EFFECT OF SCOPOLAMINE ON VISUAL-ATTENTION IN RATS

In the present study, the effects of scopelamine (SCOP) were determine d upon the performance of rats in the five-choice serial reaction time task, a test of attention analogous to the continuous performance tes t in man. Rats were trained to detect and respond to brief flashes of light presented randomly in one of five locations until a stable level of performance was reached. SCOP (0.03-0.1 mg/kg SC) was administered 30 min prior to testing under standard conditions of stimulus present ation. SCOP reduced response accuracy at the highest dose and dose-dep endently increased omissions and perseverative responses. However, the se effects were mimicked by scopolamine methylbromide (SCOPMBr) which might suggest a peripheral site of action. When the task difficulty wa s increased by manipulating the stimulus presentation parameters, i.e. reduced stimulus intensity, duration or temporal predictability, SCOP (0.075 mg/kg SC) failed further to impair performance accuracy. Howev er, in two separate experiments, SCOP (0.075 mg/kg SC) robustly increa sed the distractibility caused by a burst of loud white-noise occurrin g unpredictably during the intertrial-interval: SCOP significantly dec reased accuracy and increased omissions, magazine latency, premature a nd perseverative responses compared with vehicle and the equivalent do se of SCOPMBr. These findings provide further evidence of a role for t he central cholinergic system in attention.