Since there was a marginal (p< 0.06) complex three-way Genotype × Odor × Condition interaction in which perceived pleasantness of AO differed according to genotype during placebo, we also employed odorant pleasantness as a covariate. The Genotype × Odor interaction in the left mPFC and the right vmPFC remained significant, but the interaction in the left vmPFC became insignificant. Even so, it may be premature to entirely dismiss such genotype differences in perceived stimulus pleasantness as pertaining to an extraneous psychophysical stimulus feature, since “pleasantness” may encompass appetitive perceptions of the stimulus. The genotype effect in the VTA was less robust to alternative analyses, and became a trend when adding GG subjects or when removing the three subjects testing positive for any illicit drugs (p's < 0.06). While not affected by including the alcohol use disorder covariate, the genotype effect in the VTA also became insignificant when using perceived odorant pleasantness as a covariate.
