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We have used make_average_subject to resample the white and pial surfaces of an individual subject to ico 7 to produce surface coordinates in the standard tessellation, allowing for group analyses of cortical shape.

 

It may be worth noting that we temporarily replace the talairach.xfm in the subject’s mri/transforms directory with an identify matrix so that the resampled surfaces have the same position and shape as the native surfaces but with the standard ico 7 tesselation.

 

This resampling procedure works great with FreeSurfer version 5.3, but as of version 6.0 or 7.1.1, when a single subject is supplied to make_average_subject, it runs for a while but then eventually produces an error like this:

 

nframes = 1

Computing std/var across frames

ERROR: cannot compute std from one frame

ERROR: make_average_surface

 

While we can continue doing this resampling step using FS 5.3 (e.g., after running the initial recon with 7.1.1), we would like to stop relying on this very old version. Is there an alternative approach to re-tesellation of an individual subject’s surfaces into ico? Or could a future release of FreeSurfer include a modification to make_average_surface to allow it to once again handle a single subject as input?

 

 

 

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