Scientists finally uncover the secret behind cats’ adorable purrs — and it’s surprisingly similar to a pop star’s vocal trick
A cat’s purr, the mysterious sound every feline produces when they are believed to be happy and content, is similar to a vocal technique applied by many pop stars like Katy Perry and Britney Spears. As it became the subject of a research study, scientists delved into a cat’s anatomy and discovered a detail that previous research may have missed. While the world grooved to hit music made by pop stars, it turns out, our feline friends have been doing it all along. A study published in the journal Current Biology explains how cats generate the purring sound using a method similar to humans.
Humans love the calming energy of a cat’s purr, which often soothes them. Usually, the purring sound indicates that the cat is happy or relaxed. However, the incredibly low frequency of the purrs intrigued scientists as they tried to figure out how cats, relatively smaller animals, were equipped to generate such low frequencies. While other animals make similar sounds by contracting and relaxing the muscles in their voice box, or larynx, cats barely require any neural stimulation to do the same. Christian T. Herbst, an Austrian voice scientist at the University of Vienna and co-author of the paper, revealed that cats have a “unique ‘pad’ within their vocal folds” that allows them to produce sounds ranging from 20 to 30 Hz or cycles per second.
This is “far below even than the lowest bass sounds produced by human voices," the co-author said in a statement to Phys.org. While other cat sounds like meows and screeches are generated from the larynx, the study found purrs to be an exception. "From the viewpoint of neural control, electrical brain stimulation results in a clear distinction between purrs and other cat vocalizations, such as meows, growls, and hisses," the paper stated. Despite previous findings about all cat sounds emanating from the voice box, the researchers carved a path of their own by reassessing a cat’s larynx.
An experiment on the voice boxes of eight cats that were euthanized due to terminal disease revealed that passive aerodynamic behavior of the voice box produced the low-frequency purrs. The study explained, "These low-frequency vocal fold vibrations involve a special vocal mode with an unusually long closed quotient, reminiscent of the ‘vocal fry’ register in humans.” The macroscopically visible “pads” are likely responsible for the sounds. They run along the vocal fold's edge and are made of star-shaped cells, myxoid tissue, vessels, sparse collagen, and elastin fibers that increase the voice box's density, allowing slow vibrations that produce purrs. The pads are independent of the age and sex of cats.
On a less scientific note, Kelly Morgan, DVM, clinical instructor at the Chicago Center for Veterinary Medicine at the University of Illinois, equates purring in cats to smiling in humans. It does not always confirm happiness, but may also occur during stressful situations. “People will smile when they’re nervous, when they want something, and when they’re happy, so perhaps the purr can also be an appeasing gesture,” she said, per WebMd.