DIFFERENTIAL-EFFECTS OF CLONIDINE, HALOPERIDOL, DIAZEPAM AND TRYPTOPHAN DEPLETION ON FOCUSED ATTENTION AND ATTENTIONAL SEARCH

As the catecholamines have long been implicated in attentional process es, the present investigation compared the effects of the mixed alpha( 1)/alpha(2) adrenoceptor agonist clonidine (CLO), the benzodiazepine d iazepam (DZP), the D-1/D-2 antagonist haloperidol (HAL) and a low-tryp tophan drink (Lo-TRP) on performance of tests of selective attention w ith distracters in four groups of young, healthy volunteers, Using a p lacebo-controlled, cross-over design, selective and dissociable effect s on performance were found with each pharmacological manipulation, Sp ecifically, CLO acted to broaden the focus of attention, HAL generally slowed reaction times during attentional search, and DZP and Lo-TRP p roduced differential effects on stimulus-response compatibility during attentional search. Furthermore, these results underline the usefulne ss of employing a single test with several neurochemical manipulations , allowing for a comprehensive analysis of the neurochemical basis of attention.