AFNI experts,

I am currently analyzing a data where participants underwent a memory task after two conditions (condition A and B). I already have analyzed the data using 3dttest+ by comparing the difference between the two conditions. I also would like to include a covariate (year of training) to the analysis. What I can think of is to extract the activation intensities using 3dmaskave and analyzing the activation of each condition with the covariate using SPSS or R. Is there any way I add the covariate and run multiple regression in AFNI which can show the interaction between condition and the covariate in the image?

Thank you in advance for your help,
Jun