[FieldTrip] beamforming: one/two sources and subject specific ROI

"Jörn M. Horschig" jm.horschig at donders.ru.nl
Thu Dec 5 17:00:40 CET 2013

Hi Vitoria,

I also got two other remarks that might help you. On the one hand, you 
could play around with the regularization of the source reconstruction 
(lambda), that might help to get more focal sources. On the other hand, 
you can also play around with your clusteralpha, if you decrease that 
you could get spatially more defined clusters.
Oh and, don't necessarily trust the surface plots - they display a 
projection onto the brain surface, thus deeper brain activity will 
appear of neocortical origin. Of course, it looks nice for a paper :) 
But to make precise regional specific claims, an ortho plot might be 
Regarding your questions, for 1) I would agree, for 2), well you cited 
my mail, so that's the two ways I'd try :)


Vitoria Piai wrote:
> Dear FT community,
> I have (nice!) source-reconstruction results for my data (attached) 
> and now I've got a list of things I'd like to do next but I've got 
> some specific questions left.
> 1) ft_sourcestatistics detects /one /cluster (p = .002). It'd be nice 
> if I could say there are two different "sources" for my effect, one 
> temporo-parietal and one frontal. But I believe that from a source 
> reconstruction perspective, I cannot claim that. Could anyone confirm 
> that for me?
> 2) Based on the stats, I'd like to define my ROI and go back to 
> individual subjects to look at the single-trial data within this 
> detected source. (Ultimately, I'd like to correlate power within that 
> source with reaction times).
> Joern had some suggestions about how to select the ROI "I had the feeling that especially this latter approach (base ROI on GA +/- 3 cm, smooth individual subject data, select most sensitive voxel)"
> http://mailman.science.ru.nl/pipermail/fieldtrip/2013-June/006733.html
> Has anyone done something similar (or different)? Did it work out well?
> The problem I think I'll face is that my source isn't very focal (half of the left hemisphere!), so I'd be very happy to hear your thoughts on whether this analysis is even feasible...
> Thanks a lot,
> Vitoria
> -- 
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Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

P.O. Box 9101
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E-Mail: jm.horschig at donders.ru.nl
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