help
help > RE: How to look at global connectivity
Jul 23, 2014 04:07 AM | Alfonso Nieto-Castanon - Boston University
RE: How to look at global connectivity
Hi Eileen,
There are several ways to measure "global connectivity" with each voxel. If by "correlation strength of each voxel with all of the other voxels" you mean the average of the connectivity between a voxel and all of the other voxels, then use the Integrated Local Correlation (ILC) measure and set the kernel size to inf (in order to consider the correlations with all other voxels, not just the correlations with neighboring voxels). If, on the other hand, you mean the norm (root mean square) of the connectivity between a voxel and all of the other voxels, then use the Intrinsic Connectivity Contrast (ICC) measure. Both measures are relatively similar, but they treat anti-correlations differently (using ILC, regions with strong anti-correlations with a given voxel tend to lower your global measure at that voxel, while using ICC it is the absolute value of the correlations what determines the global strength, not their signs). In any way, looking at the paper you mention I believe they used the former measure (average) there, so if you want to replicate those analyses I would use the ILC measure instead.
Hope this helps
Alfonso
Originally posted by Eileen Persichetti:
There are several ways to measure "global connectivity" with each voxel. If by "correlation strength of each voxel with all of the other voxels" you mean the average of the connectivity between a voxel and all of the other voxels, then use the Integrated Local Correlation (ILC) measure and set the kernel size to inf (in order to consider the correlations with all other voxels, not just the correlations with neighboring voxels). If, on the other hand, you mean the norm (root mean square) of the connectivity between a voxel and all of the other voxels, then use the Intrinsic Connectivity Contrast (ICC) measure. Both measures are relatively similar, but they treat anti-correlations differently (using ILC, regions with strong anti-correlations with a given voxel tend to lower your global measure at that voxel, while using ICC it is the absolute value of the correlations what determines the global strength, not their signs). In any way, looking at the paper you mention I believe they used the former measure (average) there, so if you want to replicate those analyses I would use the ILC measure instead.
Hope this helps
Alfonso
Originally posted by Eileen Persichetti:
I am wondering how/if its possible to look at
global based connectivity through CONN. Global based connectivity
assesses the correlational strength of each voxel with all the
other voxels in the brain. I see that in the manual there is
Intrinsic Connectivity Contrast, it seems that this is basically
the same as global based connectivity but I wanted to be sure. If
it is, how can I extract the measures for each subject to see
whether we can replicate at all the previous findings in this paper
(Relationship of resting brain hyperconnectivity and
schizophrenia-like symptoms produced by the NMDA receptor
antagonist ketamine in humans.
Driesen NR)?
Thanks,
Eileen
Driesen NR)?
Thanks,
Eileen
Threaded View
| Title | Author | Date |
|---|---|---|
| Eileen Persichetti | Jul 22, 2014 | |
| Alfonso Nieto-Castanon | Jul 23, 2014 | |