06.11.2023: Domestic cats use a variety of sounds to communicate with their environment. The classic purring sounds, however, are actually quite unusual. Cat purring has been assumed to be produced by cyclic contractions of the laryngeal muscles, centrally controlled by the brain. An international study that was recently published in Current Biology with the participation of the University of Veterinary Medicine Vienna now shows that cat larynges can produce purring sounds even with no neural input. This suggests that the dynamics of cat purring are more complex than had been previously believed.
Most mammals produce vocal sounds through the self-sustained oscillation of laryngeal tissues according to the so-called myoelastic-aerodynamic (MEAD) principle. In contrast, domestic cats (Felis silvestris catus) have long been believed to produce their low-frequency purr vocalisations through a radically different mechanism involving neurally driven active muscle contractions (AMCs) in the larynx, typically at a frequency between 20 and 30 Hz. This value is far below the lowest tones that humans can produce with their voice. Direct empirical evidence for this AMC mechanism, however, is sparse.
Research team tests the AMC hypothesis …
The researchers conducted a laboratory experiment using excised larynges from domestic cats to test the prediction of the AMC hypothesis that vibrations should be impossible without neuromuscular activity and therefore unattainable in an experimental set-up with excised larynges.
… and partially rejects it
Surprisingly, the excised larynges produced self-sustained oscillations at the typical purring frequency for cats. A histological analysis of the cat larynges revealed the presence of connective cushion like structures up to 4 mm in diameter embedded in the vocal fold. This vocal fold specialisation appears to allow such small animals to produce the unusually low fundamental frequency values observed in purring.
“While our data do not fully reject the AMC hypothesis for purring, they do show that cat larynges can easily produce sounds in the purring range with fundamental frequencies of 25 to 30 Hz without neural input or muscular contraction,” says study co-author Gerald Weissengruber from the Institute of Morphology at Vetmeduni.
“This strongly suggests that the physical and physiological basis of cat purring involves the same MEAD-based mechanisms as other cat vocalisations, such as meowing, and most other vertebrate vocalisations. Cat purring, however, is potentially augmented by AMC. We also believe that both AMC and MEAD are frequency-entrained in vivo,” says Gerald Weissengruber, summarising a further key finding of the study.
The article “Domestic cat larynges can produce purring frequencies without neural input” by Christian T. Herbst, Tamara Prigge, Maxime Garcia, Vit Hampala, Riccardo Hofer, Gerald E. Weissengruber, Jan G. Svec and W. Tecumseh Fitch was published in Current Biology.