NEUROPHARMACOLOGY OF TIMING AND TIME PERCEPTION

Time is a guiding force in the behavior of all organisms. For both a r at in an experimental setting (e.g. Skinner box) trying to predict whe n reinforcement will be delivered and a human in a restaurant waiting for his dinner to be served an accurate perception of time is an impor tant determinant of behavior. Recent research has used a combination o f pharmacological and behavioral manipulations to gain a fuller unders tanding of how temporal information is processed. A psychological mode l of duration discrimination that differentiates the speed of an inter nal clock used for the registration of current sensory input from the speed of the memory-storage process used for the representation of the durations of prior stimulus events has proven useful in integrating t hese findings. Current pharmacological research suggests that differen t stages of temporal processing may involve separate brain regions and be modified by different neurotransmitter systems. For example, the i nternal clock used to time durations in the seconds-to-minutes range a ppears linked to dopamine (DA) function in the basal ganglia, while te mporal memory and attentional mechanisms appear linked to acetylcholin e (ACh) function in the frontal cortex. These two systems are connecte d by frontal-striatal loops, thus allowing for the completion of the t iming sequences involved in duration discrimination.