Most people look at a purring cat and see a contented creature, and most of the time purring appears to signal contentment, but that is not always the case.
Like the cat itself, purring is mysterious. This signature cat behavior has puzzled researchers for decades, and many scientists have attempted to discover exactly how and why cats purr. While scientists now believe they understand how cats purr, questions about why they purr and how purring evolved remain.
How Do Cats Purr?
Surprisingly, the purring mechanism has proved a contentious subject. Early investigators believed purring was the result of blood flow patterns, but more recent evidence, including one study by Sissom, Rice and Peters in the Journal of Zoology, demonstrates that purring is the result of the rhythmic movement of the laryngeal muscles, the muscles that control the vocal chords. The brain signals these muscles to twitch at a certain frequency. When the muscles twitch, the vocal cords rhythmically separate as the cat breathes in and out. This rhythmic separation produces a purr.
What Makes Cats Purr?
Researchers speculate that cats purr for a number of reasons. Most scientists agree that purring functions as a means of communication with humans and other cats and that it might act as a form of self soothing. One interesting theory suggests that purring may also have a healing function.
Experts speculate that cats communicate with humans and other cats by purring. Mother cats purr when nursing kittens (who knead, another adorable but sometimes puzzling cat behavior), and kittens begin purring by the time they are a few days old. The purrs of these young kittens may serve to let their mothers know they are alive and well. Adult cats also communicate satisfaction and contentment to their owners by purring when being stroked, when rubbing against their owners’ legs, when being talked to or even just when they are around their owners.
Domestic cats also use purring to beg for food. In a 2009 study published in Current Biology, investigators found that cats add a high-frequency meow to their low-pitched purrs when they want food. Humans perceive these solicitation purrs as more urgent and less pleasant than normal purrs, so they respond by feeding or providing attention to the purring cats.
In addition to purring when they are happy and hungry, domestic cats purr when they are frightened, sick, hurt and dying. For this reason, most experts believe that purring serves as a means for cats to comfort themselves. Because cats purr when in distress, it is important for veterinarians and owners not to make assumptions about a cat’s mood based solely on the fact that it is purring.
Researcher Elizabeth von Muggenthaler believes that purring may be a healing mechanism. Using recordings of purring cats, she measured the frequency of their purrs and found a range of 25 to 150 Hertz. This frequency range is the same as the therapeutic frequency range used by doctors for a number of purposes including the following:
- Healing fractures.
- Relieving pain.
- Reducing swelling.
- Easing muscle strain.
- Increasing flexibility.
- Easing breathing difficulties.
- Encouraging bone growth.
- Treating wounds.
She reasons that purring may have evolved to serve these functions in cats. After all, for a sit-and-wait predator, like the cat, having a mechanism of self healing would be a significant evolutionary advantage. In the wild, cats spend most of their time resting and sleeping to conserve their energy for the hunt. Purring during these periods of rest may keep them in peak condition by helping to prevent muscle atrophy, keeping their bones strong and speeding recovery from minor injuries.
For more information on purring in cats, see the following sites: