Figure 1.

Radial-arm water maze (RWM). Depiction of the RWM with eight arms radiating from a central hub. One arm is always the start, and hidden platforms are located in each of the remaining seven arms at the start of a new session/day (not depicted). After each hidden platform is found, the rat remains on it for 10 seconds and is then placed in a holding cage while that platform is removed. For trial 2, the animal is placed back in the start arm and allowed to freely choose once again. Unlike the appetitive radial-arm maze, in which the animal has no incentive to return to the last arm visited, in the RWM the animal is reinforced to revisit the arm it just found because it escaped at that location on the previous trial. This creates an initial increase in errors in the water version until the rat learns a win-switch or nonmatching to sample rule to not return to the previously visited arm. In this drawing, there are T-shaped structures attached to the floor so the maze may be used in a different configuration by insertion of a structure that rests against these T-shaped guides that are not relevant to the maze's use as a RWM because the T-guides are far below the water level. Drawing courtesy of AB Plastics, Cincinnati, Ohio; reproduced with permission.