Catecholamines and attention. II: Pharmacological studies in normal humans.

Part I of this review [17] found evidence from animal and clinical studies of a role for catecholamines in the control of attention. This part of the review examines the results of a systematic study of the acute effects of a number of catecholamine active drugs on measures of attention in normal adults. The results are interpreted within the context of a general capacity model of information processing in which level of arousal determines the capacity to process stimulus information and level of activation the capacity for processing response demands. Whilst the dopamine antagonist, droperidol, and the alpha agonist, clonidine, had similar effects on behavioural indices of processing capacity and reports of the degree of effort required to carry out processing, they differentially affected subjective state and measures of activation and arousal. These differences provide some support for the hypothesis that central noradrenaline and dopamine modulate the capacity for early and late processing of information, respectively, in humans.