Data Simulation

Data Simulation

RAP MUSIC Reconstruction

Previous sections of the tutorial have focused on analyzing real MEG data. In this section of the tutorial we will show you how to simulate MEG data through the use of BrainStorm. There are 2 ways of creating simulated MEG data: Using a real forward model or simulated MRI. This tutorial will guide you to create simulated MEG data using a real forward model. For this purpose you are going to use the head model that was created before (See the tutorial for Head Model).

• Select somDemo_av_headmodeVolgrid_CD from among the available head models on the BST Main window. Hint: If you don't have a head model available see the tutorial about generating a Head Model.
• Select Simulate->Subject-based data on the BST Main window menu to activate the Source Simulator.

• With Source Simulator you can create a surface and/or a volume source. Here we are going to simulate 2 sources; 1 surface and 1 volume source.

• First we are going to simulate a surface source with a gaussian input with the properties specified in next 4 steps.
• In Source Properties section write 10 in Amplitude box, this will allow us to have a time series with a maximum amplitude of 10.
• Write 200 in Duration box to simulate a 200ms input.
• Write 40 in Center box to simulate a peak at 40 ms.
• Write 10 in Width box to make the width of the input 10 ms.
• Click Plot button to see the simulated input signal.
• Make sure that cortex_10000V_tess_CTF is selected as the surface source, because we are to simulate a source on the cortical surface. To locate the source, click Plot button in Source Type section. This will open a window with the cortical surface. Select a point on this surface and click + in Source Type section to grow the patch till reaching a desired patch size.

• Click Add Source button to add this surface source to the simulation.
• Now we are going to add a volume source with sinusoidal time series to our simulation.
• In Source Properties section write 25. Realize that this input has a bigger amplitude than the surface input. Write 200 in Duration box. Write 20 in Frequency box. Click Plot button to see the simulated input signal.
• Select Volume Source in Source Type section and specify the orientation for this volume source as 1, 1, 2 for x, y z respectively.
• Click Add Source button to activate the MRI Viewer and select a source on the MRI volume. Quit the MRI Viewer to add this volume source to the simulation. Hint: Before quitting the MRI Viewer you can Select the point and name it as SimulatedSource, and Save in BrainStorm Format (you can name it as simulatedSource_subjectimage.mat). By doing so you will be able to visualize the point source using MRI Viewer, besides you will have the chance to compare the reconstructed source with the original one.

• To finish the procedure click Simulate button. Write simulated_data in save simulated data window and simulationParamaters in save simulation parameters window. Note that you have to name the simulation as *_data.mat to be able to import it to BrainStorm in later steps.

Reconstruction of Simulated Data

You can test the available reconstruction methods using this simulated data.

• First make sure to select the simulated data as the current dataset.
• Go to Data Manager -> Database-> Rescan database contents to refresh the content of the database. Select the simulatedData as the current dataset in MEG/EEG Datasets in folder section.
• Select the reconstruction method you want to use in Data Viewer. For more information about reconstruction methods, see the tutorials for: RAP MUSIC Reconstruction, Minimum Norm Imaging Reconstruction and LCMV Beamformer Reconstruction.

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