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.