8. Default Mode Network & Resting State Flashcards
What is referred to as “resting state”?
- A state where we are not actively engaging in a task
- Is often a paradigm on its own (fixation cross, eyes open/closed)
- resting conditions are known as baseline*
What does functional connectivity mean?
Looking at the correlation of changes in activity across different regions in the brain
- What areas work together?
- Can be investigated using seed-based Functional Connectivity analysis (in fMRI) where you choose an area (seed) to later correlate with other areas.
Biswal et al (1995):
Functional connectivity in the brain
Bilateral finger tapping in a scanner
- allowed them to identify what regions were active during tapping
Then got the time-series data of one of the active regions from that condition (Left motor cortex) and correlated it with the rest of the brain
- the right motor cortex activity was correlated
- There were some regions which reduced in activity during resting state condition
Default mode of brain function:
Shulman et al (1997)
- PET & fMRI (finger tapping/rest)
rest||finger tap||rest||finger tap…
- Engaging in the active task was found to coincide with deactivations in some brain regions
Raichle et al (2001):
Showed the evidence of Default brain activity
- Showed evidence for a baseline state in the human brain (0 set point as they called it) and named it the ‘Default Mode of Brain Function’ which is suspended during specific goal directed behaviours
- there was actual decrease in the default mode network (not return to baseline) when engaging in behaviours
- Upholding the Default Mode during goal directed behaviour had a substantial energy demand
Emergence of the default mode network
Grecius et al (2003):
Found that the Default Mode Network consisted of:
- Posterior Cingulate Cortex
- Ventromedial Cortex
Also analysed data from some visual processing task…
- Found that connectivity remained the same during the task
!!!!!Thus the default mode network remains intact and active during both rest and task states
Seed Based analysis is driven by…
hypothesis
- method involves selecting a region based on hypothesis and finding out which other areas’ activity correlates with it
Independent component analysis and default mode network
Beckmann et al (2005):
ICA is a data-driven approach, no apriori hypothesis required…
- Looking at time-series data of the brain and breaking it down into individual components (seeing what different areas are active)
!!!They found that there is more resting state networks existing along with the Default Mode Network
Fox et al (2005):
Interactions of resting state brain networks
Dorsal Attention network:
- regions routinely exhibiting task related activation
Default Mode Network
- regions routinely exhibiting task related deactivation
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There is an ANTI-correlation between the two
Alterations of resting state networks in mental health disorders
Buckner et al (2005):
DMN and Alzheimer’s
- the regions showing high amyloid deposition in adults with Alzheimer’s highly resemble the regions showing default activity in young adults
Alterations of resting state networks in mental health disorders
Christakou et al (2013):
DMN, ADHD & Autism
- Measures of Precuneus (Key region of DMN) BOLD response
- There is a significant delay in activity in the ADHD and autism groups compared to controls
Alterations of resting state networks in mental health disorders
Whitfield-Gabriell (2009):
- Schizophrenia
Greicius et al (2007):
- Depression
- DMN regions activity is altered in Schizophrenia and Depression compared to controls
Smith et al (2009)
- Ran Independent Component Analysis (ICA) for 36 subjects at rest and found a bunch of networks
- then they looked at thousands of activation studies (Using neurosynth.org) involving nearly 30k subjects who performed a task and ran ICA on them
They demonstrated that we can get the same results by running ICA analysis on 36 subjects at rest and 30k subjects undergoing a task
- shows that the full repertoire of active networks is present both at rest and during tasks
