies), rest is a poor, uncontrolled baseline — memory structures (e.g., medial temporal lobes) may
be DEactivated in a task compared to rest - To get a non-memory baseline, some memory researchers put a low-memory task in the
baseline condition — e.g., hearing numbers and
categorizing them as even or odd
5 advantages of event-related design?
1) Flexibility and randomization
- eliminate predictability of block designs
- avoid practice effects
2) Post hoc sorting (e.g., correct vs. incorrect, aware vs. unaware, remembered vs. forgotten items, fast vs. slow RTs)
3) Can look at novelty and priming
4) Rare or unpredictable events can be measured, e.g., P300
5) Can look at temporal dynamics of response
- Dissociation of motion artefacts from activation
- Dissociate components of delay tasks
- Mental chronometry
Effect of adding trials: Averaging BOLD signal from an increasing larger
number of trials (from 4 to
144) results in…
a significant linear increase in the spatial extent of
statistical significant activity
fMRI interaction problem: researchers claiming that __.
The presence of activity in one group vs the absence of it in another group does not tell you __.
one effect is larger than the other without testing them directly or performing an interaction analysis;
that there’s a difference between those groups if you don’t do an interaction analysis.
BOLD overlap and jittering:
Closely-spaced haemodynamic impulses __.
Constant ITI causes problems.
Varying the timing of events allows you to __
summate;
separate, or deconvolve, the signal specific to a particular type of event.
