[FieldTrip] Source Timecourse

[Rojas, Don]

Tony,

I don't use the LCMV beamformer, so I can't tell you what the structure of the output is, but what you need to perform a source space projection is the orientation and location information for the sources. In the DICS beamformer output, which I'm familiar with, this information would be in the source structure as follows (assuming your source output structure is called "source"):

source.pos % the position info as an n x 3 matrix, where n is the number of sources, in the same units as your volume conductor model
source.avg.ori % the orientation as an 1 x n cell array, where n is the number of locations and each cell is a 3 x 1 array of x y z orientation and n refers to the % same source in each array

So, in that case, you might find the necessary information for the peak source, in my case, as follows:

[~,ind]=max(source.avg.pow(:)); % index of the source with the maximum power in the dics output, let's say ind = 5000
ori=source.avg.ori(5000);       % orientation info
loc=source.pos(5000,:);          % location information

Then, if you get this info, you can search the archives for my posts, one of which has a detailed explanation for getting the source waveform when you have a known source location, source orientation and a volume conductor. If you want to get all the waveforms, you can of course iterate the process over the entire voxel volume, but since the leadfields are highly correlated in adjacent source locations, you will see that many of the waveforms will look essentially the same for sources within a few centimeters.

Best,

Don
-----------------------
Don Rojas, Ph.D.
Associate Professor of Psychiatry
U. of Colorado Denver Anschutz Medical Campus
Director, UCD Magnetoencephalography Lab
13001 E. 17th Pl F546
Aurora, CO 80045 USA
303-724-4994

On Aug 23, 2011, at 12:50 PM, Passaro, Antony D wrote:

Hi Fieldtrippers,

I was looking for a way to extract a time-course from each source estimated by the lcmv beamformer. I searched through the mailing list archives and came across a few emails which talked about the possibility but I was unable to find any examples explaining exactly how this process is done. I am interested in extracting the time-course over the average response rather than the individual trials, if possible. Any help would be greatly appreciated.

Thanks,
-Tony
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