Resting-state fMRI

Question 1

How do you do a resting-state fMRI scan?

Answer 1

• lie as still as possible (and look at a fixation cross –> not necessary, but helps not to fall asleep and to avoid eye wondering)

Question 2

What does resting-state fMRI do? What does it measure?

Answer 2

• resting brain consumes 20% of energy
• resting-state activity is not random: regions associated with the same function communicate with each other (showed similar activation patterns - connectivity)

Question 3

experiment resting-state fMRI

Answer 3

• Picture A shows activity during the task while Picture B shows activity during resting state; Region a and b are correlated.
• On the left you see activity during a motor task (contrast: tapping finger vs. Lying still). –> activity in motor cortex
• As a next step, they measured brain activity during resting state (b) and if they zoomed in on one region in the motor cortex (a) and observed which region’s activity correlated with activity within that region, a similar pattern of connectivity patterns was emerging.
• -> Thus, they saw that regions associated with motor processing (a) showed connectivity with the other motor processing region (b).
• On the graph on the right, you see high correlation between green and orange lines which depict motor activity on the right and left motorcortex: If activity in one of those regions increases, the same will be true for the other region.
• –> This is an example of how functional connectivity can be analysed during resting state.

Question 4

How is resting-state fMRI measured?

Answer 4

• brain activity is measured during resting-period
• measures how activity (=timeseries) of a region co-variate with another region
• represents functional architecture of the brain (you capture how the brain is organized functionally)

Question 5

How is resting-state fMRI analyzed?

Answer 5

• various analyses techniques:
  1. seed-based
  2. region-to-region
  3. whole-brain connectome

Question 6

seed-based analysis

Answer 6

correlation of one region (=seed) with rest of brain, e.g. amygdala=seed

Question 7

region-to-region analysis

Answer 7

• correlation of set of regions with set of regions
• regions with high correlation = networks
• connectivity within und between networks

Question 8

whole-brain connectome

Answer 8

• correlation of regions of whole brain to regions of whole brain
• RQ: How is the whole brain connected to the whole brain?
• regions are called nodes,
• connectivity between regions: edge
• -> you can calculate the within and between network connectivity or relate the network to certain functions

Question 9

Why do you do resting fMRI?

Answer 9

• resting-state connectivity relates to individual differences in (social) cognitive processes

Question 10

study example resting-state fMRI

Answer 10

• RQ: How connectivity worked between and within the default mode network (here shown in red) and the fronto-parietal network (shown in green) and the salience network (shown in blue) interact with each other to predict how well participants perform on a mentalizing task.
• mentalizing task: “Reading the mind in the eyes test” -
• Calculated connectivity within & between networks for each subject and predict the performance on mentalizing task
• -> Connectivity within and between networks explain individual differences in mentalizing: explains 28% of variation between individuals in mentalizing performance

Question 11

resting-state fMRI- related to psychopathology

Answer 11

• schizophrenia and psychotic disorders:
  1. structural and functional brain abnormalities
  2. positive and negative symptoms
  3. social dysfunction

Question 12

resting-state fMRI- related to psychopathology: experiment

Answer 12

• 28 patients at high risk or first episode & healthy controls
• RQ: Does the connectivity between those networks differ between pp with schizophrenia risk and healthy controls?
• No differences between pp with psychotic disorder and healthy controls
• BUT: Connectivity within networks explained severity of negative symptoms
• -> Lower connectivity within the default mode network together with higher connectivity between regions of the salience network could predict the severity of the negative symptoms.
• -> When the groups as a whole was investigated, no differences were found but when zooming in on the symptom severity, the connectivity on the resting brain contributed to these symptoms

Question 13

rsfMRI: Pros

Answer 13

• easy to measure

- everyone can do it (children, elderlies, disorders…: no differences in task performance)

Question 14

rs-fMRI: Cons

Answer 14

• fMRI signal not direct measure of neural activity
• effects of head motion on connectivity
• effects of physiology: cardiac pulsation in the brain and respiration –> measure motion and heart rate to control for it!

Question 15

functional connectivity definition

Answer 15

temporal dependence of neuronal activity patterns of anatomically separated brain regions

Question 16

What are resting-state networks?

Answer 16

• networks of anatomically separated brain regions that show a high level of functionally connectivity during rest
• around 8 identified, e.g., default mode network
• most of these resting-state networks tend to represent known functional networks, overlapping regions that are known to share a common function

Question 17

special characteristic of default mode network

Answer 17

• elevated level of neuronal activity during rest –> suggesting that activity of this network is reflecting a default state of neuronal activity of the human brain
• has been linked to core process of human cognition: integration of cognitive and emotional processing, monitoring the world around us, mind-wondering