Amphetamine and memory for event duration in rats and pigeons: Disruption of attention to temporal samples rather than changes in the speed of the internal clock

Abstract

In Experiment 1, pigeons were trained to match short (2-sec) and long (8-sec) sample durations to red and green comparison stimuli and red and green samples to vertical and horizontal line comparisons. They received injections of d-amphetamine (2.0 mg/kg) or saline, and the delay interval was manipulated (0, 1, 3, and 9 sec). In Experiment 2, rats were trained to discriminate short (2-sec) or long (12-sec) durations of either houselight illumination (light group) or tone (tone group), using a choice procedure. During the test phase of each trial, the left and right levers were presented with the cuelight above one of them on (cued lever) while the other was off (uncued lever). For some of the rats, the correct response following the short sample was to press the cued lever, whereas following the long sample, it was to press the uncued lever. This was reversed for the remaining rats. The rats received injections of methamphetamine (1.5 mg/kg) or saline, and the delay interval was manipulated (0, 1, 3, and 9 sec). Memory for color samples in pigeons was not affected by amphetamine. However, for both rats and pigeons, amphetamine reduced the accuracy of event duration memory even at the 0-sec delay but did not increase the slope of the retention functions. In addition, in neither experiment was there any evidence that amphetamine produced an overestimation of perceived sample duration. Amphetamine predominantly affected temporal memory in both pigeons and rats by disrupting attention to temporal samples rather than by simply increasing the speed of the internal clock.