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Cats are mysterious creatures. There are many things we don’t understand about them. Why do they sleep on our heads? Why do they almost always land on their feet? Why do they do it? love boxes a lot?
However, a cat mystery may have been solved. A team of European researchers say they have found an answer to the question – how do cats purr – that has baffled science and owners for decades.
How do cats purr?
Cats have an amazing vocal range, from high-pitched howls and squeals to deep, resonant purrs. Most of these sounds are well understood, but purring has always been a mystery. The vocal cords (also known as vocal cords) are the bands of muscles in the larynx that allow us to produce sound.
Sounds are produced when air passes through these folds, causing them to vibrate. Low-frequency sounds are produced when the vocal cords are longer, so larger animals with longer vocal cords can make deeper sounds. How relatively small domestic cats handle low-frequency purring has long puzzled scientists.
Until recently, the most accepted idea was that cats purred by alternately contracting and relaxing their vocal cords between 20 and 30 times per second, a process that would be impossible without neuromuscular activity. This explanation, called the active muscle contraction hypothesis or AMC, is based on measuring the electrical activity of cats’ laryngeal muscles while they purr.
Read more: Why do cats always land on their feet?
Test how a cat purrs
However, a recent study directed by Austrian voice scientist Christian T. Herbst and published in Current biology discovered that the process is much more passive. Continuous involvement of the brain is not necessary. Herbst and his colleagues removed the larynxes of cats that had been humanely euthanized due to terminal illnesses. (The cat owners gave consent for their pets’ bodies to be used in this research.)
The researchers mounted each larynx in a tube that supplied heat and humidified air. In a lovely detail not often seen in scientific studies (but I suspect it might be happening more often than scientists mention in their published papers), the researchers used a structure made of LEGO blocks to stabilize the larynx. They then pumped warm, humidified air through the vocal cords. All eight larynxes produced self-sustained oscillations in the frequency range of 25 to 30 Hz, typical frequencies of cat purring. In short, the cats’ larynxes “purred” even without any active neural control.
(Credit: Impact Photography/Shutterstock)
Read more: 7 Fascinating Wild Felines That Might Make You a Cat Lover
Results: muscle contractions of cat purring
These results definitely called into question the AMC hypothesis, although the researchers are careful to note that these findings do not rule out the possibility that there are active muscle contractions involved when live cats purr; instead, they show that purring can occur without them, so it’s a good idea to revisit the AMC hypothesis.
LEGO blocks notwithstanding, these results do not explain as the process works without neurological involvement. However, the researchers proposed a possibility based on a unique anatomical feature of cats.
How do cats really purr?
Cats have layers of fatty tissue, called “pads,” that extend along the inner edge of their vocal cords. While the researchers don’t know for sure if this is the mechanism involved, they say it’s possible that the pads increase the density of the vocal folds, making them vibrate more slowly, thus allowing them to produce a lower tone even though the folds are relatively short.
Researchers say this is no different than “fried voice” in humans (sometimes called “squeaky voice”), a low, grating sound caused by slow vibrations of the vocal cords (and which, for unknown reasons drives some people crazy).
Now if only someone could figure out what cats look at when they look at a wall.
Read more: 5 cats that were owned by famous scientists
