[FieldTrip] Dipole Orientation

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

Hi Giulia,

You can of course constrain the sourcemodel to the vertex normals. In other words, if you have a subject-specific cortical sheet, you can compute the vertex normals (ideally on a high resolution image), and project the per dipole leadfield onto that orientation. The steps would be:

- compute cortical sheet based sourcemodel
- coregister the source model to the sensor array
- compute the vertex normals
- compute the leadfields of the individual dipoles
- project the leadfields along the vertex normals.

As such, there is no specific function in FieldTrip that does this for you out-of-the-box, so that would require a bit of coding of your own.

For the visualisation of dipoles with their orientation, we have the ft_plot_dipole function, but I am not sure whether this is what you are looking for.

Best wishes,
Jan-Mathijs



On 11 Dec 2023, at 10:40, Giulia Ricci via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:

Hello Fieldtrip Community,

I am currently working on extracting time series belonging to brain ROIs, and I am specifically interested in defining source orientations in the cortex.

At the moment, I'm using the svd function to obtain, for each source, the orientation that explains the maximum variance of the dipole's signals. However, in addition to this method, I would like to explore the results obtained by constraining each source, orienting it perpendicularly to the cortex.

I am reaching out to ask whether FieldTrip provides a function for modeling dipole orientation perpendicularly to the cortex surface or if there are any suggestions within the community for achieving this goal.

Additionally, I am curious if there is a FieldTrip function for plotting or checking the resulting dipoles' orientation.

Thank you in advance.

Giulia
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