In the estimation of current source density, MNE-Python uses a stiffness and a regularization parameter. Whereas the stiffness parameter is described in the (Perrin et al., 1989) paper of CSD, I have not seen any reference to regularization. Is the addition of regularization is something specific to MNE-Python or is it follow some previously published work?
It seems to me as the regularization parameter can be used to control the spatial scale of the information in the CSD but I am tempted to set the regularization to 0 to use the “vanilla” implementation of CSD. However, since MNE-Python default is not 0, I imagine the default value (10^-5) has been validated and found to be optimal in some regard. If such validation exists (aside from Transform EEG data using current source density (CSD) — MNE 0.23.dev0 documentation), it would be great to know where it is published.