InstaCorr SeedRad option

I would like to use the “SeedRad” option in InstaCorr in order to obtain correlations between a seed region to other brain regions. Does the “SeedRad” option in InstaCorr refer to the radius of the seed region in mm? Or does it refer to the number of voxels comprising the seed radius? I just want to be sure before I use this feature.

Additionally, is this seed radius reflected in all other brain regions? For example, if I choose SeedRad = 4, are the resulting correlation coefficients between the seed voxel + its 4mm radius to every other voxel + their 4mm radius? Or is the correlation simply between the seed voxel + its 4mm radius to all other voxels individually (i.e. without taking into consideration their neighboring voxels)?

Please let me know if you need me to clarify this question.

Thank you.


The SeedRad radius is in units of mm. It refers to the radius of the seed only; using this option, each voxel’s value is not updated/changed to include neighbors. There is a separate “Blur” value you can set to apply smoothing globally (the blur radius is also specified in units of mm), which would be essentially that latter effect.