Applying Functional Holography to fMRI Exploring functional asymmetry in the motor cortex as a means...

Applying Functional Holography to fMRI

Exploring functional asymmetry in the motor cortex as a means of determining hemispheric dominance

Amir Rapson, Eshel Ben-Jacob, Talma HendlerSchool of Physics – Tel Aviv University

Tel-Aviv Human Brain Mapping May 2005

FH- Functional Holography

• A new approach for analyzing complex activity in biological networks in the space of functional correlations.

• Holography – as in holograms, where a part of a hologram will still reveal an entire picture, we hope to gain the whole functional picture by sampling only part of the data

• Itay Baruchi, Vernon L. Towle and Eshel Ben-Jacob, Functional Holography of Complex Networks Activity— From Cultures to the Human Brain, Complexity 2005

Tel-Aviv Human Brain Mapping May 2005

FH- Functional Holography

• This is done by combining two parameters to find structural resemblance (affinity):

– Time propagation – by computing correlations between time sequences -

– Functional properties – by computing distances between correlations (correlation of correlations) -

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Tel-Aviv Human Brain Mapping May 2005

FH- Functional Holography

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Affinity

Combining the two is done by calculating the Affinity matrix:

ij

ijij D

CA

Tel-Aviv Human Brain Mapping May 2005

FH- Functional Holography

PCA

By reducing the number of dimensions, we get the FH manifold:

Tel-Aviv Human Brain Mapping May 2005

Applying FH to fMRI

• Motor Cortex: Unilateral hand movements– 5 hand movements for each hand– 15 seconds for each movement– Instructions to start and to end movements– Rest period of 10 seconds between movements– Every block of rest, instruction, movement, rest is

analyzed as a single event

Tel-Aviv Human Brain Mapping May 2005

Applying FH to fMRI

• Selection of ROIs, and calculating correlations between channels

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L

Tel-Aviv Human Brain Mapping May 2005

Applying FH to fMRI

• Clustering and Focusing on larger groups

Tel-Aviv Human Brain Mapping May 2005

Applying FH to fMRI

• Projecting the clusters on the brain

R

L

Tel-Aviv Human Brain Mapping May 2005

Applying FH to fMRI

• And computing the FH manifold

R

L

L Hemis

R Hemis

L Handed I, R hand movement

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

Aim:

Exploring functional asymmetry in the motor cortex as a means of

determining hemispheric dominance

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Structural functional differences between hemispheres

R

L

R Hemis

L Hemis

L Handed 1, R hand movement

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Structural functional differences between hemispheres

R Hemis

L Hemis

Tel-Aviv Human Brain Mapping May 2005

1218.70

Determining Dominance

R Hemis

L Hemis

• Calculating RG: ji

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icmig rr

Nrr

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Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Calculating RG: ji

ji

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icmig rr

Nrr

NR

,

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261.47323.29

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L

R Hemis

L Hemis

L Handed 1, R hand movement

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Calculating RG: ji

ji

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icmig rr

Nrr

NR

,

2

21

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261.47323.29

R Hemis

L Hemis

Dominance

FunctionalStructure

?

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Calculating RG: ji

ji

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Nrr

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)( DOMG

NONG

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RL Hemis

R Hemis

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Right handed subject: Right hand movement

215.17169.93

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L

R Hemis L HemisR Handed 2, R hand movement

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Right handed subject: Left hand movement

151.06291.4

R

LR Hemis

L Hemis

R Handed 2, L hand movement

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Left handed subject: Right hand movement

261.47323.29

R

L

R Hemis

L HemisL Handed 1, R hand movement

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Left handed subject: Left hand movement

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Matrix

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L

R Hemis

L Hemis

L Handed 2, L hand movement

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Average ratio nondominant/dominant of 4 subjects:

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R

R

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

• Average ratio nondominant/dominant of 4 subjects:

– Left handed 1: 0.62±0.34– Left handed 2: 0.72±0.13

– Right handed 1: 0.63±0.11– Right handed 2: 0.58±0.20

Tel-Aviv Human Brain Mapping May 2005

Determining Dominance

Discussion

• Degree of hemispheric dominance?• Acquired dominancy?• Functional rigidness and plasticity?

Tel-Aviv Human Brain Mapping May 2005

Applying FH to fMRI – Other properties

• Functional Connectivity MapsConnectivity between M1s through SMA

SMA

L M1

R M1R

L

Tel-Aviv Human Brain Mapping May 2005

Applying FH to fMRI

Thanks to:

Itay Baruchi,

Michal Kafri, Yaniv Assaf