Tutorial

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In this section of the tutorial we will apply a minimum norm imaging reconstruction. See [1] for more information on minimum norm imaging approach.

• Go to the BST Main window ->Inverse Solutions -> Interactive to enable the Data Viewer.
• To limit the reconstruction in the 20-60ms time range (where the stimulus response is apparent in the time courses), choose Start: 20 and Stop: 60. The Step should read 0.80
• In the Analysis section select Min. Norm Imaging (LMMS) in the drop down menu. This will open the Minimum-Norm Imaging window.
• Realize that the Start and Stop values for the signal are read from the Data Viewer. Hint: You can change these values to reconstruct for a different region.

• Realize that the Noise normalization box is unchecked. This leads to a direct regularized minimum-norm solution without normalization. To normalize the reconstruction map using an estimate of the background noise variance at each cortical element, check Noise Normalization box and choose the Start and Stop points for baseline region. See the reference [1] for more information on normalization.
• Default value for Tikhonov regularization parameter is selected as 10, which selects a lambda value that is 10% of the maximum singular value of the forward field.
• Forward field normalization is selected by default which will used the column-normalized gain matrix in reconstruction.
• Leave the default values as they are and press the Go button to run the Minimum Norm algorithm for these parameters. Hint: See GUI Help for Minimum-Norm Imaging for information on output formats.
• Surface Manager should open and and Envelope Viz should display the cortical surface overlayed with the current density map. Use the slider on the Time section of the Data Viewer to move to another the time instance. Hint: Go to 45 ms and increase the threshold (move the Truncate slider to right in Surface Manager) to observe the activation on the left hemisphere.

• In the Surface Manager window, use the Actions drop down menu to select Dispatch Scouts. This will open the Cortical Scouts Manager window.
• Press Probe and choose a vertex in the cortical surface. Press Grow (+) until the patch is sufficiently large. To define more scouts simply repeat the process.
• Pressing Activate will show the time series of the sources in the selected patch. You can see the mean, max or all time series of the sources in the patch.

The results are stored in the C:\BSTDemoData\Study\somDemo_av.ds\BrainStorm\ folder in the files somDemo_av_results_Trial1_MNE_MEG_(time created).mat.

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