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PHARMACOLOGICAL manipulation of brain dopamine concentration affects visuospatial working memory in humans and in animals, the latter effects localized to the prefrontal cortex. However, the effects of dopamine agonists on humans are poorly understood. We hypothesized that bromocriptine would have an effect on cognitive functions associated with the prefrontal cortex via its effects on cortical dopamine receptors and on subcortical receptors in areas that project to the neocortex. We found that the effect of bromocriptine on young normal subjects depended on the subjects' working memory capacity. High-capacity subjects performed more poorly on the drug, while low-capacity subjects improved. These results demonstrate an empirical link between a dopamine-mediated working memory system and higher cognitive function in humans.