AGE-ASSOCIATED IMPAIRMENTS IN A TEST OF ATTENTION - EVIDENCE FOR INVOLVEMENT OF CHOLINERGIC SYSTEMS

We trained three groups of rats, young (Y; 3 months at the start of st udy), middle aged (MA; 15 months), and aged (AG; 22 months), in the se rial five-choice serial reaction time task, a test of attention. There were clear age-related differences in task acquisition: Y acquired th e task quicker than MA rats, which learned faster than AG rats. A subg roup of AG rats [AG(I)] could not reach criterion (> 80% correct, < 20 % omissions under standard conditions of 0.5 sec stimulus duration, 5 sec limited hold). Accordingly, they were tested under conditions of 1 sec stimulus duration. Having acquired the task, under standard condi tions both MA and AG groups were slower to make a correct response but not to collect the food reward. Furthermore, parameter changes, parti cularly reductions in stimulus duration and intensity, revealed furthe r age-related changes in accuracy. Following completion of these studi es, animals were trained in a simpler one-choice task. Importantly, re ducing stimulus duration/intensity in this task revealed no difference s between Y and MA/AG groups, although AG(I) rats were impaired. This dissociation between MA/AG impairments in the one- and five-choice tas k suggests that these animals may show attentional deficits compared w ith Y rats, which are independant of changes in sensory (visual), moto r function, or motivation. Finally, the MA deficit in attention was pa rtially reversed by tacrine pretreatment (3 mg/kg). Also scopolamine ( 0.01-0.075 mg/kg) and mecamylamine (0.3-5 mg/kg) pretreatment impaired choice accuracy of MA but not Y rats, Taken together, the drug studie s imply that the attentional deficits may at least be partially due to changes in cholinergic function.