Milena,

> was wondering whether it would have been better to just center both variables outside of 3dlme, then just
> multiply the two to get BC, and then enter centered percHDD, cravP and the two multiplied (i.e., BC) in the
> data table while listing zeroes under qVarCenters for all three variables (CravP, percHDD and BC)?

Yes, it makes more sense to manually center both variables for craving and binge drinking, and then add the product of their centered values. Also, set the center values as

-qVars 'Age,DaysDrk,percHDD,CravP,BC' \
-qVarCenters '35.9,17.26,0,0,0' \

>> Let's say I found a significant activation in putamen for the following contrast:
>> -gltLabel 1 'Male_stress_HDD_CravP' -gltCode 1 'Gender : 1*Male Task : 1*stress BC :' \
>> What's the best way to follow up that finding? I.e., how do I interpret this increased activation in the putamen?

For this interaction, the following two lines may help you sort out their interrelationship.

-gltCode 1 'Gender : 1*Male Task : 1*stress percHDD :'
-gltCode 1 'Gender : 1*Male Task : 1*stress CravP :'

Keep in mind that linearity is assumed in the current model. If nonlinearity exists, that may complicate the situation.

Gang