How do cats produce the low growl that is typical of purring? Other animals capable of emitting these types of sounds are generally much larger and have large vocal cords… Hypotheses have been proposed in the past, but the study was published on October 3rd Current Biology lifts the veil of this mystery even further.
“Scientists explain that cats’ vocal cords have ‘cushions’ of connective tissue that give them an extra layer that allows them to vibrate at low frequencies, they report.” Science. In addition, the larynx of these animals apparently does not need a signal from the brain to purr.”
For this study, researchers analyzed the larynxes of eight domestic cats with the consent of their owners. These cartilaginous organs, where the vocal cords are located, were removed from animals (euthanized in the final stages of a terminal illness) and isolated to ensure that any sound produced was not associated with muscle contraction and that the brain was not affected.
The researchers blew air into the larynx and, to their amazement, these eight organs all produced self-sustaining vibrations at frequencies typical of cat purrs. No muscle contraction was required. The sounds were made possible by these “pads” that lowered the frequency of the sounds produced by the vocal cords.
Calming mechanism
These connective tissues had already been observed, but no one had yet linked them to purring. This new experiment therefore suggests that purring is a passive phenomenon. For Karen McComb, an ethologist specializing in animal cognition at the University of Sussex who was not involved in the study, this explanation fits “much better with what we know about how other vertebrates produce sounds.”
However, not everyone is convinced of this. David Rice, a biomechanist at Tulane University who has worked on the mechanics of cat purring, believes in an interview with the journal that this experiment does not guarantee that the vocal cords of living animals behave in the same way.
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