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Experimental design of fMRI studies Methods & models for fMRI data analysis in neuroeconomics April 2010 Klaas Enno Stephan Laboratory for Social and Neural Systems Research Institute for Empirical Research in Economics University of Zurich Functional Imaging Laboratory (FIL) Wellcome Trust Centre for Neuroimaging University College London With many thanks for slides & images to: FIL Methods group, particularly Christian Ruff

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Overview of SPM RealignmentSmoothing Normalisation General linear model Statistical parametric map (SPM) Image time-series Parameter estimates Design matrix Template Kernel Gaussian field theory p <0.05 Statisticalinference

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Categorical designs Subtraction - Pure insertion, evoked / differential responses Conjunction - Testing multiple hypotheses Parametric designs Linear - Adaptation, cognitive dimensions Nonlinear- Polynomial expansions, neurometric functions Factorial designs Categorical- Interactions and pure insertion Parametric- Linear and nonlinear interactions - Psychophysiological Interactions Overview

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Aim: –Neuronal structures underlying a single process P? Procedure: – Contrast: [Task with P] – [control task without P ] = P the critical assumption of „pure insertion“ - Neuronal structures computing face recognition? Example: Cognitive subtraction

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- P implicit in control task ? „Queen!“ „Aunt Jenny?“ „Queen!“ „Aunt Jenny?“ „Related“ stimuli „Related“ stimuli - Several components differ! „Distant“ stimuli „Distant“ stimuli Name Person! Name Gender! - Interaction of task and stimuli (i.e. do task differences depend on stimuli chosen)? - Interaction of task and stimuli (i.e. do task differences depend on stimuli chosen)? Same stimuli, different task Same stimuli, different task Cognitive subtraction: Baseline problems

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Experimental design Word generationG Word repetitionR R G R G R G R G R G R G G - R = Intrinsic word generation …under assumption of pure insertion A categorical analysis

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Categorical designs Subtraction - Pure insertion, evoked / differential responses Conjunction - Testing multiple hypotheses Parametric designs Linear - Adaptation, cognitive dimensions Nonlinear- Polynomial expansions, neurometric functions Factorial designs Categorical- Interactions and pure insertion Parametric- Linear and nonlinear interactions - Psychophysiological Interactions Overview

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One way to minimise the baseline/pure insertion problem is to isolate the same process by two or more separate comparisons, and inspect the resulting simple effects for commonalities A test for such activation common to several independent contrasts is called “conjunction” Conjunctions can be conducted across a whole variety of different contexts: tasks stimuli senses (vision, audition) etc. Note: the contrasts entering a conjunction must be orthogonal ! Conjunctions

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Example: Which neural structures support object recognition, independent of task (naming vs viewing)? A1A2 B2B1 Task (1/2) Viewing Naming Stimuli (A/B) Objects Colours Visual ProcessingV Object Recognition R Phonological RetrievalP Object viewing (B1)V,R Colour viewing (A1)V Object naming (B2)P,V,R Colour naming (A2)P,V (Object - Colour viewing) [ ] & (Object - Colour naming) [ ] [ V,R - V ] & [ P,V,R - P,V ] = R & R = R Price et al Common object recognition response (R ) A1 B1 A2 B2

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Conjunctions

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Test of global null hypothesis: Significant set of consistent effectsTest of global null hypothesis: Significant set of consistent effects “Which voxels show effects of similar direction (but not necessarily individual significance) across contrasts?” Null hypothesis: No contrast is significant: k = 0 does not correspond to a logical AND ! Test of conjunction null hypothesis: Set of consistently significant effectsTest of conjunction null hypothesis: Set of consistently significant effects “Which voxels show, for each specified contrast, significant effects?” Null hypothesis: Not all contrasts are significant: k < n corresponds to a logical AND A1-A2 B1-B2 p(A1-A2) < + p(B1-B2) < + Friston et al.Neuroimage, 25: Friston et al. (2005). Neuroimage, 25: Nichols et al. (2005). Neuroimage, 25: Two types of conjunctions

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SPM offers both types of conjunctions Friston et al.Neuroimage, 25: Friston et al. 2005, Neuroimage, 25: specificity sensitivity Global null: k = 0 (or k<1) Conjunction null: k < n

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F-test vs. conjunction based on global null Friston et al.Neuroimage, 25: Friston et al. 2005, Neuroimage, 25: grey area: bivariate t-distriution under global null hypothesis

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Using the conjunction null is easy to interpret, but can be very conservative Friston et al.Neuroimage, 25: Friston et al. 2005, Neuroimage, 25:

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Categorical designs Subtraction - Pure insertion, evoked / differential responses Conjunction - Testing multiple hypotheses Parametric designs Linear - Adaptation, cognitive dimensions Nonlinear- Polynomial expansions, neurometric functions Factorial designs Categorical- Interactions and pure insertion Parametric- Linear and nonlinear interactions - Psychophysiological Interactions Overview

