CLONIDINE AND DIAZEPAM HAVE DIFFERENTIAL-EFFECTS ON TESTS OF ATTENTION AND LEARNING

The noradrenergic system has repeatedly been implicated in the mediati on of attentional processes. Using a double-blind placebo-controlled d esign, the present investigation examines the effects of two doses (1. 5 mu g/kg and 2.5 mu g/kg) of the alpha(2) adreno ceptor agonist cloni dine (CLO) on performance of various computerised tests of attention a nd learning in healthy, young volunteers. These are compared to the ef fects produced by two doses (5 mg and 10 mg) of diazepam (DZP) on larg ely the same set of neuropsychological tests in a comparable set of su bjects. Both doses of CLO were found to impair performance of the RVIP test of sustained attention, while the higher dose alone improved vis uo-spatial learning. Conversely, the higher dose of DZP produced profo und deficits on visuo-spatial learning, and impaired attentional set-s hifting. This study suggests a role for the alpha(2) adrenoceptor in s elective attention, and for the benzodiazepine receptor in specific co gnitive processes mediated by discrete cortical regions.