Transcript UM-everywhere&#169

Journal club 6 Feb. ’09
Default mode network as revealed with
multiple methods for resting-state
functional MRI analysis
Long et al., J. Neurosci. Meth. 171 (2008) p.349-55
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Abstract
• Recently, human brain activity during a resting-state has attracted
increasing attention. Several studies have found that there are two
networks: the default mode network and its anti-correlation
network. Some studies have subsequently showed that the functions
of brain areas within the default mode network are crucial in human
mental activity. To further discern the brain default mode network as
well as its anti-correlation network during resting-state, we used
three methods to analyze resting-state functional magnetic
resonance imaging (fMRI) data; regional homogeneity analysis,
linear correlation and independent component analysis, on four
groups of dataset. Our results showed the existence of these two
networks prominently and consistently during a resting- and
conscious-state across the three methods. This consistency was
exhibited in four independent groups of normal adults. Moreover,
the current results provided evidences that the brain areas within
the two anti-correlated networks are highly integrated at both the
intra- and inter-regional level.
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Materials & Methods
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4 sites with different scanners (Siemens/GE; 1.5-3.0T)
4 x 10 healthy controls, matched across sites
170 2-s EPI volumes, 3.4 mm in plane, 4-7 mm slices
Pre-processing: slice timing, realignment, normalization,
resampling, temporal filtering (0.01-0.08 Hz), drift removal
• Analyses
• Regional homogeneity analysis (ReHo)
local signal coherence
• Functional connectivity analysis (SCA)
long-range area-related coherence
• Group independent component analysis (ICA)
integrated network coherence
• Conjunction analysis
combination
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ReHo
• Take time courses si(tj) in a
3x3x3 voxel neighborhood
• For each time course,
KCC
determine rank orders ri(tj)
• Calculate mean R(tj) over
all time courses
• Calculate measure of
deviation from expectation
2
J  1