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Parametric designs Parametric designs approach the baseline problem by: –Varying the stimulus-parameter of interest on a continuum, in multiple (n>2) steps... –... and relating measured BOLD signal to this parameter Possible tests for such relations are manifold: Linear Nonlinear: Quadratic/cubic/etc. (polynomial expansion) Model-based (e.g. predictions from learning models)

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Parametric modulation of regressors → inverted ‘U’ response to increasing word presentation rate in the DLPFC SPM{F} Polynomial expansion: f(x) ~ f(x) ~ b 1 x + b 2 x 2 + b 3 x 3... Linear Quadratic F-contrast [0 1 0] on quadratic parameter SPM offers polynomial expansion as option for parametric modulation of regressors Büchel et al. 1996, NeuroImage 4:60-66

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Parametric modulation of regressors by time Büchel et al. 1998, NeuroImage 8:

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“User-specified” parametric modulation of regressors Polynomial expansion & orthogonalisation Büchel et al. 1998, NeuroImage 8:

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Investigating neurometric functions (= relation between a stimulus property and the neuronal response) Stimulus awareness Stimulus intensity Pain intensity Pain threshold: 410 mJ P1 P2 P3 P4 P0-P4: Variation of intensity of a laser stimulus applied to the right hand (0, 300, 400, 500, and 600 mJ) Büchel et al. 2002, J. Neurosci. 22:

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Neurometric functions Stimulus presence Pain intensity Stimulus intensity Büchel et al. 2002, J. Neurosci. 22:

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Model-based regressors general idea: generate predictions from a computational model, e.g. of learning or decision-making Commonly used models: –Rescorla-Wagner learning model –temporal difference (TD) learning model –Bayesian learners use these predictions to define regressors include these regressors in a GLM and test for significant correlations with voxel-wise BOLD responses

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Model-based fMRI analysis Gläscher & O‘Doherty 2010, WIREs Cogn. Sci.

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Model-based fMRI analysis Gläscher & O‘Doherty 2010, WIREs Cogn. Sci.

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TD model of reinforcement learning appetitive conditing with pleasant taste reward activity in ventral striatum and OFC correlated with TD prediction error at the time of the CS O‘Doherty et al. 2003, Neuron

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Learning of dynamic audio-visual associations CS Response Time (ms) ± 650 or Target StimulusConditioning Stimulus or TS p(face) trial CS 1 2 den Ouden et al. 2010, J. Neurosci.

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Bayesian learning model observed events probabilistic association volatility k v t-1 vtvt rtrt r t+1 utut u t+1 Behrens et al. 2007, Nat. Neurosci.

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posterior pdf ProbabilityVolatility posterior pdf

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PutamenPremotor cortex Stimulus-independent prediction error p < 0.05 (SVC ) p < 0.05 (cluster-level whole- brain corrected) p(F) p(H) BOLD resp. (a.u.) p(F)p(H) BOLD resp. (a.u.) den Ouden et al. 2010, J. Neurosci.

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Categorical designs Subtraction - Pure insertion, evoked / differential responses Conjunction - Testing multiple hypotheses Parametric designs Linear - Adaptation, cognitive dimensions Nonlinear- Polynomial expansions, neurometric functions Factorial designs Categorical- Interactions and pure insertion Parametric- Linear and nonlinear interactions - Psychophysiological Interactions Overview

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Main effects and interactions A1A2 B2B1 Task (1/2) Viewing Naming Stimuli (A/B) Objects Colours Colours Objects Colours Objects Colours Objects Colours Objects interaction effect (Stimuli x Task) (Stimuli x Task) ViewingNaming Main effect of task:(A1 + B1) – (A2 + B2)Main effect of task:(A1 + B1) – (A2 + B2) Main effect of stimuli: (A1 + A2) – (B1 + B2)Main effect of stimuli: (A1 + A2) – (B1 + B2) Interaction of task and stimuli: Can show a failure of pure insertionInteraction of task and stimuli: Can show a failure of pure insertion (A1 – B1) – (A2 – B2)

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Example: evidence for inequality-aversion Tricomi et al. 2010, Nature

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Psycho-physiological interactions (PPI) We can replace one main effect in the GLM by the time series of an area that shows this main effect. E.g. let's replace the main effect of stimulus type by the time series of area V1: Task factor Task A Task B Stim 1 Stim 2 Stimulus factor T A /S 1 T B /S 1 T A /S 2 T B /S 2 GLM of a 2x2 factorial design: main effect of task main effect of stim. type interaction main effect of task V1 time series main effect of stim. type psycho- physiological interaction

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PPI example: attentional modulation of V1→V5 attention no attention V1 activity V5 activity SPM{Z} time V5 activity Friston et al. 1997, NeuroImage 6: Büchel & Friston 1997, Cereb. Cortex 7: V1 V1 x Att. = V5 V5 Attention

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PPI: interpretation Two possible interpretations of the PPI term: V1 Modulation of V1 V5 by attention Modulation of the impact of attention on V5 by V1. V1V5 V1 V5 attention V1 attention

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Thank you

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