Hi Wolff
an ROI can be sigificantly different without any individual vertex being
significant. It means the vertex measures are noisy in all likelihood, but
the noise averages out in the larger number of measurements.
cheers
Bruce
On Mon, 11 Feb 2013, Wolff
Schlotz wrote:
Dear Anderson (and all),
Many thanks for your reassuring response, but I am still puzzled about the
lack of association between mean area (rh_medialorbitofrontal_area) and area
in qdec (see area.png). I thought that technically there must be larger
areas for vertices within medialorbitofrontal?
Best wishes,
Wolff
>>> "Anderson M. Winkler" <wink...@fmrib.ox.ac.uk> 11.02.2013 14:22 >>>
Dear Wolff,
There is nothing wrong with your results. Your finding is one more
confirmation that thickness and area are indeed different traits, which are
influenced differently by different genetic and/or environmental factors,
and should not be confused one with another. They represent different
aspects of brain morphology and its development, and can (and should) be
analyzed and interpreted each on its own right.
It is also evidence that more power can be gained by using these two
measurements separately, rather than mixed up as in methods that only
measure gray matter volume.
Assuming you did everything else correctly, your results look perfectly fine
to me.
All the best!
Anderson
2013/2/11 Wolff Schlotz <wolff.schl...@psychologie.uni-regensburg.de>
Dear Freesurfer experts,
I tested associations between a continuous predictor and thickness and
area in qdec (and command line mri_glmfit, which gives the same
results) and found a cluster being negatively associated with
thickness orbitofrontal, but nothing for area orbitofrontal. After
exporting mean thickness and area values from aparc.stats into Stata,
consistent with my expectation I found a significant negative
correlation with my predictor for thickness. However, I also found a
significant positive association between birth weight and area.
To check what might be wrong I tested correlations between mean
medialorbitofrontal thickness from rh.aparc.thickness and thickness in
qdec and did the same for area. As expected, large average thickness
values were positively associated with thickness in
medialoribotfrontal and adjacent areas (see attached qdec screenshot
thickness.png), but there were no associations using area (see
attached qdec screenshot area.png). My expectatioin was that there
should be positive area associations similar to those for thickness.
Hence my question: Is this expectation correct? If yes, why this
discrepancy between thickness and area?
Thank you.
Wolff
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