Hi,
experts,
I
figure out two ways to extract VOI data for PPI analysis based on the SPM8 PPI manual, but I am not sure
which one is right. Could do you help me to check them?
Method 1:
For the GLM analysis (Design setup and estimation), I am considering to define three conditions: fixation, 0-back and 2-back in the design matrix, and define two T contrasts as follows:
For the first T-contrast, Name is Working memory, and the
T contrast vector is: 0 -1 1 (Note the order of the conditions in the design
matrix is: fixation,
0-back and 2-back).
For the second T-contrast Name is Cognition, and the T contrast vector is: -2 1 1.
Then, I will find a PFC region (PFC1)
that is activated during task and shows greater activation during 2-back
condition that during 0-back condition when I check the result using Cognition
contrast with the Working memory contrast as an inclusive mask.
Next, while extracting VOI data, I will
(1) Select Cognition contrast, but do not use mask.
(2)
Go to this PFC1 point
(3)
Press eigenvariate
(4)
Name of region [PFC1]
(5)
Adjust data for [effects of interest]
(6)
VOI definition [sphere]
(7)
VOI radius(mm) [6]
In
this way, when I create the PPI variable, the Input
variables and contrast weights should be: [2 1
-1; 3 1 1]
Method
2:
For
the GLM analysis, I think that another way is to define two conditions: 0-back and 2-back in the design matrix, and define only
one T contrast as follows:
Name is Working memory, and the T contrast vector is: -1
1 (Note the order of the conditions in the design matrix is: 0-back and 2-back).
Then, I will find a PFC region
(PFC2) showing greater activation during 2-back condition that during 0-back
condition when I check the result using the Working memory contrast.
Next, while extracting VOI data, I will
(1) Select Working memory contrast.
(2)
Go to this PFC2 point
(3)
Press eigenvariate
(4)
Name of region [PFC2]
(5)
Adjust data for [effects of interest]
(6)
VOI definition [sphere]
(7)
VOI radius(mm) [6]
In
this way, when I create the PPI variable, the Input
variables and contrast weights should be: [1 1
-1; 2 1 1]
I have highlighted the differences between the two ways.
Any
help is greatly appreciated.
Many
thanks,
Yuan