[Freesurfer] Converting surface coordinates to MNI coordinates

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Hi,

I am conducting a meta-analysis on papers that have looked at local gyrification index (lGI) in Autism Spectrum Disorder (ASD) relative to typically developing (TD) peers.

All lGI papers have used the FreeSurfer software and have reported x,y,z coordinates for their significant clusters (in which lGI in ASD is different from TD).

Please help me with the below 2 questions:

1. My understanding is that these coordinates reported in lGI papers are "surface coordinates" (of fsaverage). Is this correct?

2. How can I convert these x,y,z surface coordinates to MNI space coordinates?

I'd really appreciate your reply,

Thanks so much,

Avi