Hi Gang,

1) Are nice and mean two separate big categories in your experimental design?
Yes
2) Aggression is a behavioral measure at the trial level that is applicable to both mean and nice categories?
Yes

As for modulation analysis, the basic model at the subject level is the following formulation

y = a + b * x + e

where x is the modulation variable (aggression in your case). What is your effect of interest at the population level between the following two?

1) a: BOLD response after controlling the aggression, or
2) b: aggression effect

I would be interested in #2 the aggression effect.

Thank you!