I am encountering an odd effect when using the Freesurfer maps in Brainstorm.  I have Individual activity for multiple subjects where the activity generally seems to look generally well spread across teh gyrus and sulcus in task relevant areas.  However, when I map the individual subjects onto the freesurfer average anatomy, and average the activity it's primarily in the sulcus that the activity across subjects is prevalent.  Most notably, it becomes heavily present in the Sylvian fissure. 

I was looking through the mris_register function, and it seems the sulci are used as one of the primary alignment measures, and was wondering if this could be giving rise to this propensity of the group maps to appear predominantly in the sulcus.  Looking through the settings I am not 100% clear on what all the settings do.  So I was wondering if anyone had encountered this issue before.  And what settings for the mris_register I should look at adjusting to try and correct the issue.

Thank you for your time and assistance.