Dear Jin

SPM is not setup to transparently deal with multisession studies. This is the reason that many
times people will concatenate multisession runs into a single session (and include user defined
block effects) as it makes plotting graphs, extracting VOI data, etc. much easier.

However, it is possible with a bit of extra work to analyze multisession data. In your case, SPM
requires you to save VOI's from each session in your design. Thus you have to select the SPM.mat
file 6 times in order to save 6 VOI_#.mat files as you have done.

The PPI machinery then requires you to run the PPI algorithm 6 times. Each time you will select one
of the VOI_# files and it will save a PPI_# file. Once you have done this you can setup your PPI
design. You will need to load each of the PPI files into the matlab workspace, for example.

PPI1 = load('PPI_1.mat');
PPI2 = load('PPI_2.mat');
.... etc.

Choose a multiple regression fMRI design. You will have 18 user defined variables if you set this
up as separate sessions. The covariates for each session will be PPI.Y, PPI.P, PPI.ppi x 6 sessions = 18

So for the first few variables the columns of your design will be

PPI1.PPI.Y PPI1.PPI.P PPI1.PPI.ppi PPI2.PPI.Y PPI2.PPI.P PPI2.PPI.ppi ... etc.

The ppi inferences will be based on the ppi colums, [0 0 1 0 0 1 .... ]

good luck,
darren






==============Original message text===============
On Thu, 27 Jul 2006 8:20:41 am CDT "Fan, Jin" wrote:

Dear SPM and PPI experts,

When I perform the PPI analysis using SPM2 with 6 sessions for each subject, I select a ROI and the
VOI_1.mat … VOI_6.mat are saved out after pressing the VOI button and selecting each session one
by one. When I conduct the PPI analysis, I repeat 6 times and select the VOI_1.mat … VOI_6.mat
files one by one in order to save the 6 PPI output files. SPM2 asks to load the SPM.mat file each
time. My question is that: does the PPI analysis for each VOI need to match to its corresponding
session in the SPM.mat. As I read from the ppi matlab code, it matches the sessions automatically.
Am I correct?

I have an event related cue-target paradigm with cue (3 types) appears a couple of seconds before
the target (2 types). I am just interested in the connectivity for the target related activation.
I modeled the cue and target events with different vectors and used motion correction parameters as
covariates. My question is that: after I create the PPI.mat file with PPI.ppi, PPI.P, and PPI.Y
for the target (target type 1 – target type 2), when I model the connectivity, do I still need to
put in the vectors for cues and/or the motion related vectors?

Thank you!
Jin
===========End of original message text===========



--------------------------------
Darren R. Gitelman, M.D.
Cognitive Neurology and the Alzheimer's Disease Center
Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611
Voice: (312) 908-9023 Fax: (312) 908-8789
--------------------------------