It was once thought that cats purred through cyclic contractions of their vocal cord muscles, but a recent study suggests that cats don't need this contraction. Anatomical research has found that cats have a unique padding in their vocal cords that allows them to produce low-frequency sounds, raising questions about our current understanding of cat snoring. Cats' larynxes can produce purring sounds without periodic neural input.
Cats are animals that make many sounds: they meow, scream, and snore. Meows and screams are nothing special from a vocal standpoint. Their sounds are produced in the cat's larynx, or "voice box," much like the vocalizations of humans and many other mammals.
In contrast, cats' purring has long been thought to be special. Research half a century ago showed that cats' purring is produced through a special mechanism - through the periodic contraction and relaxation of the vocal cord muscles in the larynx, which requires continuous neural input and control from the brain.
A new study led by Christian T. Herbst, a voice scientist at the University of Vienna in Austria, shows that these periodic muscle contractions are not required for cats to purr.
Data from a controlled laboratory experiment show that domestic cats are able to produce an impressive, low-pitched purr without any periodic neural input or repetitive muscle contractions in their larynx. The observed vocalization mechanism is strikingly similar to the human "crunch" or "vocal tremor."
"Anatomical studies have revealed that cats have a unique 'pad' within their vocal cords, which may explain why such a small animal weighing only a few kilograms can regularly produce sounds at incredibly low frequencies (20-30 hertz, or cycles per second) - well below even the lowest bass produced by the human voice," Herbst said.
The findings of this study, while not completely overturning previous theories, clearly indicate that the current understanding of cat purring is incomplete and requires further research.