Why rats play hide-and-seek and sometimes hide again

When rats play hide-and-seek with humans, being found does not always mean the game is over. In one laboratory experiment, some rats ran away and hid again after the researcher had discovered them, even though finding the rat was supposed to lead to a rewarding playful interaction.

The animals were extending the game and postponing their reward.

A 2019 study published in Science demonstrated that rats could learn a two-role version of hide-and-seek, alternating between finding a human and hiding from one. Three years later, a study in Current Biology examined the brain recordings from these games in greater detail, revealing patterns of neural activity associated with different aspects of play.

Together, these findings offer an unusual window into the behavior of animals more often discussed as laboratory subjects or urban pests.

Found you. Now hide again.

The original experiment took place in a 30-square-meter room fitted with cardboard barriers and several types of hiding places, including transparent and opaque boxes.

There were two players: a rat and a human.

When the rat was the seeker, it entered a small starting box and the lid was closed. The researcher hid somewhere in the room and then opened the box remotely, allowing the rat to begin its search.

In the other version, the roles were reversed. The box remained open, the experimenter stayed nearby, and the rat had to find somewhere to hide.

All six young male rats in the initial group learned to seek within one or two weeks. Five also learned to hide and switch between roles.

The researchers did not offer food rewards.

Instead, a successful round ended with a playful social interaction, including petting or tickling.

That detail matters because food is a standard motivator in animal learning experiments. Here, the reward was the interaction itself.

And yet some rats behaved in a way that complicated the idea that they were simply working toward that reward. After being discovered, they sometimes ran away and hid again, delaying the very interaction they had been trained to expect.

This was consistent with the possibility that the game itself had become rewarding, although the researchers could not conclusively separate the enjoyment of play from the anticipation of social contact.

Different roles, different strategies

The rats did more than memorize where the boxes were.

When searching for a hidden human, they used visual cues and remembered previous hiding locations. If the experimenter repeatedly hid in the same place, the animals became faster at finding that location. When the rat could see where the researcher went, the search was also quicker.

When the animals became hiders, their behavior changed.

They preferred opaque hiding places over transparent ones. Crucially, that preference was not observed in the same way when the rats were seeking.

This distinction made the finding more meaningful than a simple attraction to dark spaces. Their choices varied with the demands of the game.

The animals also changed their vocal behavior.

Rats communicate using ultrasonic calls that humans cannot hear without special recording equipment. Researchers monitored these calls throughout the experiment and compared them with the different phases of play.

The animals often vocalized during active parts of the game, including when they found the human. But when hiding, they produced relatively few calls. When a hiding rat was discovered, it frequently fell silent.

Whether this amounted to an intentional strategy to avoid detection could not be established. But it demonstrated that the rats' behavior was sensitive to the situation and the role they were performing.

Reading the game through brain activity

The 2019 experiment also examined neurons in the medial prefrontal cortex, a brain region involved in organizing flexible, goal-directed behavior and using rules.

The researchers recorded neural activity through implanted electrodes.

Some neurons responded strongly to particular events. Closing the starting box, for example, signaled that the rat would be the seeker. A subset of neurons changed its firing around this cue.

In 2022, Bence Bagi and colleagues returned to the recordings with a different question.

Rather than starting with a list of behavioral events and asking which neurons responded to them, they used a statistical approach to identify recurring patterns in neural activity without first telling the model what the animals were doing.

The main analysis included recordings from four rats across 13 experimental sessions. The researchers recorded between a few and 31 neurons simultaneously, depending on the session.

They used a hidden Markov model, a mathematical method for identifying a sequence of underlying states from observed data.

The software examined patterns of neural activity. Only afterward did the researchers compare the inferred states with the animals' behavior.

The resulting patterns aligned with recognizable parts of the game.

Some corresponded to running and exploring. Others appeared during interactions with the experimenter or when animals moved near the walls and hiding boxes.

One particularly interesting pattern emerged when rats peeked out of boxes. A similar neural state appeared both when they looked out from the starting box and when they peeked from other hiding places.

The analysis thus helped reveal behavioral features directly from neural data, without requiring the researchers to label every relevant action in advance.

The team also examined another previously collected dataset in which rats either played hide-and-seek or watched another rat play.

The patterns of prefrontal activity associated with playing were clearly different from those observed when an animal merely watched.

The 2022 paper was not a new, independent demonstration that rats could learn hide-and-seek. It was a more detailed computational analysis of existing recordings, including data from the earlier experiment.

Can playing be its own reward?

Traditional laboratory tasks often ask animals to perform a simple action in exchange for a predictable reward. Hide-and-seek requires a much more flexible set of behaviors.

The animal must recognize which role it is playing, use information about the other player, choose suitable locations, and adjust its behavior as the situation changes.

The 2019 researchers suggested that the rats might find the activity itself rewarding.

The strongest behavioral clue was the tendency to hide again after being found, delaying a playful interaction in order to prolong the game.

But an animal's internal experience cannot be directly inferred from its movements. The studies do not establish that rats experience hide-and-seek exactly as children do. Nor do they demonstrate a human-like understanding of another individual's thoughts.

Both studies also have limitations. The experiments involved small numbers of laboratory animals, a human partner, prior training, and a particular form of social reward. These factors shaped the conditions under which the behavior emerged.

What the findings do establish is that rats can participate in a surprisingly elaborate role-based game, adjust their strategies to different roles, and display identifiable patterns of prefrontal activity during play.

Such abilities may have deep evolutionary roots. Searching and hiding are useful survival behaviors across many species, although the studies did not show that wild rats naturally play the same kind of game.

The most memorable moment remains remarkably simple.

The human finds the rat. The round could end and the animal could receive its reward.

Instead, the rat sometimes darts away and disappears behind another box.

The game goes on.