Assessing a vigilance decrement in aged rats: effects of pre-feeding, task manipulation, and psychostimulants

Rationale: In studies assessing sustained attention in humans, performance is often characterised by a decline in function over time. This response pattern, termed the vigilance decrement, is sensitive to manipulations affecting task difficulty, and to reversal with psychostimulant drugs. A valid test of attention in non-human species requires both comparable characteristics of performance, and sensitivity to similar psychoactive drugs. The five-choice serial reaction time task (5-CSRTT) has been described as a test of sustained attention in the rat, however, studies describing vigilance decrements and performance effects of psychostimulants in this task are scarce. Objectives: We manipulated the standard 5-CSRTT to determine under which conditions a replicable vigilance decrement could be observed, and sought to determine whether this pattern of changes was sensitive to psychostimulant administration. Methods: One and two-year-old rats performed in five-choice sessions extended to 250 trials. Task difficulty was manipulated by either increasing or decreasing the duration of stimulus presentation, and pre-feeding studies were performed to control for effects of the additional food earned. In the two-year-old group dose-responses were then derived for nicotine (0.1-0.4 mg/kg), amphetamine (0.05-0.4 mg/kg) and caffeine (3-10 mg/kg). Results: Extending five-choice sessions revealed a decline in the performance of two-year-old rats as a function of trial number. Increasing task difficulty induced a response-decrement in one-year old rats; whilst reducing it enhanced the performance of two-year-old rats to that observed in younger subjects. Pre-feeding did not alter the response patterns observed in either group. Nicotine, amphetamine, and caffeine all reversed the performance decrement observed. Conclusions: These results demonstrate that similar performance characteristics can be observed in both human and rat, serving to validate further the 5-CSRTT as a measure of sustained attention.