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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Dynamic Causal Modeling(DCM,),A Practical Perspective,Ollie Hulme,Barrie Roulston,Zeki lab,Dynamic Causal Modeling(DCM),Disclaimer,The following speakers have never used DCM.Any impression of expertise or experience is entirely accidental,.,Disclaimer The following speak,Structure,1.Quick recap on what DCM can do for you.,2.What to think about when designing a DCM experiment,3.How to do DCM.What buttons to press etc.,Structure1.Quick recap on wha,A Re-cap for Dummies,You can ask different types of questions about brain processing.,Questions of,Where,Questions of,How,A Re-cap for Dummies,Functional Specialization is a question of,Where,?,Where,in the brain is a certain cognitive/perceptual attribute processed?,What are the Regionally specific effects,your normal SPM analysis(GLM),Functional Specialization is a,Functional Integration is a question of,HOW,Experimentally designed input,How,does the system work?,What are the inter-regional effects?,How,do the components of the system interact with each other?,Functional Integration is a qu,MODEL-FREE,MODEL-DEPENDENT,Hypothesis driven,DCM!,Functional connectivity,=the temporal correlation between spatially remote areas,Effective connectivity,=the influence one area exerts over another,2 Categories of Functional integration analysis,PPI,MODEL-FREEMODEL-DEPENDENTDCM!F,DCM overview,DCM allows you model brain activity at the,neuronal level,(which is not directly accessible in,fMRI)taking into account the anatomical architecture of the system and the interactions within that architecture under different conditions of stimulus input and context.,The modelled neuronal dynamics(z)are transformed,into area-specific BOLD signals(y),by a h,emodynamic,forward,model(,),.,The aim of DCM is to estimate,parameters at the neuronal level,so that the modelled BOLD signals are most similar to the experimentally measured BOLD signals,.,DCM overviewThe aim of DCM is,Planning a DCM-compatible study,Experimental design:,preferably multi-factorial(e.g.at least 2 x 2),Static,Moving,No attent,Attent.,1.Sensory input factor,At least one factor that varies the,sensory,input changing the stimulus a perturbation,to the system,2.Contextual factor,At least one factor that varies the,context,in which the perturbation occurs.Often attentional factor,or change in cognitive set etc.,Planning a DCM-compatible stud,Planning a DCM-compatible study,TR should be as short as possible parameter b,One-sample t-test:parameter a 0,rmANOVA (in case of multiple sessions per subject),3,.,Ensure that the model you generate is able to test your,hypotheses,The model should incorporate every component of the hypothesis,Which parameters do you think,Parietal areas,V5,Direct influence,V1,Pulvinar,Indirect influence,DCM cannot distinguish between direct and indirect!,Hypotheses of this nature cannot be tested,4.Evaluate whether DCM can answer your question,Can DCM distinguish between your hypotheses?,In case of,Parietal areasV5Direct influen,1.Specify your main hypothesis and its competing hypotheses as precisely as possible using convergent evidence from the empirical and theoretical literature,2.Think specifically about how your experiment will test the hypothesis and whether the hypothesis is suitable for DCM to test.,3.Klaas emphasises that you should Test your model before conducting the experiment using synthetic data.Simulation is the key!,4.DCM is tricky,ask the experts during the design stage.They are very helpful.,1.Specify your main hypothesis,A DCM in 5 easy steps,Specify the design matrix,Define the VOIs,Enter your chosen model,Look at the results,Compare models,A DCM in 5 easy stepsSpecify,Specify design matrix,Normal SPM regressors,-no motion,no attention,-motion,no attention,-no motion,attention,-motion,attention,DCM analysis regressors,-no motion(photic),-motion,-attention,Specify design matrixNormal,Defining VOIs,Single subject:,choose co-ordinates from appropriate contrast.,e.g.V5 from motion vs.no motion,RFX:,DCM performed at 1,st,level,but define group maximum for area of interest,then in single subject find nearest local maximum to this using the same contrast and a liberal threshold(e.g.P0.05,uncorrected).,Defining VOIs Single subjec,DCM button,specify,NB:in order!,DCM button specifyNB:in ord,Can select:,effects of each condition,intrinsic connections,contrast of connections,Can select:,Output,Latent(intrinsic)connectivity(A),OutputLatent(intrinsic)con,Modulation of connections(B),Photic,Attention,Motion,Modulation of connections(B)P,Input(C),Input(C),Comparing models,See what model best explains the data,e.g.,Original Model,Attention modulates V1 to V5,Alternative Model,Attention modulates V5,?,Comparing modelsSee what mod,DCM button,compare,The read-out in MatLab indicates which model is most likely,DCM button compareThe read-o,
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