lecture 2 - experiments

Question 1

ways to measure behavior and physiological signals in fMRI

Answer 1

1. button boxes & joysticks: basic behavioral responses
2. eye tracking: gaze behavior & pupil size
3. microphones: speech
4. pneumograph belts: breathing
5. pulse oximeter: blood oxygenation, heart rate
6. experimental considerations such as video games

Question 2

ways to present stimuli

Answer 2

1. screen + mirror: standard setup for visual stimuli
2. goggles & headphones: 3D stimuli, virtual reality, sounds, narratives, music, etc.
3. vibration devices: tactile stimuli, touch
4. galvanic stimulator: vestibular stimuli, perceived movement
5. gustometers & odor stimulators: taste, smells, flavors
6. brain stimulation: magnetic or electrical stimulation

Question 3

experimental control (task-based paradigms)

Answer 3

1. constrained & artificial conditions
2. clear result interpretation, but requires many controls
3. many feasible experiments and analyses
4. easier to standardize and replicate
5. analysis assumptions are met through task design
6. results might not generalize
7. full control of behavior not feasible/desirable for understanding the brain

Question 4

naturalistic conditions (task-based paradigms)

Answer 4

1. closer to real life (ecological validity) with better generalizability of results
2. interactions between factors can be studied
3. discovery of unexpected phenomena more likely
4. focus on measuring rather than controlling behavior
   -> when you give up control, you need to measure more
5. result interpretation more difficult than experimental control
6. invited unconstrained data exploration
7. analytical challenges such as collinearity and missing data
8. MRI experiments limited in terms of naturalism

Question 5

different experimental philosophies of task-based paradigms

Answer 5

experimental control and naturalistic conditions: most studies are not one or the other.

the research question determines how much experimental control is optimal.

Question 6

eye tracking in fMRI

Answer 6

1. viewing behavior
2. is important even in passive tasks: eye movements predict brain activity while people rest

Question 7

resting state (rs-FMRI)

Answer 7

used to study brain function and connectivity without the need for specific tasks or stimuli -> brain activity during rest

typical experiment: lie in the scanner and fixate at a dot (or close your eyes)

Question 8

seed-based functional connectivity (rs-fMRI)

Answer 8

revealing functionally connected regions

take the signal of one ‘seed’ voxel or region and correlate with one or all other voxels. The resulting connectivity maps can reveal which regions of the brain are functionally connected with the seed region

Question 9

Parcellation based on brain-wide “connectivity fingerprints” (rs-fMRI)

Answer 9

grouping voxels with similar connectivity to the rest of the brain
-> Each region has a unique “connectivity fingerprint”

Question 10

network-level perspective on mental processes (rs-fMRI)

Answer 10

comparing connectivity estimates across conditions (e.g., eyes open vs eyes closed)

Question 11

why study rest (rs-fMRI)

Answer 11

1. easy to perform (e.g., no task equipment required)
2. widely applicable in special populations (e.g., patient groups, elderly, children)
3. task-evoked responses often explain shockingly little variance (<5% of total signal)
4. fertile ground for the development of data-driven analysis tools

Question 12

rs-fMRI common criticism

Answer 12

1. no control or measurement of what participants experience
2. often difficult interpretation of results
3. resting state results are not very predictive of behavior
4. imaging artifacts (e.g., caused by motion) strongly affect connectivity results
   -> can significantly distort fMRI connectivity results because they introduce spurious changes in signal that can be mistakenly interpreted as neural activity or connectivity.
5. functional connectivity does not reflect anatomical connectivity
   -> i.e., does not measure the strength of communication between two regions

Question 13

task-based approaches vs resting state approaches

Answer 13

task-based approaches offer control and better interpretability

resting-state approaches can be great for data driven exploration (or integrated paradigms)

Question 14

behavioral tracking (e.g., eye tracking)

Answer 14

can help interpret data acquired under any and all tasks
-> i.e., resting state and task-based paradigms

Question 15

advantages of task-based paradigms compared to resting state

Answer 15

better control over participant’s experience

Question 16

advantages of naturalistic paradigms compared to tightly controlled ones

Answer 16

1. interactions between experimental components can be studied more easily
2. results are more likely to generalize to other tasks

Question 17

what is the default mode network

Answer 17

brain regions with stronger activity during rest than during tasks

Question 18

inter-subject correlations

Answer 18

quantifies signal covariations between voxels of different participants

Question 19

double dissociation

Answer 19

• activity A > B in one area, B > A in another
• implies separate processes in A and B
• not strong evidence

Question 20

separate modifiability

Answer 20

• A but NOT B in one area, B but NOT A in another
• implies truly separate processes

Question 21

parametric modulation

Answer 21

• manipulate (or measure) variables in a parametric fashion within-person
• can provide stronger evidence than contrasts for brain-task/brain-performance relationships
• performance-related effects within subjects

Question 22

multiple subtraction designs

Answer 22

experimental approach where the effects of several different conditions are individually subtracted from a control condition to isolate specific cognitive or neural processes