Amphetamine and the adenosine A2A antagonist KW-6002 enhance the effects of conditional temporal probability of a stimulus in rats

As the length of foreperiod preceding an imperative signal increases, reaction time decreases and anticipatory (prior to the signal) responding increases. The authors designed a task to dissociate the effect of elapsing time in the foreperiod and conditional temporal probability of the imperative stimulus. The effects of 2 drugs-amphetamine and KW-6002-known to enhance the effect of foreperiod were compared. Three groups of rats were trained to respond to an auditory signal presented at I of 3 foreperiods, unpredictable from trial to trial. The length of preparation time was different for each group, but conditional temporal probability was the same. Reaction times were faster as a function of increased preparation time, whereas anticipatory responses were strongly modulated by conditional probability. Both amphetamine and KW-6002 speeded reaction times and increased anticipatory responding. The pattern of behavior was consistent with the suggestion that they enhanced the motor preparatory effects of conditional probability rather than speeded a timing process. The authors concluded that preparation time and expectancy (conditional temporal probability of an imperative signal) have differential effects on performance and that amphetamine and KW-6002 enhance the effect of expectancy.