A mystery has now been solved: scientists have discovered where purring comes from in cats, a sign that your companion is happy, and how these little cats produce it.
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Purring is produced by “pads” of fibrous tissue embedded in the vocal cords of cats, which vibrate and produce this sound reminiscent of the rumble of an engine, we can read in a study published in early October in the journal Current Biology .
“This could explain how such a small animal, weighing just a few kilograms, can regularly produce sounds at these incredibly low frequencies (20-30 Hz, or cycles per second) – far below the lowest bass tones of human voices,” said Christian Herbst, Lead author of the study conducted at the University of Vienna, in an interview with The Guardian.
A theory from the 70s debunked
Since the 1970s, the scientific community has instead assumed that purring is caused by the contraction and relaxation of the larynx muscles about 30 times per second. This would therefore imply a constant contribution from the brain, a theory that this new study calls into question.
In fact, what would happen in the larynx of cats would be similar to vocal brooding in humans, the researchers conclude. This is the sound that the vocal cords produce when they are squeezed, making their individual vibrations audible when speaking. It is significantly more common, especially among people who speak Vietnamese, Danish and American English.
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To reach their conclusions, the researchers, with the consent of their owners, separated the larynxes of eight domestic cats that had been euthanized after suffering from a terminal illness in order to study them.
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By pinching and directing warm air through the larynx, scientists achieved sounds similar to a purr. This enabled them to see that, contrary to their assumption, neither a laryngeal muscle nor neural input was required.
Uncertainties remain
In an interview with the journal Science, University of Sussex animal behavior expert Karen McComb – who was not involved in the study – stressed that the results “seem much more consistent with what we know about how vocalizations are produced in other vertebrates. “.”
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For his part, David Rice, a biomechanics engineer at Tulane University, expresses some reservations about the methodology, arguing that there is no guarantee that the severed vocal cords will function in the same way as if they were severed in the body of a living cat.
A factor that the first author of the study, Christian Herbst, recognizes. He explains to science that the study of purring would be much more accurate and precise if it were possible to insert probes into the larynx of living cats. However, since cats only purr when they feel safe and happy, this is unlikely.