The Val/Val genotype was associated with faster reaction time in the math test but did not influence the performance on the CPT and Stroop tasks. In contrast to our findings, a functional MRI study revealed that abstinent smokers with the Val/Val genotype performed worse on the n-back test, a test of working memory (16). The reason for these conflicting findings regarding the influence of Val/Val genotype on cognitive performance is not clear. In previous studies, the Val/Val genotype was associated with better or worse performance across many cognitive tasks. It has been argued that while individuals with the Val/Val genotype perform worse on tasks that require cognitive flexibility, they may perform better on tasks that require cognitive stability (54). The N-back is a relatively difficult task that requires sustained attention and working memory function, while the mathematical processing task is an easier task that assesses single-digit calculations (54). We did not observe a genotype effect on the Stroop or CPT tasks.
