Dipole scanning to select optimal dipoles in unconstrained source maps for extracting a single scout time series

I am currently trying to extract scout time series in the pars opercularis from an unconstrained LCMV beamformer source estimator. When I extract these time series I have the option to get the norm of the three orientations (producing only positive values) or obtain three separate time series, one for each orientation.

In the tutorials it is mentioned that dipole scanning can be used to select the optimal dipole orientation. How can I do this to obtain a single scout time series (not the norm) representing the optimal dipole orientation?

I tried applying dipole scanning and simply extracted scout time series, but I still obtain the norm version of the dipoles.

I think this option is not available, but I will let the experts address your question:
@John_Mosher, @Sylvain?

Thanks Francois for replying so quickly. I will await their responses. I wanted to ask a side question. There are some bad channels in my epoched data which I have removed. Do I (should I) reinterpolate them manually or would the source estimation algorithm do it automatically? Also, is there a favourable referencing method (e.g. average reference) that I should invoke?

Best,
Jae

Hello Jae:

No need to interpolate between bad channels (it does not add more information to source modeling) and no preferred option for referencing (it is simply a matter of visualization; Brainstorm performs source modeling with whatever EEG reference is specified).
Concerning your initial question, @jcmosher is the most qualified to answer your question. What I would recommend is that you extract the 3 LCMV time series from a given location and perform their PCA decomposition. I believe the first 3x1left vector would correspond to the best dipole orientation. (you need to do this using your own Matlab code)

Hope this helps,

Thanks for the advice Sylvain, I will certainly try that. If I want to look at scout signals on a trial by trial basis, would you recommend that I use Minimum Norm Imaging > current density map > constrained > median eigen value?

Something like that.

  1. open a source file and select the scout(s) which you want to see the time series
  2. then select the source files from single trials in BST’s file explorer
  3. right click and select Scout Time Series
    It will open a new figure window with the time series from the scouts from all single trials.

Hope this helps.