Daniel,

A few points:

(1) You don't need to extract the PPI interaction term value around the given voxel. You can use the PPI contrast images in a higher level analysis with your behavioral measure as a regressor. Once you have the PPI contrast images, the analysis is the same as your task activation analyses.

(2) If you have more than 2 conditions in your experiment (e.g. A, B, fixation or A, B, C, etc.), you should create separate PPI terms for each condition or create a series of PPI terms that span the experimental space (McLaren et al. 2012). This can be done in FSL as well as SPM. The only difference between the programs is the deconvolution step in the SPM implementation of gPPI through the gPPI toolbox.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Wed, Jun 4, 2014 at 3:49 PM, Yang, Daniel <[log in to unmask]> wrote:

Answering my own question, I think one simple way to do this is to retrieve the PPI interaction term value at the VOI around a given voxel that is functionally connected to the seed region. Then one can calculate the correlation between the behavioral measure and the retrieved PPI interaction term value.

Best,

Daniel

From: <Yang>, Daniel Yang <[log in to unmask]>
Reply-To: "[log in to unmask]" <[log in to unmask]>
Date: Wednesday, June 4, 2014 at 3:10 AM
To: "[log in to unmask]" <[log in to unmask]>
Subject: [FSL] PPI analysis: retrieve the connectivity

Dear all,

After performing a PPI analysis, I’d like to test if a behavioral measure is correlated with the connectivity between two brain regions in condition A versus condition B.

Could you suggest a direction to calculate an index for the functional connectivity between the two brain regions?

For example, if I have conditions A and B, and I also have the time course of a seed region and the time course of a region that is functionally connected in the PPI, how should I proceed? I am aware that there may be HRF issue and centering/demeaning issue involved.

Thanks!

Daniel