In another life and probably like many little girls (or at least, all the ones in my dance classes), I took 14 years of ballet lessons. They gave me grace and a pretty good sense of balance.
One of the things I also ended up able to do was the fouettee en tourne:
(I was not NEARLY as impressive as this dancer)
And it looks great, right? Nothing elicits cheers from an audience quite like a truly huge series of fouettees, they're kind of the cheat to make people cheer. And they SHOULD cheer, what that dancer is doing took hours and hours of practice.
But now, try it. Try spinning around (not on your toes, on two flat feet, no injuries people!). After about three turns...the world starts to spin. You get dizzy. Because most people do. I remember getting dizzy as a child, and looking at the older dancers, and wishing and wishing I could be like them. But after a while, I was spinning like a pro. And even now, when I dance (salsa or something, say), my partners tend to be very impressed with my ability to spin. You can put me on my toes, start spinning me around, and GO. Two turns? Nothing. 3,4,5,6? Not a problem!
(Sadly, not me. Source)
There are a few tricks that ballet dancers use to help them spin. The biggest one is "spotting", fixing your eyes at a spot on the wall (or wherever you're headed), and keeping them there, whipping your head around at the last possible second to make sure your eyes stay put as long as possible. If you look in the video above, you'll see her head is turning just a bit faster than the rest of her. She's spotting.
But spotting alone doesn't make her, or me, good spinners. As we danced, our brains changed.
Nigmatullina et al. "The Neuroanatomical Correlates of Training-Related Perceptuo-Reflex Uncoupling in Dancers" Cerebral Cortex, 2013.
Long training of basically any kind is going to change the brain. Because let's be honest, pretty much everything changes the brain. Long term training in music changes the brain, for example. So does eating breakfast (at least temporarily). While we could just snark off and say "well everything changes the brain", what's fascinating are the different ways the brain is changed.
And in ballet dancers, the brain is changed in a very specific way. Dancers get very good at spinning because certain aspects of their brains desensitize to the turns. Specifically, the vestibular system, the system that controls your sense of balance and vertigo (dizziness), is desensitized in dancers, allowing them to turn more without getting dizzy.
But how exactly is it desensitized? To figure this out, the authors got 29 dancers with 16 years of experience (average age 21, all female), and matched them to 20 controls (also female, average age 21). I was very pleased to see they matched them for physical activity, dancing is very athletic, and the dancers worked out up to 20 hours a week, they managed to get controls that were matched to the average of 7 hours a week.
The first thing they did was test their vestibular-ocular reflex. This is a function of the vestibulocochlear nerve, and is the reflex responsible for making your eyes fix on a point during head rotation. So, for example, fix your eyes on this:
Now, fixing your eyes on "SCIENCE", turn your head to the right. Keep your eyes on the science. :) Your eyes will move left. That's the vestibular-ocular reflex.
To test this out, the authors used a swiveling chair, that spins people around in various ways. They can measure your vetibular-ocular reflex by measuring how much your eyes move. During it you turn a wheel with your hand, and you are supposed to turn it with the amount of rotation you feel you are experiencing, which allows them to measure the perception of the vestibular-ocular reflex, as well as the reflex itself.
(Figure 1: the sciencey version of the worst carnival ride you've ever been on)
From this test, they get two measures, which you can see in the graph on the bottom. The first is a measure of how dizzy you feel (perceptual, the grey trace), the second is the eye movement (the bottom trace). They were able to show that dancers had a decrease in the vestibular-ocular reflex. They moved their eyes less as they whipped around (remember my description of spotting?). And they also felt the turning less than controls. More importantly, the dancers sense of turning, and the vestibular-ocular reflex, were UNCOUPLED. They were not related to each other. So even though their eyes were moving in the reflex, they didn't feel it!
But what does this mean for the brain? The authors put the dancers and the controls into an MRI to measure the the grey matter volume (representing neuronal cell bodies), in the cerebellum, an area highly associated with balance and the vestibular-ocular reflex. They were able to show that the grey matter in the vestibular area of the cerebellum was lower in dancers than it was in controls, which might help explain the uncoupling between the feeling of spinning and the vestibular-ocular reflex in the dancers.
Of course, this is a correlation. It's possible that training can reduce the cerebellar grey matter and produce this effect...but it's also possible that the people who go on to be successful dancers have smaller cerebellar volume in that area to begin with. To really find this out, you'd have to take a bunch of people who never danced, run the tests, give them intensive dance training (a few years maybe), and run them again. Of course, many professional ballerinas began dancing when they were VERY young (I began when I was 4), and so some of these changes could have occurred during development. You'd need to take two sets of kids, run the tests on the kids, put half in dance and the other half in maybe another sport that involves no spinning, like soccer, and follow them over time. A more difficult experiment, but potentially extremely interesting.
But this study is important for more than dancers! It could also be very helpful to those who experience a lot of dizziness due to vesitublar-ocular problems. It could be that accustoming the patients to spinning (maybe through dance class?), might help uncouple the reflex from their perception, and help them feel less vertigo. A leap from dance to sickness that could be...dizzying. :)