Head Model

movie

Before solving the inverse problem in MEG (i.e. estimating the sources of magnetic signals when MEG measurements are available), we need to solve the forward problem (i.e. to estimate the magnetic signals when the source configuration is known). The forward problem is solved by generating a head model. In this tutorial we will create a single sphere head model, whose radius and center is estimated based on the scalp tessellation. The forward problem is solved on the cortical surface, to be used later for Min-Norm reconstructions, and in the entire head volume, to be used later for RAP-MUSIC reconstructions.

• Go to BST Main window ->Tools->Head Modeling -> Advanced to open Head Modeling Tool window
• Type somDemo in the HeadModel Name
• Tick MEG, and leave the default value Single Sphere in the Forward Modeling Method
• In the Head Compartments, choose Scalp : scalp_10000V_tess_CTF and Cortex : cortex_10000V_tess_CTF

• Click Adjust in the Best-fitting Sphere Parameters section. BrainStorm will automatically calculate the best fitting sphere based on the scalp configuration, and display it on a pop-up window.
• Make sure the Compute field is checked in the Volume Source Grid section. We will need the volume grid for RAP-MUSIC reconstructions.
• Click Run.

We just generated two head models, one for the cortical surface, and the other of the entire head volume. In C:\BSTDemoData\Study\somDemo_av.ds\BrainStorm folder, you should see the following files:

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