afni.nimh.nih.gov

The issue of unpooled vs. pooled in 3dttest++ is about the assumption of whether the two groups have roughly the same variability. It's hard to tell beforehand which is more appropriate. If this is of concern to you, try out both options, and see if significance difference exists.

Alternatively you can use 3dMEMA with option -unequal_variance to explore the difference in within-group variability.

Gang