Catecholamines and the covert orientation of attention in humans.

The role of brain catecholamines in covert orienting was tested in normal subjects using a cued reaction time paradigm which measures the directional engagement, disengagement and movement of attention. Droperidol and clonidine were administered intravenously to suppress central dopamine and noradrenaline transmission. Both drugs produced reductions in the cost of invalid cueing without change in the benefit of valid cueing suggesting that both noradrenaline and dopamine are involved in facilitating the disengagement of attention. These results are relevant to the slowed disengagement observed with parietal lesions in monkeys and humans since this region of the cortex associated with visuospatial analysis receives a dense innervation by both dopamine and noradrenaline projections in primates.