Question: Thanks for answering my last question! You mentioned in your reply that you are carrying out experiments on mice, and the bacteria that grows in their gut, but how would you know if a mouse is sad/happy/feeling emotional in any other way?

Ciarán O'Brien answered on 14 Nov 2014:

There are a couple of basic signs you can use to tell how a mouse is feeling. If they’re scared or unhappy, you’ll find they poop a bit more than usual, or are very jumpy. If they’re happy or feeling courageous, they’ll be more curious and investigate things that a sad or scared mouse would hide from.

Here are some behavioral experiments you can do with mice to see how they’re feeling. There are more, but let’s keep this answer short 🙂

One experiment is to put a mouse in a well-lit circular box with no shadows. Mice prefer to hide away when they’re nervous so you can tell a lot about how well they cope when they’ve nothing to hide behind. If the mouse wanders away from the walls and into the middle of the box it’s a sign that they’re not worried about much.

Another is to put the mouse on a cross-shaped beam above the ground. One pair of the beams has walls either side, and the other doesn’t. Scientists measure the amount of time the mouse spends exploring the beams with walls compared to the beams with a drop on either side to figure out how nervous or (if they’re spending equal time on the beams with no walls) happy they are.

Another one is to put a mouse in a cage with different rooms for a while, to let him get used to it, and then add a new object or a new mouse in one of the rooms, and measure how long he spends interacting with this new visitor. Happy mice usually socialise with each other, so if the mouse you’re studying spends little or no time with other mice, he’s sad or worried about something.

hope that helps! 🙂