Research provides insight into how cats purr
The discovery questions a previous theory that cats need neural input to purr.
A new study has revealed that cats purr by producing a vocal fry, similar to a human’s croaky voice, from their larynx without cyclic muscle contractions.
This discovery questions a previous theory that cats need constant neural input to do cyclic muscle contractions and relaxation to purr.
The research, led by Dr Christian T. Herbst of the University of Vienna, involved an anatomical study of cats’ vocal chords to find out how they produced their iconic purring sound. The investigation saw the researchers dissect the larynges of eight domestic cats which had been euthanised due to terminal disease.
Previous theories have suggested that cats vocalise in a vastly different way to other mammals, involving neural patterns to use active muscle contractions (AMCs) of their intrinsic laryngeal muscles to modulate respiratory airflow.
However, this new study has found that a low-frequency phonation, similar to purring, could be drawn from the larynges without any muscle contractions or neural input.
The vocal chords used low-frequency vocal fold vibrations in a way that is similar to the ‘vocal fry’ that humans are able to produce. This is combined with pads in cats’ vocal folds, a little-studied anatomical specialisation, which allow the purrs to be released using the same aerodynamic mechanisms that produce vocalisations such as meows, trills, and screams.
Using this method, the scientists were able to generate vibrations and sound at the same frequency of a domestic cat’s purr, without any neural input at all, from all eight of the extracted larynges. In each of the larynxes, the long duration of vocal fold contact was comparable to the vocal fry phonation of humans.
Although this discovery doesn’t completely disprove the AMC theory, it does suggest that more research is needed to understand exactly how cats purr.
Dr Herbst said: “Anatomical investigations revealed a unique ‘pad’ within the cats’ vocal folds that may explain how such a small animal, weighing only a few kilograms, can regularly produce sounds at those incredibly low frequencies (20-30 Hz, or cycles per second) – far below even than lowest bass sounds produced by human voices.”
The full study can be found in the journal Current Biology.
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