 R(t j )  2 
KCC
j 1 J
• Kendall’s coefficient of
concordance
2
J  1


 R(t j )  2 
j 1 J
KCC 
; 0  KCC  1
2
1
12 J  J  1
180
2.5
180
2.5
2
160
2
160
1.5
140
1.5
140
1
120
1
120
0.5
100
0
80
-0.5
60
= 0.015
0
80
-0.5
60
-1
40
-1
40
-1.5
20
-2
0
-2.5
-1.5
20
-2
0
-2.5
0
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100
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180
2.5
180
2.5
2
160
2
160
1.5
140
1.5
140
1
120
1
120
0.5
100
0
80
-0.5
60
= 0.432
-0.5
60
-1
40
-1.5
20
-2
0
-2.5
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150
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350
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KCC = 0.983
0
80
-1
40
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0
0.5
100
-1.5
20
-2
0
-2.5
0
KCC = 0.324
0.5
100
0
50
100
150
200
250
300
300
350
350
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ReHo
• Individual smoothed KCC maps were divided by global mean
• Group level one-tailed t-test to determine KCC > 1.0 (Pcorr < 0.05)
A: posterior cingulate cortex
Group I
B: medial prefrontal cortex
C: angular gyrus
D: supplementary motor area
E: inferior parietal lobe
F: insula
Group II
G: medial temporal cortex
H: inferior temporal cortex
I: dorsolateral prefrontal cortex
J: lingual/fusiform gyrus
Group III
K: parahippocampal gyrus
Group IV
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SCA
• Seed ROI was defined in
PCC (-5,-49,40)
• For each voxels, partial
correlations were
determined with
• 1 Seed ROI signal
• 6 Motion parameters
• 1 Global mean signal
• Seed ROI correlations were
converted to z-values using
Fisher transform
• Smoothing
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SCA
• Group level two-tailed t-test to determine Z ≠ 0.0 (Pcorr < 0.05)
• Significant positive correlations for pairs of anti-correlated areas
A: posterior cingulate cortex
Group I
B: medial prefrontal cortex
C: angular gyrus
D: medial temporal cortex
E: inferior parietal lobe
F: supplementary motor area
Group II
G: insula
H: dorsolateral prefrontal cortex
I: inferior temporal cortex
J: postcentral gyrus
Group III
Group IV
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ICA
• Principal component
analysis extract 20 most
important components
• Sphering decorrelates all
components in spatial
domain
• ICA rotation transforms
decomposition into
maximally independent
components
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ICA
• Default mode component was selected based on PCC activity
• Individual independent components IC were backprojected
• Group level two-tailed t-test to determine IC ≠ 0.0 (Pcorr < 0.05)
A: posterior cingulate cortex
Group I
B: medial prefrontal cortex
C: angular gyrus
D: inferior parietal lobe
E: insula
Group II
F: supplementary motor area
G: medial temporal cortex
H: inferior temporal cortex
I: dorsolateral prefrontal cortex
Group III
Group IV
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Conjunction analysis
• Conjuncted (‘AND’) logical map was constructed from thresholded
results
A: posterior cingulate cortex
Group I
B: medial prefrontal cortex
C: angular gyrus
D: inferior temporal cortex
E: dorsolateral prefrontal cortex
F: insula
Group II
Group III
Group IV
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Discussion & Conclusion
• Two anti-correlated networks with dynamic ongoing activity
were found
• Task-negative default mode network (PCC+MPFC+IPC)
• Task-positive anti-correlated network (SMA+INS+DLPFC)
• Multiple methods reveal strong synchronization
• intra-regionally (ReHo)
• inter-regionally (SCA+ICA)
possibly for the purpose of efficient parallel processing
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Discussion & Conclusion
• Consistent findings across
• Groups
• Methods
• Some differences were observed
• ReHo more sensitive to task-negative than task-positive network
• ReHo revealed areas outside both networks with unclear resting state
function
• SCA vs. ICA: area-related vs. network-related
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Discussion & Conclusion
• Limitations
• Group differences
• Thresholding
• Physiological noise signals
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Perspective
• Default network
• Marcus Raichle coined "default-mode" in 2001 to describe resting state
brain function; the concept rapidly became a central theme in
neuroscience. The default network is a network of brain regions that are
active when the individual is not focused on the outside world and the
brain is at wakeful rest. Also called the default mode network (DMN) or
task-negative network (TNN), it is characterized by coherent neuronal
oscillations at a rate lower than 0.1 Hz (one every ten seconds). During
goal-oriented activity, the DMN is deactivated and another network, the
task-positive network (TPN) is activated. It is thought that the default
network corresponds to task-independent introspection, or selfreferential thought, while the TPN corresponds to action, and that
perhaps the TNN and TPN should be considered elements of a single
default network with anticorrelated components.
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From: Wikipedia
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Perspective
• Anatomy
• The default network is an interconnected and anatomically defined brain
system that preferentially activates when individuals focus on internal
tasks such as daydreaming, envisioning the future, retrieving memories,
and gauging others' perspectives. It is negatively correlated with brain
systems that focus on external visual signals. Its subsystems include part
of the medial temporal lobe for memory, part of the medial prefrontal
cortex for mental simulations, and the posterior cingulate cortex for
integration, along with the adjacent precuneus and the medial, lateral
and inferior parietal cortex. In the infant brain, there is limited evidence
of the default network, but default network connectivity is more
consistent in children aged 9-12 years, suggesting that the default
network undergoes developmental change.
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From: Wikipedia
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Perspective
• Function
• In humans, the default network has been hypothesized to generate
spontaneous thoughts during mind-wandering and believed to be an
essential component of creativity. It has been hypothesized to be
relevant to mental disorders including Alzheimer's disease, autism, and
schizophrenia. In particular, reduced default network activity has been
associated with autism, overactivity with schizophrenia, and impaired
control of entering and leaving the default network state is correlated
with old age. The hypothesis that the default network is related to
internally directed thought is not universally accepted. In 2007 the
concept of the default mode was criticized as not being useful for
understanding brain function, on the grounds that a simpler hypothesis
is that a resting brain actually does more processing than a brain doing
certain "demanding" tasks, and that there is no special significance to
the intrinsic activity of the resting brain.
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From: Wikipedia
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Perspective
• Some overview papers
• A default mode of brain function.
Raichle et al. (2001). Proc Natl Acad Sci USA 98 (2): 676-82.
• A default mode of brain function: a brief history of an evolving idea.
Raichle et al. (2007). Neuroimage 37 (4): 1083-90.
• Does the brain have a baseline? Why we should be resisting a rest.
Morcom et al. (2007). Neuroimage 37 (4): 1073-82.
• The brain's default network: anatomy, function, and relevance to
disease.
Buckner et al. (2008). Ann NY Acad Sci 1124: 1-38.
• Spontaneous low-frequency blood oxygenation level-dependent
fluctuations and functional connectivity analysis of the 'resting' brain.
Auer (2008). Magn Reson Imaging 26 (7):1055-64.
• Intrinsic brain activity in altered states of consciousness: how conscious
is the default mode of brain function?
Boly et al. (2008). Ann NY Acad Sci 1129:119-29.
• The maturing architecture of the brain's default network.
Fair et al. (2008). Proc Natl Acad Sci USA 105 (10):4028-32
• Default-mode brain dysfunction in mental disorders: a systematic review.
Broyd et al. (2008). Neurosci Biobehav Rev (in press)
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