<qa>  What is the catecholaminergic agonist that increases extracellular dopamine in the prePsychopharmacological modulation of the catecholaminergic system can enhance some aspects of cognitive function. For example, COMT inhibitors can slightly improve working memoryexecutive function. Similarly, modafinil, a catecholaminergic agonist that increases extracellular dopamine in the prefrontal cortex was also shown to improve delay-dependent working memory. Differences in the response between individuals might be related to a number of factors, including variations in the genes. The recent finding that a polymorphism in the catechol-o-methyl-transferase COMT gene, which produces a 4 fold change in enzyme activity, accounts for 4 of the variance in performance of working memory tasks in humans suggest that COMT genotype may predict response to COMT inhibitors or to other agonists that increase catecholaminergic function in the frontal cortex. 