Hi Freesurfers,

I am doing a surfaced based ROI analysis on each of my subjects functional data. Using information from other papers, the size of the ROI really matters when doing the analysis, and I want to take this information from these papers and apply them to my own data. However, these papers use volume based ROI analysis, by making spheres that have 6 mm radiuses around the location of peak activity. To translate what they did to a surface based approach, I thought I would try to approximate how large this sphere would be if it were projected onto the surface of the brain by creating cubes around a certain location in the volume and projecting them to the surface using mri_vol2surf. That way, I would have approximately the same amount of information in my surface ROI. This is more of a general question, but I was wondering how this command actually works and whether it takes just one face or slice of the volume I created and projects that to the surface, or if it would project all 6 faces of the cube to the surface. And how is this volume actually translated into vertices? And how does the location of the cube in the volume space of the brain determine how large it will be on the surface? Do you have any suggestions as to how I can approach this problem better?

Thanks?!