The long-term emotional wellbeing of mice can affect their behavior — and that’s important for researchers using them for models.

To say that lab mice are important to science is a hell of an understatement. Mice have been used in biomedical research for centuries. Entire fields of research wouldn’t even exist without animal models. The humble mouse has proven valuable in everything from genetics to psychology.

But, in recent years, researchers have become more and more aware that there is a problem with lab mice; or rather, several. For instance, there’s almost no diversity in lab mice, which means that the vast majority of studies are carried out on male mice. This has cascading effects on multiple levels, and to put it simply, it means that mouse studies might not be all that representative for women.

Here’s another issue that researchers should no longer ignore: mice’s feelings.

Animals experience a broad range of emotions that are crucial for their decisions, behavior, and biology. For the most part, however, science has largely been uninterested in the positive emotions lab mice can exhibit. That’s a problem, a team of British researchers is saying. If we’d focus a bit more on making them happy, we’d be getting better results in lab tests, according to a new study.

“Our results also demonstrate that repeated negative events can have a cumulative effect to reduce resilience in laboratory animals, which has significant implications for animal welfare,” the authors write.

To test how mice react to negative emotions, researchers… well… gave rats negative emotions. They lifted the mice by the tail when it was time to handle them, a process known to annoy and startle mice. This tail-lifted group was compared with another group that was handled via the less stressful “tunnel handling” technique, where mice hang out in a plastic tube instead of being physically grasped.

When it came to positive stimuli (like being given some sugar water), the two groups responded the same. But when it came to negative stimuli, there were big differences between the two groups.

Lead researcher, Dr. Jasmine Clarkson notes:

“Animals have emotions that are affected by what happens to them in their everyday lives. Like us, they can get anxious and depressed, but how does that change their experiences of the good and the bad things in life? We found that anxious and depressed laboratory mice are more disappointed when something bad happens, but their low mood has no effect on how elated they are when something good happens.”

“So if we apply that to the welfare of our lab animals, it means poor welfare still allows animals to appreciate reward but it makes them less resilient and potentially reduces the reliability of biomedical experiments. These are important findings which emphasize the benefits of the highest level of care that we should adhere to.”

For starters, this suggests that the tunnel handling method should be used more widely, ensuring that handling is the least stressful treatment possible.

But more importantly, it suggests that lab animal welfare and good science go hand in hand — and it’s not a trivial matter. Psychology and medicine are plagued by a replication crisis, and it’s plausible that a part of that problem comes from animal model studies. Researchers are struggling to recreate each other’s findings for reasons that are not clear. For instance, if someone carried out a study handling mice directly, and someone else tried to replicate it using a tunnel, they might get different results.

If something as simple as handling can help address this issue, then it’s definitely something worth addressing; and if it makes the lives of lab mice a bit more pleasant, what’s not to like?

The study was published in Proceedings of the Royal Society B.