Hi Luca,
If you’re looking for the iCoh as calculated by Nolte et al. 2004 (and all the papers that refer to that one), I believe the calculation is slightly different to that which is implemented in Brainstorm. To get directional values between -1 and +1 as per Nolte, you can change the code a bit, note that when you update brainstorm I think it will be overwritten.
To modify, edit bst_cohn (save yourself a backup copy with a different name)
Change Line 244: from Gxy = imag(Gxy).^2 ./ (1-real(Gxy).^2);
To:
Gxy = imag(Gxy);
Run your iCoh as usual (plot output on a red to blue, or whatever).
I believe that’s what’s described in the math in Nolte 2004 and also in Bastos & Schoffelen 2016. Note that B & S point out that the directionality interpretation is only valid under ideal unidirectional conditions (see B & S p. 5), so it might be better to look at directionality with another connectivity method, but I’m using iCoh as a first look in order to compare with some published work.
Hope that helps.
Emily Coffey