Hi @urielias !
This is not yet possible in Nilearn, but it is possible in the underlying brainsprite library that it calls: https://brainsprite.github.io/ Unfortunately, I don’t know that there is an easy snippet of code that you can draw from as an example, here, though @pbellec will be the authority on this !
There are of course other viewers that allow for “yoking” two images – this thread might be helpful, here : Looking for image viewer that is capabale of opening multiple images at once