[FieldTrip] Calculate epoched time-series in source space (ROI)

[Schoffelen, J.M. (Jan Mathijs)]

Dear Myrto,

I think that what you ask is ‘how do I create a (set of) virtual channel(s)?’

There is no dedicated documentation for this  yet. First of all, I think that you need to look into source reconstruction. After computing the forward model (a.k.a. as the leadfields) you need to use this in order to ’source reconstruct’ the channel level data, using some sourceanalysis method. More precisely, you need to compute an 'inverse operator’ which can be used to left multiply your sensor data with, in order to obtain single epoch time course of the ‘virtual channels’.

The virtual channels can be computed using the ft_virtualchannel function. Yet, in order to be able to use this, you need to use ft_sourceanalysis first.

Best wishes,
Jan-Mathijs


On 9 Jun 2021, at 16:38, Myrto Mantziara via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:

Dear Fieldtrip Team,

I would like to extract epoched EEG data from dipole sources in a Region of Interest (ROI). For the forward solution in the source analysis, I reconstructed the sources using the standard BEM headmodel (found in the Fieldtrip directory: fieldtrip-20160814\template\headmodel\standard_bem.mat) and computed the leadfield. Now I would like to apply the dipole leadfield weights to extract epoched time-series from dipoles of interest, e.g., all dipoles located in the primary motor cortex. In other words, I would like to examine the epoched data in source space (amplitude for each dipole for MVPA analysis, and time-frequency data averaged across the ROI). Also, we are not sure which leadfield weight to include (dipole orientations).
Last, do you have a function that does such weighting correctly to achieve orthogonalization in the contribution of other sources (e.g., nearby to the ROI sources) in order to increase specificity.
Perhaps there is an example code or other functions which I have not come across.

We would appreciate your help.


Regards,
Myrto Mantziara


--------------------
Myrto Mantziara
PhD Candidate
School of Psychology
Bangor University
United Kingdom
Email: m.mantziara at bangor.ac.uk<mailto:m.mantziara at bangor.ac.uk>
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