Play behavior and laughter in rats has a lot to do with their environment and with the part of the brain that controls fight or flight responses.
By Rachel McDermod
While rats may suffer from a bad reputation in popular media, these little rodents have something in common with humans: they are incredibly playful. Play has been observed in many species, yet scientists still know very little about the brain’s role in play behavior or the full scope of play.
Due to their playful natures, rats are excellent animals to observe and gain insight on how play affects brain activity. A new study by researchers from Humboldt University of Berlin and other German facilities pinpoints where in the brain play stems from in rats, and what type of environments are most favorable to play behavior in these animals.
The comfort zone
To engage in play, an animal must feel comfortable and safe, but how much do these feelings change playful behavior? To answer this question, researchers placed the rats used in this study in a low-stress environment for a few days to become comfortable with their surroundings and handlers. Once the rats were accustomed to their environment, the researchers began initiating play with them. As a sort of game, the researchers would stick one of their hands into the rats’ enclosure and quickly move it around, causing the rats to chase the hand in quick bursts of speed. Additionally, researchers would gently tickle the rats on their backs and bellies.
Past research has shown that, when amused, rats make high-pitched noises that can’t be heard by humans but can be documented by sensitive recording devices to indicate if a rat is playing. Recordings from this experiment showed that during the hand-chasing game and tickling the rats emitted these vocalizations, which researchers think are the rat equivalent to laughter.
To test if the rats were playful in less comfortable situations, the rats were also placed in unfamiliar enclosures or in more stressful environments, such as under a bright light, for short periods of time while being tickled. The researchers found that under these conditions, the rats did not laugh or respond in playful behaviors like they did when they were comfortable and free to explore their environment. This supports the hypothesis that play behavior is dependent on an animal’s mood and comfort.
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After demonstrating how the rats’ moods affected their willingness to engage in play, the researchers wanted to take their study further by pinpointing where in a rat’s brain play behavior stems from. Using surgically inserted neural implants, researchers recorded the rats’ brain activity during the experiment and determined which areas of the brain became activated when the rats were being tickled and playing.
Fortunately, the researchers for this study had some idea of where in the brain to focus on. Past studies have indicated that an area in the midbrain called the periaqueductal gray (PAG) may be responsible for play. This area controls vocalizing, the fight-or-flight response, and many instinctual behaviors, all of which are vital to play behavior. Researchers wanted to test the hypothesis that the PAG is responsible for play by blocking this part of the brain using injected substances, and then seeing if the rats still showed playfulness. These substances were muscimol, which is a compound that binds to receptors in the PAG and temporarily shuts off its natural functioning, and lidocaine, which is a numbing chemical. Once they inhibited the PAG, researchers tickled the rats again, but found that the rats showed little indication of a playful response and made less vocalizations.
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The results seen in this experiment support two ideas. Firstly, play behavior mainly occurs when an animal is comfortable and at ease in their environment. Secondly, the PAG is important in play and laughter. The recorded firing of neurons in the PAG during play, and the reduction of this response when this part of the brain was inhibited, indicate that this area of the brain has an important role in playfulness. The topic of play is complex, and researchers posit that the ability to play is reliant on many factors, including the animal’s environment and different parts of their brain working together.
Play behavior moving forward
This study paves an exciting path forward for researching play behavior, and hopefully for unlocking the secrets and intricacies of animal play. Not only can this research be used to learn more about rodent play behavior, but it may lead to similar studies on other species, studies on how age impacts play within a single species, or even studies on whether the PAG recognizes structured play with rules.
A rat might normally be the last animal that a person relates to, but it’s easy to see the parallels between our two species when it comes to play. While the topic of playfulness is still full of questions, humans can benefit from integrating more play into daily life. Take time to make your everyday spaces comfortable and relaxing to allow yourself the freedom of play. Enjoy the little things. Be thankful for a brain that, no matter how mysterious, allows for play and laughter.
This study was published in the peer-reviewed journal Neuron.
Gloveli, N., Simonnet, J., Tang, W., Concha-Miranda, M., Maier, E., Dvorzhak, A., Schmitz, D., & Brecht, M. (2023). Play and tickling responses map to the lateral columns of the rat periaqueductal gray. Neuron, 111, 1–12. https://doi.org/10.1016/j.neuron.2023.06.018
About the Author
Rachel McDermod is a science communicator, keen tidepooler, and playful person. She holds a BS in Marine Biology and is pursuing a MS in Science Communication & Public Engagement. Her biggest passion is igniting curiosity in others. She lives in sunny California with her husband and polka-dotted dog.