Dear SPM group:
We are analysing Lyme Disease patients against group of normal controls.
Because the differences in Lyme patients are subject-specific, we compare
each patient individually against a group of controls. All scans are HMPAO
SPECTs.
For now, we are doing simple subtraction:
Lyme Patient Control Group
1 1 -1
2 -1 1
and proportional scaling is our global normalization method.
The first contrast (1 -1) yields widespread change in activity
throughout the whole brain. The second contrast (-1 1) shows a lot of
change throughout the subcortical structures, but always excluding the
cortex. These results hold for every individual comparison of a Lyme
subject against the control group.
We find these results mutually contradictory. If the first comparison
looks for increases in flow in a Lyme patient, and the second one looks
for decreases in flow in a Lyme patient, how can these two SPMs have
extensive overlapping regions (in this case, in subcortical areas)? Do we
interpret these subtractions correctly?
Your help will be much appreciated,
Vitaly Furman
Brain Imaging Lab
Columbia_Presbyterian Medical Center
New York, NY
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