Hi all,
We've been running an experiment employing a simple block-type motor
task with patients and controls. Now we were looking for changes in
connectivity of motor regions. MELODIC identified a nice anatomical
region with relevance to the condition studied ("A") as a single
component, so we went for that. Dual_regression showed that this
component had a stronger connectivity to area B (also meaningful) in
patients than controls, which was nice. We confirmed this by running a
seed-voxel connectivity analysis using an anatomical seed ROI covering
the same anatomical structure A as the MELODIC component did, getting
very similar results (significantly higher connectivity in patients
between A and B).
We now were interested in whether connectivity was modulated by the
task. So, we ran a PPI according to Jill Kelly's recipe, convolving
the anatomical ROI timecourse with the task. The "main PPI effects"
for each group came up empty. But the contrast controls>patients gave
a significant blob, highlighting basically area B! Being only
physicians, we're somewhat dumbfounded by that :-)
We came up with this interpretation, and I'd be glad to hear some
opinions on it:
Patients show higher connectivity between areas A and B, independently
of task (MELODIC, seed voxel analysis). No areas correlate
significantly with area A along the motor task in each group (PPI
negative for each group). Nevertheless, modulation of connectivity
between A and B is different between groups when given a motor task
(positive contrast of the PPI data, perhaps due to a nonsignificant
anti-correlation in patients and non-significant correlation in
controls, the difference becoming significant). Baseline: there is
more "static" correlation between A and B in patients, and the ability
to modulate along a task differs, favoring controls. Is that ok so
far? Or did we run into some logical circle somewhere?
Is there any way/tool within FSL to further elucidate this issue, in
particular shedding light on the modulation issue? What could
differences be, particularly regarding the empty main effects of the
PPI?
Any help is greatly appreciated as always!
Best regards,
Cornelius
--
Dr. med. Cornelius J. Werner
Department of Neurology
RWTH Aachen University
Pauwelsstr. 30
52074 Aachen
Germany
Institute of Neuroscience and Medicine
MR Physics - INM4
Research Centre Juelich
52425 Juelich
Germany
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