Not All Rats Like to Be Tickled the Same Way: New Study Reveals Sex Differences in Play
For years, scientists have used tickling as a primary tool to study animal happiness. By mimicking the natural social interactions of rats, researchers hoped to create a standardized way to measure positive emotions. However, a new study suggests that a “one size fits all” approach to play may be overlooking critical differences in how male and female rats experience joy.
Research led by Vincent Bombail, an animal behavior researcher at Scotland’s Rural College in Edinburgh, reveals that female rats have a distinct preference for gentler, more playful interactions compared to their male counterparts. The findings, published April 15 in Biology Letters, suggest that the same physical experience can evoke entirely different emotional responses depending on the individual.
The Flaw in the Standard Tickling Protocol
To understand these differences, it’s important to look at how scientists have traditionally “tickled” rats. Since the 1990s, the standard protocol has involved a researcher flipping a rat onto its back, pinning it, and tickling its belly. This method was specifically designed to mimic the “rough-and-tumble” play typically observed among young male rats.
While this approach worked for some, Bombail noticed significant variations in how different rats reacted. This led his team to question whether the pinning process—a dominant physical move—was actually enjoyable for all animals, or if it was merely tolerated by some while being disliked by others.
How the Study Measured Happiness
To determine what rats actually prefer, the researchers used an “affective bias test.” Instead of relying solely on physical reactions, they measured the rats’ emotional states through their associations with rewards. The experiment was broken down into three scenarios:
- High-pinning tickling: The standard, more vigorous protocol.
- Low-pinning tickling: A gentler approach where rats could chase and be chased by the researcher’s hand, spending significantly less time pinned.
- Control: No interaction with the researcher.
Immediately after each session, the rats dug through different materials—such as ribbons, cardboard, or felt—to find a buried treat. The logic is simple: if a rat feels happy after a tickle session, it forms a positive association with the material used during that session. By observing which materials the rats chose to dig through in subsequent trials, the researchers could “ask” the animals which experience they preferred.
The Results: Males vs. Females
The data revealed a stark contrast in preferences based on sex:
- Male Rats: Males enjoyed both the high-pinning and low-pinning treatments equally. They chose materials paired with either form of tickling far more often than the control material.
- Female Rats: Females showed a strong preference for the low-pinning, playful protocol. While they liked high-pinning slightly more than no interaction at all, they overwhelmingly preferred the gentler approach.
Bombail notes that these results mirror natural behaviors. In the wild, young male rats tend to be more physical and rough, while female play involves more running and escaping.
Why This Matters for Animal Welfare
This discovery has significant implications for how science approaches animal welfare. For decades, research focused on minimizing negative experiences, such as stress and pain. This study shifts the focus toward enhancing positive mental states.
“This research helps us understand these animals as playful but also rich and complex and having opinions,” says Daniel Weary, an animal welfare scientist at the University of British Columbia. Weary emphasizes that understanding the affective lives of animals remains one of the most challenging and fascinating questions in modern science.
Looking Toward the Biology of Joy
The scientific community has a deep understanding of the biology of stress—how it affects hormones, the immune system, and the gut microbiome. Bombail’s next goal is to apply that same rigor to the other side of the spectrum. He plans to explore the physiology of positive emotions to understand the actual biology of “feeling good.”
Key Takeaways: Rat Play Preferences
- Sex Matters: Female rats prefer gentler, low-pinning play; male rats enjoy both vigorous and gentle play.
- Protocol Shift: The standard “pin-and-tickle” method mimics male play and may not be the ideal way to promote positive welfare in females.
- Affective Bias: Researchers used treat-association tests to objectively measure the rats’ emotional preferences.
- Welfare Goal: The study highlights the importance of tailoring welfare interventions to the specific needs and sex of the animal.
Frequently Asked Questions
Do all rats enjoy being tickled?
While most rats experience positive affective states when tickled, the type of tickling they enjoy varies. Females, in particular, prefer a more playful, less restrictive experience over the traditional pinning method.
What is an affective bias test?
An affective bias test is a method used to determine an animal’s emotional state by seeing how they associate a stimulus (like tickling) with a reward (like a treat). If the animal prefers the reward associated with a specific activity, it indicates a positive emotional response to that activity.
How does this change animal research?
This research encourages scientists to consider sex differences when designing welfare interventions and study protocols. It suggests that to truly measure “happiness” in animals, researchers must account for individual and sex-based preferences rather than relying on a single standardized protocol.