Protocols
How long, how many and how often: trials and intervals
Two trials a day can be nearly as good as four. Here's what else the notes say.
How long should a trial last? How many a day? How long between them? The original notes give practical answers, and they differ a little between rats and mice. Here they are side by side, each in its original words.
For rats
The original learning notes suggest lifting the rat out if it hasn't found the platform after about two minutes, and leaving it on the platform for about 15 seconds to look around. Probe trials last 1 to 2 minutes. Read them in full on learning to find the platform and rats can cheat.
For mice
Time & Intervals of Swimming
1. We use 2 mins in a 2m pool with a 15 cm platform. If your pool is as small as 1m, I would swim them for 1 min, & when they fail to find the platform, guide them to it so they climb on. Ideally you leave them there for 10 seconds, so they assess the surroundings. In practice they will make a leap for it if you let them. So as they climb on, step well-back & try to ensure they stay on for 10 seconds. If they immediately take to the water & keep swimming, intervene again to guide them back. They have to learn that rescue is dependent on staying on that platform.
2. If they leap for you before you retreat, you may as well catch them, as at least they have got the idea. You should find that on the first day your mice mostly fail to find the platform. Then on subsequent dates their efforts are greeted with increasing success. If you leave them too long at the beginning, swimming around without success, they will associate the swim with failure & panic.
3. We find that mice given 2 trials per day learn nearly as quickly as 4 times a day. If you are worried about the stamina of elderly mice, cut back to 2 per day. Our mice look forward to their swim (they rattle the tops of their cages when my postdoc comes to collect them). We suspect they possibly enjoy it too much, and extend the swim-time because the alternative is to go back in a boring cage. Then we tried lowering the temperature of the pool by 2 deg, and they went on strike ! What I was leading-up to is that if the mice are not panicking, I suspect the swim is not traumatic, and they enjoy doing laps of the pool.
4. Intervals between swims is important. We use 30 mins, as being a good way to reinforce learning.
Original text: Dr Roger J Morris, 1998, with editor's notes by Richard Baker. Copyright (C) 1998 RJ Morris & HVS Image. Reproduced unchanged. Copyright Richard Baker© 2013. All Rights Reserved.
: The asterisks in the mouse notes are in the original. We haven't found what they referred to.
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