The science behind playful behavior: Tickling rats reveals the role of the brain

Playful behavior is not unique to humans: it is found in a variety of animals, including birds, bees, monkeys, marsupials, lizards, turtles, crocodiles, and even fish. A recent study of the “rough and rowdy” play of young rats further supports the idea that social fun is instinctual in mammals, and possibly in other species as well. Researchers from Germany conducted experiments in which they tickled and chased rats around an open cage and noticed that a certain part of the rats’ brains, called the periaqueductal gray matter (PAG), was very active during these playful interactions.

The PAG is a region of the midbrain that is present in mammals, reptiles, fish and insects, making it one of the oldest and most preserved parts of the animal brain. It is known to be involved in responses to pain and other threats and is closely associated with animal vocalizations. In the study, the lateral column of the PAG was artificially suppressed in adolescent rats, and they squeaked less when tickled on their stomachs and backs. In addition, these inhibited rats were less likely to playfully chase a human hand around the cage.

Neuroscientist Michael Brecht of Humboldt University Berlin explains that vocalizations like laughter are crucial for play and are indicative of regulated brain behavior. He compares this to children who check for laughter during a fight and stop if their mate is no longer laughing. Although rats don’t laugh like humans, they emit a high-pitched squeak when they are amused. Previous research has shown that the more ticklish a rat is, the more playful it is, making it an ideal model for studying animal play.

Brecht and his colleagues have been studying tickling in rats for several years, but are just beginning to uncover its specifics. The behavioral changes observed in recent experiments strongly suggest that PAG neurons are involved in play. The researchers note that a properly functioning PAG is essential for play and tickling. Interestingly, when rats were placed in a novel stressful environment, they showed a lower propensity to play, indicating that the PAG may be focused on play behavior only when it is not engaged in the immediate escape-fight response.

The brain axis for tickle play likely includes the PAG and other brain regions associated with memory, emotion, sensory responses, and decision making. However, understanding the neural mechanisms controlling PAG play is still at an early stage. The researchers emphasize that it is still unclear how play is implemented in these neural circuits and call for further research to find out whether the PAG plays a similar role in play in other animal species and whether this brain region can become stronger after brief bouts of fun.

The study, published in the journal Neuron, sheds light on the role of the brain in play behavior and provides valuable insight into the neural mechanisms underlying play in animals.

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