I am comparing a group of patients with controls. I extracted:
cortical volume, surface area, cortical thickness and gyrification
index for each subject's lobe.
Comparisons between this variables with Total Intracranial Volume as a
covariate indicated a difference in frontal and temporal lobes lGI.

what happens if you do not adjust for intracranial volume? if your patients have abnormal sized lobes then this may be obscured by controlling for head size.

However, differences were not significant for any of the other
variables.

I can´t understand these results from a biological perspective. I was
expecting that if a difference exist in lGI it would also manifest in
surface area or volume.

this paper: http://www.ncbi.nlm.nih.gov/pubmed/18267953

tells us that it is possible for smaller sized brains to have higher folding compared to bigger sized brains. however, it also states that it's much more probable for bigger sized brains to have a higher degree of folding, indeed a strong relationship is shown between brain volume, cortical surface and folding (Figs. 3 and 4c) over large parts of the cortex.

hth,
-joost

Can someone help me with an explanation for this?

Thank you.

ines

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