why would one control for total brain volume in doing vertex-based
analyses when the vertex-based measures are computed in standard space?
The vertex-based measures are computed in individual space, not standard space doug
Dear Doug,
I would like to know at what stage the measures computed in individual space are normalised, if at all, in order to make comparisons of data across participants (e.g. in qdec) meaningful. Differences in the relative position of a particular structure across participants will make it difficult if not impossible to examine effects at the group level. If the vertex-wise data is in individual space, then I’m not sure that I understand how using total brain volume as a covariate would solve the above problem. I would greatly appreciate any clarifications that you might have.
Best wishes, Narly.
The normalization is the mapping of values from the individual subject to a standard space so as to align different structures. This does not happen until you run mris_preproc or recon-all -qcache. When you normalized a thickness map, the thickness values themselves are not changed in any way, just mapped to a different location. So the location is normalized to standard space, but not the value. Does that make sense? doug
On 03/19/2014 08:22 AM, Narly Golestani wrote:
why would one control for total brain volume in doing vertex-based
analyses when the vertex-based measures are computed in standard space?
The vertex-based measures are computed in individual space, not standard space doug
Dear Doug,
I would like to know at what stage the measures computed in individual space are normalised, if at all, in order to make comparisons of data across participants (e.g. in qdec) meaningful. Differences in the relative position of a particular structure across participants will make it difficult if not impossible to examine effects at the group level. If the vertex-wise data is in individual space, then I’m not sure that I understand how using total brain volume as a covariate would solve the above problem. I would greatly appreciate any clarifications that you might have.
Best wishes, Narly.
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Douglas N Greve -
Narly Golestani