Radial maze in the water tank: an aversively motivated spatial working memory task.

An 8-arm radial maze with 40 X 40 X 12 cm channels was inserted into a circular tank (120 cm in diameter, 60 cm high) filled 30 cm deep with 25 degrees C opaque water. Rats (n = 13) had to escape from the central area of the maze (30 cm in diameter) onto an invisible bench (1 cm below water surface) at the far end of each channel. Twenty sec after each choice the bench was collapsed and the animal was forced to choose again until all 8 channels had been visited. From the very beginning rats performed better than chance. The acquisition and performance of this aversively motivated radial maze test is similar as in conventional elevated 8-arm radial mazes.