Monday, January 18, 2016

The Purr

It's time for a cat story. Just a little one. A little one about one of this mysterious species' most asked about mysteries: the purr.

Little gladdens the heart of a veterinarian like a healthy kitten check-up, especially if it is after a long series of messy, complex, sad, smelly or chaotic appointments (in other words - a normal day). You walk into the room, introduce yourself and then proceed to stroke a fluffy happy kitten while discussing various easy kitten care subjects with the happy owners. I imagine that when some of you picture the life of the small animal veterinarian you picture something like this. Well, it represents somewhere between 2 to 3% of what we do (see reference to sad, messy, complex etc. above), but it is a lovely 2 to 3%. After the stroking and chatting you begin to examine said kitten. This is also pleasant as it hasn't learned to hate you yet. Then you place the stethoscope on the kitten's chest and hear.... amplified purring. This may sound cute, but it is annoying as you really do want to hear the heart and lungs. There are a few different tricks to get them to stop,  but my favorite is to carry the kitten with the stethoscope still in place over to the sink and then turn on the tap (slowly and carefully, lest you freak the kitten out and the visit shifts into the messy, complex, chaotic column). This almost always surprises them enough to make them stop purring for a few seconds.

The owners typically chuckle about this and then sometimes ask, "So why do they purr?"
My answer: "We don't know."
I was tempted to end the post there, just for dramatic effect, but that would be irritatingly glib. And it is also disingenuous as although we don't know for sure, we do have some decent guesses now.

First of all, what actually is a purr? There used to be all kinds of wacky theories, but the answer ends up being the most obvious one: the purr comes from a vibration in the larynx (voice box) controlled by the rhythmic pulses of a neural oscillator in the brain. Ok, the "neural oscillator" part may not be that obvious, but you might have guessed at the voice box. Cats with laryngeal paralysis can't purr. Some of you may have a cat that doesn't seem to purr. This does not mean that they have laryngeal paralysis as that is quite rare, but rather the thinking is that some purr so quietly that you cannot hear it. These cats will still have a vibrating larynx, but you would have to know exactly where to feel, how to feel and, most importantly, when to feel in order to detect this. The number who truly never purr is likely really very small, like people who truly never smile.

Which brings me to the main question, the why. Is it like smiling? The answer that is emerging from the fray of competing theories is that purring does resemble smiling in that it is used for social bonding, especially between kittens and their mothers (and cats and their owners with can openers). Moreover, like smiling, it results in endorphins being released. This also explains why cats don't just purr when they're happy, but also when they are injured or in pain. The endorphins provide natural internal pain relief. (Does this means you should smile when someone punches you in the gut? Of course it does.) Even cooler, to my mind, is the well supported suggestion that the vibrations from the 25 - 50 Hz frequency range of a cats' purr actually encourage tissue healing. The time may not be far off when we are told to strap a cat to our knee when we tear our ACL. Obviously some practicalities would have to be worked out first.

So, is there any downside to purring? Potentially yes:

No comments:

Post a Comment