Maybe a better way to think about curvature is that it indicates whether the surface is locally above (positive) or below (negative) the tangent plane

On Jun 14, 2021, at 10:29 PM, Fischl, Bruce <BFISCHL@mgh.harvard.edu> wrote:



Sulc is the integrated dot product of the movement vector with the (outwards pointing) surface normal during inflation. In gyral regions the movement vector is consistently inwards and has a negative dot product with the surface normal, which is why it is negative.

 

As for your second question, I’m not sure I understand. The mean curvature is the average of the two principle curvatures. If you think of the surface locally as a height function over the tangent plane, then the two curvatures are the eigenvalues of the Hessian of that function (if that helps).

 

Cheers

Bruce

 

From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> On Behalf Of 1248742467
Sent: Monday, June 14, 2021 9:23 PM
To: freesurfer <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative?

 

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Hello, Fs

 In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative？

by the way, how the mean curvature reflects the degree of fold? Since the mean curvature is a local measurement, does the mean curvature map reflects the fold degree?