Resting State

Question 1

1. What are resting-state networks? How are they defined? Difference between definition of DMN and other RSNs

Answer 1

Resting activity = Spontaneous activity not attributable to specific inputs ( intrinsically originated)
RSNs= Anatomically separated regions that are functionally connected during rest, i.e. that show synchronous neural activity

In contrast to other networks, DMN is “task negative”  negatively correlated with arousal and effort, and with areas involved with demanding cognitive tasks

Question 2

2. Difference between ROI and ICA methods, advantages and disadvantages of both methods.

Answer 2

Regions of interest
• Based on hypotheses
• You choose a seed region and analyse correlations to other regions
• Pro: Interpretation is relatively easy
• Con: risk of missing information, higher risk of signal contamination

Independent component analysis
• Not based on particular hypotheses
• Statistical analysis to disentangle fMRI signal into independent components (i.e. components of activity that don’t share variance)
• Pro: exploratory, less sensitive to contamination
• Con: interpretation is more difficult

Both lead to comparable results in a number of studies. Best to combine both approaches!

Question 3

3. Major Resting state networks.

Answer 3

Default Mode Network
• Precuneus/Posterior cingulate, lateral parietal area, medial prefrontal cortex

Sensorimotor network
• Pre- and postcentral gyrus, SMA
• Anatomical and functional correspondence with sensorimotor functions
o Overlap with sensorimotor areas, lateralisation corresponds to that during active tasks

Visual network(s)
• Up to three distinct components, covering striate and extrastriate regions
• Influenced by a visual task performed beforehand

Executive control network
• Medial frontal gyrus, superior frontal gyrus, ACC
• Strength of intrinsic connectivity correlates with performance on trail-making test

Lateralised fronto-parietal networks
• Inferior frontal gyrus, medial frontal gyrus, precuneus, inferior parietal cortex, angular gyrus
• Associated with several functions (memory, language, attention, visual, motor)
• Specifically affected by prior sensorimotor learning

Auditory network
• Superior temporal gyrus, Heschl’s gyri, Insula, Postcentral gyrus
• Only anatomical correspondence with auditory areas

Temporo-parietal network
• Inferior frontal gyrus, medial and superior temporal gyrus, angular gyrus
• Regions typically associated with language processing

Question 4

4. What are the possible functions of DMN?

Answer 4

• Spontaneous cognitive processes (mind-wandering)
• Introspective processes and awareness (self-reflective thinking, thinking about past and future)
• Facilitating/monitoring performance of active tasks
o DMN connectivity positively correlates with WM performance
• Intrinsic properties of the brain
o DMN is active during sleep and anesthesia
• Memory?
o Hippocampus might be part of the DMN

Question 5

5. Clinical applications of RSNs. Promises and pitfalls.

Answer 5

Promises
• Especially interesting to study differences between patients and controls
• Can work with uncooperative subjects

Alzheimer’s
• Patients show impaired FC in both hippocampi
o Less so but still pathological in MCI
• Patients show reduced functional connectivity in the DMN (PCC and hippocampus)
• ApoEe4 allele: increase in DMN FC

schizophrenia
• Idea: Schizophrenia symptoms could arise from an overactive DMN
• However: inconsistent findings so far

Presurgical planning
• First evidence for precision in localising functional areas
• Studies with more patients and more areas/functions needed

Disorders of consciousness
• Current diagnosis based on behaviour, quite inaccurate
• Resting state imaging can help in diagnosis and prognosis
o Intensity of DMN connectivity was shown to correlate with level of consciousness
o Peak significance: Precuneus

So far, literature focuses exclusively on the DMN – what about the other networks?