Hi Jenifer -

On Wednesday 28 January 2009 15:16:20 Juranek, Jenifer wrote:

So does the info in ?h.sulc contain sulcal depth information wrt the mean cortical surface? How does this differ from the positive values contained in the ?h.curv file?

The 'sulc' and 'curv' overlays do tend to look similar sometimes, but they in fact measure quite different things.

You are correct that the 'sulc' conveys information on how far removed a particular vertex point on a surface is from a hypothetical "mid-surface" that exists between the gyri and sulci. This surface is chosen so that the "mean" of all these displacements is zero. The 'sulc' gives a indication then of linear distance and displacements: how "deep" and how "high" are brain folds

In FreeSurfer, gyri have negative 'sulc' values, are colored green, and indicate how far "down" a point has to travel to reach this "mid-surface". Sulci have positive 'sulc' values, are colored red, and indicate how far "up" a point needs to travel to reach the mid-surface.

The 'curv' conveys information on the curvature (not distance) at a specific vertex point. The color conveys the sign, and is just an arbitrary choice. The sharper the curve, the higher the value (positive or negative). Areas with positive curvature, are colored red, and correspond to curvatures in sulci, i.e. curving "up". Areas with negative curvature are colored green, and correspond to curves pointing "down", i.e. gyri.

So, in a nutshell, the difference is that the 'curv' files contain information about curvatures, and the 'sulc' files contain information about displacement.

HTH

-=R