[FieldTrip] mne vs lcmv methods
Belluscio, Beth (NIH/NINDS) [E]
BelluscB at ninds.nih.gov
Mon Sep 26 21:17:04 CEST 2011
Hi fellow Fieldtripers-
I am learning about the pros & cons of different methods for source localization. For some of my data sets, I want to localize evoked activity (ERFs). In one of them, I anticipated a single unilateral primary site of activation and MNE worked very nicely for this. In the second, I am using auditory stimuli and therefore anticipated bilaterally synchronous activity. As was to be expected, (I think) MNE gave a single site of activity near the midline. I tried a parallel approach, but specifying lcmv as the method for ft_sourceanalysis as follows:
cfg = [];
cfg.method = 'lcmv';
cfg.grid = leadfield_02_stim1;
cfg.vol = vol;
cfg.lambda = 1e8;
cfg.checksize = inf; %I've been inserting this and the next line because I've gotten error messages about the size. This didn't happen before, but these lines avoid the problem
cfg.checkconfig ='loose';
source3CB24_02_stim1 = ft_sourceanalysis(cfg, tlkCB24_02_stim1)
The output has a time dimension 1x601, and a pos dimension of 8196x3 dimension, but the avg.pow is only 1x8196. I interpret this to mean that the analysis averaged the power over some time interval instead of computing the power in each leadfield position for each time point. When I use the mne method, the output is clearly power for each time point, and produces a beautiful movie, as indicated in the tutorial.
My questions about the lcmv technique are:
1. Is there a fundamental difference between the lcmv approach and the mne approach whereby it cannot compute the power at each time point, but only gives a single average value for a time period?
2. If so, how do I specify the time interval of interest (ie that containing the main peak of the ERF) in ft_sourceanalysis?
3. I thought one advantage of either MNE or LCMV was that I could indicate my a priori hypothesis of the anticipated localization of the source activity. Do I do this with cfg.grid? Is there a way to indicate the number of anticipated dipoles?
Thanks in advance for your help-
Beth.
Beth Belluscio MD-PhD
Clinical Fellow
Human Motor Control Section
NINDS, NIH
301-402-3495
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20110926/2a80b1a9/attachment.html>
More information about the fieldtrip
mailing list