The Morris water maze is a standard test for spatial memory in rats. In this test, a rat is placed in a pool with cloudy water. Just below the water surface is a small hidden platform. The rat swims around until it finds and climbs onto this hidden platform, allowing an escape from the water.
Normally, with repeated trials, the rat learns the spatial location of the platform and swims straight to it.
Which of the following can result in enhanced learning (i.e. fewer trials needed) in the rat?