For different reasons I found myself double checking the relationship between t-values in t.nii and p-values stored in sig.nii. If I use the following matlab code I thought that I should get the values of my_pval and stored_pval to be the same (except perhaps for the sign):

cd(fullfile(basedir,session,'bold',anal,contrast))
x=load('../X.mat')
t=MRIread('t.nii');
sig=MRIread('sig.nii');
test_voxel_number=4000;
my_pval=-log10(2*tcdf(-(abs(t.vol(test_voxel_number))), x.DOF))
stored_pval=sig.vol(test_voxel_number)

However I get:
stored_pval =

-0.4055

my_pval =

0.2804

Am I doing something wrong here? My FreeSurfer version is 4.5
Thank you!

--
Pablo Polosecki
Graduate Fellow
Laboratory of Neural Systems
The Rockefeller University
1230 York Avenue, Box 9
New York, NY 10065