watermaze.org: the friendly field guide to the Morris water maze

The probe trial

Is the probe trial always a test of memory?

Take the platform away and watch what happens. It sounds like the cleanest test of spatial memory there is. But back in 1999 Dr Roger Morris pointed out that rats and mice don't play by the same rules. A rat trawls back and forth over the spot where the platform used to be. Many mice swim to the old spot, head back to where they were put in, return, and then some simply float by the side.

So when a mutant group "fails" the probe, is that poor memory or a different survival strategy? His short essay is here word for word, with a plain-words guide alongside.

Start here

New to the water maze?

What the maze is, where it came from (there is more than one Morris!) and how to plan your first experiment.

Pool & room

How big should the pool be?

The original notes say about 1.8 m for rats with a 10 cm platform, and 1 to 1.5 m for mice with a 5 to 10 cm platform. Here's why size matters.

Where do the cues go?

Out of the pool, around the room, and at least three of them. Plus the cues you didn't mean to give: the camera, the lights and you.

Mice vs rats

Mouse hints from Dr Roger Morris

Mice are not small rats. Mesh platforms, water temperature, time on the platform, and getting them used to being handled.

Protocols

How many trials a day?

The 1998 mouse notes found two trials a day nearly as good as four. How to plan trials, intervals and probe days.

Measures

Which measure should I report?

Escape latency is the classic, but it mixes memory with swim speed. Path length, heading angle, Gallagher proximity and search strategies each tell you something different.

Statistics

Which probe measure is most sensitive?

Maei and colleagues (2009) compared quadrant and zone occupancy, platform crossings and proximity to the old platform. What they found, and what it means for you.

Troubleshooting

My animals float, or hug the wall. Now what?

Floating, thigmotaxis and flat learning curves: what they can mean, and what to check first.

Variants

Barnes, Atlantis, radial arms and human VR

The water maze has relatives. When a dry maze, a rising platform or a virtual pool is the better choice.