Hi Alan & Knut,

Isn't GI a function of surface area, i.e. GI = SurfaceAreaPial/SurfaceAreaHull, e.g.:

http://www.frontiersin.org/files/Articles/668/fninf-03-025/image_m/fninf-03-...

The hull area (denominator) normalizes for scale, so I would not expect the GI and surface area to be in lock-step, unless I had normalized the surfaces to some stereotaxic space first, which is not typically done. (Even then, that's not the same as making all denominators equal across subjects/hemispheres.)

Donna

On Oct 6, 2014, at 6:30 AM, Alan Francis alandarkenergy@gmail.com wrote:

Hi Knut:

Gryification and Surface Area are two completely different things. Surface Area, as measured by FreeSurfer, gives you the area of the surface (roughly length x breadth) of a given region of interest: e.g., Pars triangularis. It is measured in millimeter squared.

Gyrfication index, by contrast, measures the depth of the each gyri and is done after you have completed the FreeSurfer Recons. You can find more details on gyrification at the following website:

https://surfer.nmr.mgh.harvard.edu/fswiki/LGI

This explains the whole concept of gyrification.

best,

Alan

On Sun, Oct 5, 2014 at 11:51 AM, Knut J Bjuland knutjorgen@outlook.com wrote: Dear FreeSurfer experts I have run analyses on gyrification index. I was wondering if anybody could tell me what exactly is the relationship between gyrification index and cortical area. My gyrification results and area results are to a large extent similar. Am I measuring approximately the same thing?

Thank you Knut Jørgen Bjuland PhD candidate The Norwegian University of Science and Technology (NTNU) Trondheim, Norway

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