Effective Connectivity

Effective ConnectivityEffective Connectivity

Lee Harrison

Wellcome Department of Imaging Neuroscience, University College London, UK

SPM Short Course, May 2003

Outline

Motivation & conceptsModels of effective connectivityAn example

Outline


Q. In what areas does the ‘motion’ factor change activity ?

Univariate Analysis

Functional Specialization

Functional IntegrationTo estimate and make inferences about

(1)the influence that one neural system exerts over another

(2) how this is affected by the experimental context

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Concepts

Brain as a physical system Evoked response to input

System identificationParameterised models

In terms of connectivity

Classification of models Black box & hidden states

Concepts (continued)

Linear vs nonlinear systems Balance mathematical tractability and biological plausibility

Generalization of General Linear Model Bilinear models

Inputs Perturbing & contextual Stochastic & deterministic

• use of design matrix

Experimental design 22 factorial design







Model of Neuronal Activity

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Outline


1) Standard Analysis of fMRI Data

2) Statistical Parametric Maps

3) Anatomical model

4) Connectivity model

5) Estimation & inference of model parameters

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Practical stepsDesign matrix

SPMs

Outline

Motivation & conceptsModels of effective connectivity

Linear regression Convolution State-Space

An example

Outline



An example

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Inference in SEMs

Outline



An example

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Outline



An example

Outline



• Dynamic Causal Modelling

An example

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The DCM and its bilinear approximation

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intrinsicconnectivity

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Output function: a mixture of intra- and extra-vascular signal

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Activity-dependent signal

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Constraints on•Connections

•Hemodynamic parameters

Models of•Hemodynamics in a single region

•Neuronal interactions

Bayesian estimation

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Overview

1) Standard Analysis of fMRI Data

2) Statistical Parametric Maps

3) Anatomical model

4) Connectivity model

5) Estimation & inference of model parameters

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Practical stepsDesign matrix

SPMs

Outline



An example DCM for visual motion processing

A fMRI study of attentional modulation

Stimuli 250 radially moving dots at 4.7 degrees/s

Pre-Scanning

5 x 30s trials with 5 speed changes (reducing to 1%)

Task - detect change in radial velocity

Scanning (no speed changes)

6 normal subjects, 4 100 scan sessions;

each session comprising 10 scans of 4 different condition

F A F N F A F N S .................

F - fixation point only

A - motion stimuli with attention (detect changes)

N - motion stimuli without attention

S - no motion

Buchel et al 1999

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3) Attentional modulation of

prefrontal connections

That is sufficient to explain regionally specific attentional

effects2) Segregation

of motion information to

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1) Hierarchical architecture

Summary

Studies of functional integration look at

experimentally induced changes in connectivityNeurodynamics and hemodynamics

DCM

Inferences about large-scale neuronal networks

Documents

Effective Connectivity