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type="cite">
Yes, those activations were located within the basal ganglia ... and it
does not make a lot of sense (at least if it is the only activation that
'survived'). I also ran these analyses in a larger sample (22 subjects).
The first versus second level discrepancy also occured. The
normalization seemed to be ok. Nevertheless, we also applied a
non-linear normalization, but the 'unusual' results remained. I'll check
the amount of movement again.
I attached some of the results again. I think the first file was to
large for the mailing list.
Thanks again,
Kirsten
---------------------------------------------------------
Dr. Kirsten Labudda, Dipl.-Psych.
Krankenhaus Mara
MRT-Abteilung
Tel.: 0521-772 777 61
&
Station für Psychosomatische Epileptologie
Tel.: 0521-772 789 22
---------------------------------------------------------
Chris Watson <[log in to unmask]> 7.11.2012
17:46 >>>
Is that bilateral thalamic and caudate activation? Is that something
that makes sense for your experiment?
I think what you're seeing *could* be due to only having 9 subjects;
however, if you see the standard L frontal activation in most/all of
them, then I don't know what might be causing the discrepancy. Is there
an especially high amount of motion in these subjects? Does the
normalization look right?
On 11/07/2012 11:46 AM, Kirsten Labudda wrote:
Dear Chris,
thanks for your quick response. I attached the screenshots of both
first and second level analyses versions I conducted (version 1:
only
the activation condition was modelled; version 2: activation and
rest
was modelled on the first level) in the small group. I used the
movement
parameters as regressors in the first level analysis. The second
level
results are thersholded at p<.001 as only very few voxel survived
the
thershold of p<.05 FWE corrected on the second level.
Thanks for your help!
Kirsten
---------------------------------------------------------
Dr. Kirsten Labudda, Dipl.-Psych.
Krankenhaus Mara
MRT-Abteilung
Tel.: 0521-772 777 61
&
Station für Psychosomatische Epileptologie
Tel.: 0521-772 789 22
---------------------------------------------------------
Chris Watson<[log in to unmask]> 7.11.2012
16:38>>>
Can you post screenshots of your design matrix, the results of 1st
and
2nd-level analyses, etc?
Regarding your design: you only need one regressor, for the task. A
contrast of "1" will reflect "task> rest".
You also might want to exclude the movement parameters, if your
experiment is a block design. Check what the literature says on that
matter.
On 11/07/2012 09:46 AM, Kirsten wrote:
Dear fMRI-experts,
we wonder about conflicting results of the first and second level
analysis we conducted with our fMRI data. We used a simple blocked
verbal fluency task with one activation condition (verbal fluency,
10
blocks) and a rest condition (also 10 blocks). I wonder, whether we
did
something wrong when using SPM (we used SPM8 and 5 and have the
problem
with both versions). That’s what we did: After preprocessing
(realignment, normalization, smoothing), we conducted a first level
analysis specifying the verbal fluency blocks as activation condition
in
each subject (by entering the onset scans of each block and its
duration
in terms of scans) and used the movement parameters as individual
regressors. We defined two contrasts (verbal fluency: 1 and rest:
-1).
Is it ok not to model the resting condition separately? We thought so
as
our design only includes two conditions and with that the vector 1
automatically contains the information activation> rest, right?
Nevertheless, I also conducted the first level analysis with the two
conditions modeled separately using two T-contrasts then (verbal
fluency> rest: 1 -1 and rest>verbal fluency -1 1). Both first
level
procedures lead to very similar results reflecting typical cortical
language activations.
I then used the contrast images (the activation condition>rest,
again
of both first level procedures described above) in the second level
analysis to run a one-sample t-test with the contrasts: activation>
rest: 1 and rest>activation: -1. Surprisingly, the typical cortical
language activation from the first level analysis completely
disappeared. Instead, only subcortical activation remained (that was
present in the first level analysis, too, but it was much weaker
than
the typical language activation).
We have the problem of very incongruent first and second level
results with SPM5 and 8 and within two different patient groups (one
was
small having 8 subjects only, but the other group includes 22
subjects).
Does anybody have an idea why the first and second level results
are
so divergent? Did we simply do something wrong in SPM?
Thanks in advance,
Kirsten
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