Interhemispheric connectivity: what is the functional role of the corpus callosum

1
Inter-hemispheric connectivity what is the
functional role of the corpus callosum?

• Klaas Enno Stephan
• Wellcome Dept. of Imaging Neuroscience
• London

With many thanks to Karl Friston, Will Penny,
Lee Harrison, John Marshall Gereon Fink
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Theories on inter-hemispheric integration
Information transfer(for left-lateralised task)
Inhibition/Competition
Processing mode setting(recruitment of
additional hemisphere)
T
T
RVF
T
-

??

-

T
LVF
T
T
LVF
RVF
Predictions modulation by task conditional on
visual field asymmetric connection strengths
Predictions modulation by task only negative
symmetricconnection strengths
Predictions modulation by task only positive
symmetricconnection strengths
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Dynamic Causal Modelling (DCM)
Neural state equation
The bilinear model
intrinsic connectivity
input u1(t)
modulation of connectivity
t
direct inputs
input u2(t)
integration
t
neuronal states
activity z2(t)
activity z3(t)
activity z1(t)
hemodynamic model
BOLD
y
y
y
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SPM results from a study on lateralisation
Does the word contain the letter A or not?
letter decisions gt spatial decisions
group analysis (random effects),n16, plt0.05
corrected analysis with SPM2
time
Is the red letter left or right from the midline
of the word?
spatial decisions gt letter decisions
Stephan et al., Science 2003
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A
C
VF
RVF
LVF
LD
LD
LD
Bind
LD,RVF
LD,LVF
Bcond
LDRVF
LDLVF
RVF stim.
LVF stim.
B
VF
LD
Bind
Bcond
D
LD
LVF
LD
LVF
LDLVF
RVF
RVF
LDRVF
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Left MOG -38,-90,-4
Left FG -44,-52,-18
Right MOG -38,-94,0
Right FG 38,-52,-20
LDLVF
0.20 ? 0.04
0.00 ? 0.01
0.07 ? 0.02
LDgtSD, plt0.05 cluster-level corrected (plt0.001
voxel-level cut-off)
plt0.05 cluster-level corrected (plt0.01
voxel-level cut-off)
0.27 ? 0.06
0.11 ? 0.03
LD
LD
0.01 ? 0.03
0.00 ? 0.04
0.01 ? 0.01
Left LG -12,-70,-6
Left LG -14,-68,-2
0.06 ? 0.02
0.01 ? 0.01
RVF stim.
LVF stim.
LDRVF
LDgtSD masked incl. with RVFgtLVF plt0.05
cluster-level corrected (plt0.001 voxel-level
cut-off)
LDgtSD masked incl. with LVFgtRVF plt0.05
cluster-level corrected (plt0.001 voxel-level
cut-off)
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Dorsal stream spatial decisions
SD
0.09 ? 0.03
0.00 ? 0.01
0.06 ? 0.04
0.10 ? 0.02
SD
SD
0.05 ? 0.02
-0.04 ? 0.02
Left Cuneus -12,-96,4
Right Cuneus 18,-96,12
0.06 ? 0.02
0.02 ? 0.01
RVF stim.
LVF stim.
SD
RVFgtLVF masked excl. with LDgtSD plt0.05
cluster-level corrected (plt0.001 voxel-level
cut-off)
LVFgtRVF masked excl. with LDgtSD plt0.05
cluster-level corrected (plt0.001 voxel-level
cut-off)