[FieldTrip] Projection from sensors space to segmented brain surface

Eelke Spaak eelke.spaak at donders.ru.nl
Wed Jun 20 18:03:36 CEST 2012

Dear Andrea,

If I understand your question correctly, you just want to *visualise*
sensor space activity on a brain surface, without doing source
reconstruction first? I would advise against this. Time-frequency
power values of your planar gradient data reflect the spectral
characteristics of the magnetic gradient at the location of your
sensors. These sensors are not located at the surface of the brain,
but quite some centimeters away from it. Therefore, visualising the
data as if it were actually recorded on the brain surface, without
doing a proper transformation, is potentially misleading. It is true
that people tend to display all sorts of data in a 'topoplot' fashion,
but in that case it is clear to the audience that you are looking at a
representation in sensor-space. Have a look at ft_topoplotTFR for this
approach, if you're not already familiar with it.

If you want to display your time-frequency activity on a cortical
surface (which is of course a perfectly valid thing to want to do),
you first should map the sensor activity to source space. This mapping
is non-trivial and can be done by e.g. beamforming. See
http://fieldtrip.fcdonders.nl/tutorial/beamformer for a tutorial on
this. That tutorial ends with a surface plot.

Hope this helps!


On 20 June 2012 17:26, andrea brovelli <andrea.brovelli at univ-amu.fr> wrote:
> Dear Fieldtrip users and developpers,
> I would like to project and visualise time-frequency power values computed
> on planar gradient data at the sensors level onto the brain surface
> segmentated from the anatomial MRI of the subject.
> Can anyone suggest me how to do it in Fieldtrip ? Can anyone share the
> scripts ?
> Does anyone see any inconvenient to this visualisation ?
> Thanks a lot for you help.
> Andrea
> --
>  NEW EMAIL: andrea.brovelli at univ-amu.fr
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