Presentation is loading. Please wait.

Presentation is loading. Please wait.

FMRI: Biological Basis and Experiment Design Lecture 23: GLM in multiple voxels Errata Final project review Keeping track of space Multi-voxel GLM Before.

Similar presentations


Presentation on theme: "FMRI: Biological Basis and Experiment Design Lecture 23: GLM in multiple voxels Errata Final project review Keeping track of space Multi-voxel GLM Before."— Presentation transcript:

1 fMRI: Biological Basis and Experiment Design Lecture 23: GLM in multiple voxels Errata Final project review Keeping track of space Multi-voxel GLM Before After x

2 Erratum: ICE9 % Repeat the "experiment" a few times %%!!! Wrong way... shouldn't run the same design again and again - then %%the experimental conditions aren't nearly as randomized as they could %%be! nScans = 10; clear data for n = 1:nScans data(n,:) = caoSimulateData(neural,TR,BOLDamp,SNR,1); end % "Analyze" data... % %Check out code that does TTA... TTAlength = 20; [TTA TTAsem count] = caoComputeTTA(design,data,TTAlength); TTA_minus_baseline = TTA - repmat(TTA(:,1),[1 size(TTA,2)]); subplot(2,1,1) errorbar(repmat((0:(TTAlength-1))',[1 size(TTA,2)]),TTA,TTAsem); title(['nScans = ' num2str(nScans)]); axis tight subplot(2,1,2) errorbar(repmat((0:(TTAlength-1))',[1 size(TTA,2)]),TTA_minus_baseline,TTAsem); title(['nScans = ' num2str(nScans)]); axis tight legend(num2str(count))

3 Erratum: ICE9 % Repeat the "experiment" a few times % Right way - new trial order each repetition nScans = 10; fixedLength = 500; design = zeros(nScans,fixedLength); neural = zeros(nScans,fixedLength); data = zeros(nScans,fixedLength); for n = 1:nScans % For this, I'd built in a flag that would make the design vector the % same length each time (adding 0's at end) to deal with the fact that % randomized ISI's yield unpredictable scan lengths design(n,:) = caoMakeER(waitUpFront,nStimTypes,ISIrange,nStim,500); for nt = 1:length(design) if design(n,nt) % if there's a stimulus neural(n,nt) = relResp(design(n,nt)); % pick the appropriate response end data(n,:) = caoSimulateData(neural(n,:),TR,BOLDamp,SNR,1); end

4 Basic assignment, final project (all projects need these components) Abstract (250 words) Background - experiment design and neuroscience question motivating the experiment (1 page, 1 - 3 references) Methods (2 – 4 pages) –MR Methods section (resolution, TR, TE, protocol) –Prediction of neural activity –Prediction of BOLD response (noiseless model) –Simulated data (BOLD + noise - physiological and/or thermal) –ROI selection –GLM Results (1 – 3 pages) –Paragraph describing simulation output + 1 figure –Paragraph describing GLM results + 1 figure Discussion (1 - 2 pages) –3 things that might not be as expected if you ran the experiment

5 Building blocks, final project (weekly assignments, 2 nd half of semester) Abstract (250 words) Background - experiment design and neuroscience question motivating the experiment (1 page, 1 - 3 references) Methods (2 – 4 pages) –MR Methods section (resolution, TR, TE, protocol) – WA 8 –Prediction of neural activity – WA7 –Prediction of BOLD response (noiseless model) – WA7 –Simulated data (BOLD + noise - physiological and/or thermal) – WA8 –ROI selection –GLM – WA10 & WA11 Results (1 – 3 pages) –Paragraph describing simulation output + 1 figure – WA8 –Paragraph describing GLM results + 1 figure – WA10 & WA11 Discussion (1 - 2 pages) –3 things that might not be as expected if you ran the experiment

6 Presentation schedule Groups –Denkinger –Han, Honwanishkul, Roher –Haut, Johnson –Kruse, White –Kwon –Liu, Schmidt –Seo, Vizueta –Theodorou –Thompson Times –May 2 9:45 – 10:05 Kwon 10:05 – 10:25 Theodorou 10:25 – 10:45 Denkinger 10:45 – 11:15 Big group HHR –May 4 9:45 – 10:05 Thompson 10:05 – 10:25 Big group 10:25 – 10:45 Seo, Vizueta 10:45 – 11:15 Haut, Johnson

7 A 1,1 A 2,1 A 3,1 A 4,1 A 1,2 A 2,2 A 3,2 A 4,2 A 1,3 A 2,3 A 3,3 A 4,3 A 1,m A 2,m A 3,m A 4,m Linear model for BOLD in a single voxel A = x = x1x2x3x4x1x2x3x4 y = y1y2y3ymy1y2y3ym Ax = y Design matrix, [m x n] - m time-points - n stimulus types Data [m x 1] - response through time Responses [n x 1] - for each stimulus, a scalar (single number) representing how well that voxel responds to that stimulus...

8 A 1,1 A 2,1 A 3,1 A 4,1 A 1,2 A 2,2 A 3,2 A 4,2 A 1,3 A 2,3 A 3,3 A 4,3 A 1,m A 2,m A 3,m A 4,m Linear model for BOLD in multiple voxels A = x = x 1,1 x 2,1 x 3,1 x 4,1 y = y 1,1 y 2,1 y 3,1 y m,1 Ax = y Design matrix, [m x n] - m time-points - n stimulus types Data [m x p] - response through time Responses [n x p] - for each stimulus, a scalar (single number) representing how well that voxel responds to that stimulus x 1,2 x 2,2 x 3,2 x 4,2 x 1,p x 2,p x 3,p x 4,p y 1,2 y 2,2 y 3,2 y m,2 y 1,p y 2,p y 3,p y m,p...

9 Keeping track of voxels 2D (or 3D) array of data 1D vectorX & Y (& Z) coords =+

10 Fake experiment – distributed neural activity Brain (3 types of responses) 3 types of stimuli; 3 types of "neuron" (voxel?)

11 Fake experiment – simulated data Brain (3 types of responses) voxels (Baseline trends, noise dominate visualization)

12 Design Matrix - Stimulus 1 - Stimulus 2 - Stimulus 3 - Linear drift - Half-cycle cos drift - 1.5 cycle cos drift

13 Design Matrix + (sim.) data X= ? time voxels

14 (An aside on rows and columns) Why do [nTpts nVoxels] instead of [nVoxels nTpts]? –Typical experiment 6 scans, 200 tpts per scan --> nTpts = 1200 1 brain, 64 x 64 x 30 voxels --> nVoxels = 122,880 –Size of A [nTpts nVoxels]: [122,880 1200] [nVoxels nTpts]: [1200 122,880] –Size of A T A [nTpts nVoxels]: [1200 1200] [nVoxels nTpts]: [122,880 122,880] !

15 Estimate of voxel responses X= time voxels x est = x +  = (A T A) -1 A T (y +  )

16 Estimate of voxel responses Response to Stim1Response to Stim3Response to Stim2 Estimated Input

17 WA10 – Build design matrix & GLM analysis tool


Download ppt "FMRI: Biological Basis and Experiment Design Lecture 23: GLM in multiple voxels Errata Final project review Keeping track of space Multi-voxel GLM Before."

Similar presentations


Ads by Google