Sep 30 2013

Why Isn’t the Spinning Dancer Dizzy?

This is not a reference to the spinning dancer optical illusion, but rather to real dancers. Why don’t ballet dancers get dizzy when they spin around? Partly this is due to technique – a technique called spotting, in which dancer keep their head in one position for as long as possible then rotate it around quickly back to their fixed position. You have likely noticed this while watching ballet dancers.

But spotting does not entirely explain the ability of experienced dancers to tolerate spinning without becoming vertiginous. A new study finds that brain plasticity is also playing a role – the brains of experienced dancers adapt by reducing the signals that would cause dizziness.

To clarify, the term “dizzy” is a bit non-specific. People use it to mean vertigo (the sense of spinning or movement), but also light-headedness (feeling as if you might pass out), just being off balance, or even for any vague sensation in the head. What is being addressed in this study is vertigo, the feeling you get if you spin around.

Vertigo derives mainly from the vestibular system, the sensory organs of which are in the inner ear. There are canals filled with fluid (endolymph) that will move in response to gravity and acceleration – movement and head position. When you spin around and then stop the fluid continues to flow for a minute or so, creating vertigo.

Sensory input from the vestibular organs is routed through the brainstem and then primarily processed in the cerebellum, the part of the brain responsible for balance and coordination. Vestibular input is processed along with visual input and proprioception (sensation of where your body parts are in three-dimensional space) to create a seamless sensation of where your body is and how it’s moving.

When these sensory streams conflict, that also causes vertigo or motion sickness. That is why you can get motion sick on a moving vehicle. Your visual and vestibular input don’t match. These sensations are ultimately experienced by the cortex.

Chronic spontaneous vertigo is a common problem. Often we do not find a specific cause, in which case there is likely some problem with the processing of the various sensory streams leading to a feeling of vertigo.

This is where the new study might have a potential application. Researchers looked at ballet dancers and rowers of equal physical conditioning. They then looked at their brains in fMRI scanners, and also their reflex eye movements (nystagmus), in response to being spun around. They found that the cerebellar and cortical areas that light up when subjected to spinning were reduced in the ballet dancers compared to the rowers, and this effect was stronger with experience.

The researchers concluded that ballet dancers over years of training suppress input from the vestibular system and the response to that input, so they experience less vertigo when spinning.

This finding is not surprising. For patients who experience chronic vertigo, vestibular therapy is an established and effective treatment ( for both central and peripheral vertigo). It is probably more effective than any medication.

Vestibular therapy consists of exercises that are designed to provoke vertigo to a moderate extent that patients do over and over again to “desensitize” them to the provocation and experience of vertigo. This is essentially the same thing as the plasticity described in the current study.  Of course patient do have to stick with the therapy for months for the benefits to really accumulate. It’s not a quick fix.

This is all one more line of evidence that the brain is a changing organ. It adapts to use, but slowly. It seems that almost any aspect of brain function can be altered with training and use. There are limits, of course, and this effect may not be sufficient to completely compensate for brain disease or damage. There is also no magic shortcut to altering brain function – it takes time and dedication. But it is nice to know that we can alter the neurons in our brain with sufficient effort.

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