Increasing the speed of an internal clock: The effects of nicotine on interval timing

Abstract

This experiment assessed the effects of nicotine on the ability of rats to time short intervals. Ten rats were trained to discriminate 20 and 60 s signals and were then tested using the peak-interval timing procedure for their ability to reproduce these intervals. Testing continued for 33 days on a weekly schedule in which five saline-injection days were followed by two nicotine-injection days. When they were administered 0.2 mg/kg nicotine on the first day after saline, the rats showed a proportional leftward shift in their timing functions. When the rats were given nicotine again on the subsequent day, their timing functions renormalized. On the following saline-injection day, the rats' timing functions showed a rebound in the opposite direction. This pattern of data implies that nicotine is speeding up the internal clock. Nicotinic interactions with the nigrostriatal dopamine system suggest a possible physiological mechanism for the observed increase in clock speed.