Hi Mariana-
You can use either
3dTcorr1D or
3dttest++ (or if you want to go super old school, 3dRegAna).
If you want to use 3dTcorr1D, you can
follow instructions here.
If you'd prefer to use 3dttest++, then you can
follow the instructions here.
The nuance of 3dttest++ is to then use 3dcalc to convert the t-value to a correlation via the t to R-square method.
3dcalc -a T-stat+tlrc -expr ‘(ispositive(a)-isnegative(a))*sqrt(a*a/(a*a+DF))’ -prefix corr
The two programs will provide identical results, it's ultimately about what you're most comfortable using. If you have a series of behavioral measures, you'll need to do either of these processes in a loop, but you can use column selectors to grab the correct variable to correlate with the MRI data. 3dttest++ will figure out the matching data file, whereas 3dTcorr1D, the MRI and behavioral data must be in the same order.
