[FieldTrip] fieldtrip Digest, Vol 40, Issue 33

Johanna Zumer johanna.zumer at gmail.com
Thu Mar 20 14:03:52 CET 2014

Hi May, Inna, everyone,

I'm not sure exactly what Inna meant by the ROI, specifically whether the
ROI was applied to source space or to sensors.   Applying a ROI to sources
will not work: the beamformer result at one location in the brain is the
same irrespective of where else you also compute a beamformer result.
However, perhaps Inna meant ROI over channels (e.g. left channels for the
left auditory cortex).  If so, then as she says, it will reduce the problem
a bit but it will still be there.   See cfg.supchan in ft_sourceanalysis.

Indeed the method by Dalal et al. was initially implemented in the NUTMEG
<http://www.nitrc.org/projects/nutmeg/>software (which is compatible with
FieldTrip).  However, it is also now implemented in FieldTrip by using the
cfg.supdip option in ft_sourceanalysis, which allows you to suppress a
region (e.g. right auditory cortex) so that you can estimate activity
elsewhere (e.g. left auditory cortex).


2014-03-20 11:47 GMT+00:00 Heng-Ru May Tan <Heng-RuMay.Tan at glasgow.ac.uk>:

>  Hi Inna,
> Thanks for the suggestions re using ROI beamforming separately and
> references. I'll give it a go.
> BTW, I wonder if those beamforming algorithms e.g. Dalal et al2006 (IEEE
> biomed. eng.) might have already been implemented somewhere... or might it
> be something that fieldtrip might/could consider adding to their
> sourceanalysis options? =)
> Thanks,
> May
>  ForwardedMessage.eml
> Subject:
> Re: [FieldTrip] Source localizing auditory steady state responses
> From:
> "McGowin, Inna" <mcgoiv0 at wfu.edu> <mcgoiv0 at wfu.edu>
> Date:
> 19/03/2014 17:21
> To:
> FieldTrip discussion list <fieldtrip at science.ru.nl><fieldtrip at science.ru.nl>
> Hey May,
>  Beamorming on correlated sources is my interest too. The problem is that
> most beamformers (I deal with SAM and vector beamformer) are going to
> suppress or/and misplace any correlated source. The way I deal with this
> problem is by creating a region of interest (around primary auditory
> cortex) and beaformer over each ROI separately.  The signal correlation
> problem is still there but with a lesser extant (I think). Here is a great
> article on this topic:
> Beamformer reconstruction of correlated sources using a modified source
> model
>  and
> Modified Beamformers for Coherent Source Region Suppression
>  Also if I localize evoked responses I always prefer dipole fitting over
> other methods, you could try the moving dipolar fitting method and have
> your wave former from the dipole t-course.
>  Let me know how it will go for you.
>  Cheers,
>  Inna
> Inna McGowin
> On Wed, Mar 19, 2014 at 12:17 PM, Heng-Ru May Tan <
> Heng-RuMay.Tan at glasgow.ac.uk> wrote:
> Hi All,
> I am trying to localize frequency specific ASSR but have not been
> successful in doing so with the 'mne' method in the ft_sourceanalysis.
> At the sensor-level the topo plots show clear bilateral generators.
> Is it possible to localize the bilateral sources using beamforming? And
> would I need to create a different forward model?
> Additionally, I would also like to retrieve the source signals and ideally
> comparing between 2 time periods within the same trial.
> I would appreciate if someone could advise or comment on how best to go
> about doing so.
> Thanks,
> May
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