I realized that on the lastest versions of brainstorm, the mid brain (average between the pial surface and the gray matter-white matter interface) was not computed automatically when importing a freesurfer folder into brainstorm.
I know this could be done manually but is there a rationale on why this option is not done automatically?
I recently added a lot more stuff in the FreeSurfer import functions, now it reads volume labels as well.
Since the volume atlases and the mid surfaces are not useful to most users, but take a lot of space on the hard drive, I moved them to a different import format: "FreeSurfer + Volume atlases".
Try selecting this other file format, you should get the mid surfaces again.
Sorry, this is not documented correctly yet...