Troubleshooting
Floating, jumping and wall-hugging
Mice can float and jump. Rats generally just swim. Here's what helps.
The original editor's notes put the difference neatly: rats "don't have the option to float or jump", while mice "do have the option to stop swimming and just float, and to jump". Here's what the original notes suggest for each problem, with links to the full text.
Floating
- Make sure the water isn't too cold. In Dr Roger Morris's experience, lowering the temperature by 2 °C and his mice "went on strike" (time and intervals).
- Get mice used to handling and to simple, unthreatening tasks before the water maze. The 1999 essay suggests this minimises thigmotaxis and passive floating (the essay).
- Measure it, so you know whether a poor score is about floating (inactivity).
Jumping
- Mice "do leap", so the pool needs to be high-sided enough to stop them leaping out (time on platform and rescue).
- Step back as they climb onto the platform, and try to keep them there for 10 seconds.
Swimming round the wall
- Some wall-swimming is normal in early trials (learning to find the platform).
- Make sure the platform isn't so close to the wall that circling finds it (the pool).
- See thigmotaxis for how to measure it.
Not learning at all
- Check they can see the cues from near the platform (size of pool and platform).
- Check the cues are far enough away to need spatial analysis, but visible to a swimming mouse (cues for mice).
- Don't leave them swimming unsuccessfully for too long at first, or "they will associate the swim with failure & panic".
- Run a cued, visible-platform phase to rule out problems with vision or motivation (cued and hidden).
For telling floating from searching, see floating or inactivity in Morris water maze analysis.
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