Hi all,
I wonder if someone
has insights into the following discrepancy between a random (RFX) and fixed
effect (FFX) result in fMRI. The essential problem is that there is a much
stronger RANDOM effects result in selected areas in which not
one single subject shows activation in their single-subject, fixed effect
analysis. There is huge "activation" spanning the lateral ventricles, and
an uncinate focus (all < 0.001), but NONE of the single subject FFX analyses
show anything like this at < 0.01.
I would certainly
expect much stronger FFX signals than RFX signals, but have never seen the
opposite-- and wouldn't expect any.
Some quick details
are:
n= 7 subects (yes, I
know, quite small, but not a final sample).
Blocked
design.
FFX analyses with
corrections for serial correlation.
The FFX results are
a somewhat complicated interaction consisting of conditions
1/1 1/2 1/1
1/2 2/1 2/2 2/1 2/2
where the number to
left of the ''/" is a drug condition (drug v placebo) and the number to the
right of '/' is a task (1 or 2).
The contrast images
analyzed consist of the drug x task interaction: 1 -1 -1 1 -1 1 1
-1.
Thanks for any
help,
David
K
David A. Kareken, Ph.D.,
ABPP/ABCN
Board Certified
Neuropsychologist
Associate Professor &
Director of Neuropsychology
Department of Neurology
(RI-1773)
Indiana University School
of Medicine
Indianapolis, IN
46202
Tel: 317
274-7327
Fax: 317
274-1337