Dear free surfer experts,
I was wondering if someone could give me some general guidance on controlling for
multiple comparisons using clustering and FDR. This the situation. I completed an
analysis of functional data by first dividing the cortex into parcellations using
the icosahedron 5 file then exported the values to matlab. I now have a correlation
and significance value for all 10242 parcelations. My uncorrected results made
theoretical sense, topologically. However, I attempted to use an FDR procedure on
all these parcellations setting the FDR at .05 and no parcellations remained (all
values were above the .05 threshold). Because my parcelationas are likely
topologically correlated with the nearest neighboring clusters, it is my
understanding that it makes more sense to use a clustering method to first
identify clusters and then run a correction using FDR as cited in Chumbley, &
Friston 2009.
To complete clustering prior to FDR, I have projected the significance values
from the parcellations back onto the surface vertices and then run the
clustering approach described in the group analysis tutorial (mri_glmfit.sim).
I have projected these group results onto the associated vertices on the
fsaverage5 surface. However, when I run mri_glmfit.sim, no clusters remain. I
believe that I am running into this problem because I am trying to get clusters
of vertices when the data was actually analyzed using 10242 ROIs. Please note,
I have placed the correlation and significance values (from my analysis in
matlab) in a slope directory under GLM prior to running the analysis on the
significance values associated with each vertex.
By replacing the significance file generated from a thickness study with the
significance file that I created, does freesurfer conduct the same analysis
without reference to the type of data; does it only matter that I am using
significance values or should I be replacing another file in the directory (I
am using a different methodology to obtain my correlation and significance
values)? The fsgd file that is in the folder still represents the groups
correctly even though the neural data has been changed external to free surfer.
Any suggestions or appropriate literature on how to correct for multiple
comparisons using clusters of ROIs on surface would be appreciated?
Thank you,
Erik Jahner
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