Purring is one of many noises that cats make, and it is the most common feline sound. Cats also hiss, growl, chirp, chatter and meow to convey feelings and emotions. While most people associate purring with a cat's happiness, it is a sound that has many different meanings.
The Science of Purring
Although purring is emitted as a vocal sound, it is a process that begins in the cat's brain. A purr begins when the repetitive neural oscillator sends signals to the laryngeal muscles, which tells them to begin moving. The laryngeal muscles start twitching at a rate of about 25 to 150 vibrations per second, which separates the cat's vocal chords during inhalation and exhalation to make the sound of purr. Purring is mostly associated with domestic house cats, but wild cats and some cat relatives, including genets and mongooses, purr too. Other members of the cat family roar to express emotions, but cats cannot both roar and purr.
Purring and Emotions
While purring can convey a wide range of emotions, there are several ways to tell what kind of purr the cat is making. People can sometimes guess what emotion their cat is feeling based on the cat's body language and environmental surroundings. A cat that is purring while lying in the warm sun is most likely happy and relaxed. A cat that starts purring at the veterinarian's office, in contrast, is more likely to be feeling scared or frightened. If owners cannot tell their cat's emotional state from other clues, they can often figure out what the purring means based on its pitch or tone, say experts at WebMD. Purrs that are produced when the cat is happy will sound like a gentle rumble when he or she exhales. Cats that are hungry or want something, in contrast, will emit purrs that are combined with a crying sound. A cat's cry is usually likened to a baby's cry, and for good reason. Researchers at the University of Sussex studied cats' purrs when they were hungry and found they produced sounds in the frequency range of about 220 to 520 hertz. Babies' cries cover a similar range of about 300 to 600 hertz.
Health Benefits of Purring
In addition to expressing emotions, purring is believed to be a source of healing power for cats. Despite the energy it takes, cats often purr when they are in pain. Researchers have discovered vibrations produced at speed of 24 to 140 vibrations per minute can help stimulate bone growth, heal wounds and relieve pain. Cats' purrs when they are injured fall within that frequency range. Purring may have other health and healing benefits for cats including reducing swelling and inflammation, and repairing injured muscles or tendons. Researchers have also found purring provides health benefits for humans. A study performed by the University of Minnesota Stroke Center discovered cat owners were 40 percent less likely to suffer from heart attacks than people without cats. They believe purring, which relieves stress and tension in humans, was the main reason.