Novel object recognition test

The question

Here's a puzzle worth a few minutes: How do we know a mouse remembers an object it saw yesterday? You're watching Morris Water Maze Software Guide, over at morriswatermazesoftware.com.

Meet the novel object recognition test

The novel object recognition test uses a natural preference: rodents tend to explore new things more than familiar ones. The animal explores two identical objects, then after a delay, one object is swapped for a new one. More time with the new object means it remembers the old one.

How it runs

Here's the routine, in order. First, habituate the animal to the empty arena. Next, run a sample phase with two identical objects. Then, after a set delay, replace one object with a novel one. Finally, score exploration, usually the nose close to and pointing at an object.

Strengths and limits

What's it good for? No food restriction or punishment. The delay can be set to test short or long-term memory. It suits large test batteries. Now, the small print. Objects must be equally interesting and impossible to climb or move. Low exploration makes scores unreliable.

What to measure

Now for the numbers, my favourite bit. Discrimination index: novel minus familiar exploration time, divided by the total. Total exploration time: a check on motivation and activity. Nose-point zones around each object: a precise, automatic way to score exploration. Time slices: preference often fades as the new object becomes familiar. A mouse with a discrimination index near zero might have forgotten. But if it barely explored anything, the score is just noise. Total exploration time tells you which.

The takeaway

If you remember only one thing, make it this: total exploration time and its neighbours tell you how the task was done, not just how fast. Everything we covered is written up below.