Why motion sickness makes us nauseous

by Stephanie Chasteen on March 20, 2009

Do dervishes get dizzy?  (taken by Tomas Maltby)

Do dervishes get dizzy? (taken by Tomas Maltby)

If you spin around and around, why is it that you can feel a little sick? The answer lies in how we sense our balance, and an ancient disease of the gut. We get our sense of balance in large part from the vestibular system of the inner ear. A delicate little set of organs in there contain fluid, and having a good sense of balance requires that these “fluid spaces” be properly maintained. However, our balance is, of course, also determined by what we see (try standing on one leg with your eyes closed).

When you spin around, the fluid in your inner ear gets sloshed around, momentarily confusing that sense of balance. Your eyes tell you you’re standing still, but your inner ear tells you you’re still spinning. Your brain panics when it gets this disconnect between the messages from your inner ear and your eyes. That’s because this is one of the signs of botulism poisoning. Botulism affects the inner ear and can result in this kind of disorientation. So what does the body want to do? Vomit, to get out that nasty toxin.

You can get the same effect if your eyes tell you you’re moving (for instance, walk into a room where the walls appear to move) but your inner ear tells you you’re standing still.

{ 4 comments… read them below or add one }

David Samuels March 20, 2009 at 3:19 pm

Actually, there’s an article in this month’s Scientific American which says that this might not be the entire story – instead, there is increasing acceptance for a theory that says inability to control your posture well causes the sickness, which appears to be borne out by some evidence that simply widening your stance, from 5 cm to 30 cm, reduces motion sickness incidence from 60% to 20%.

Mrs. CH March 20, 2009 at 4:38 pm

Very cool! Perhaps something related – what happens when you’re drunk and the room starts to spin? Do we know what causes that? Is it something similar?

sciencegeekgirl March 20, 2009 at 4:38 pm

How interesting! Here’s a quote from the article:

Stoffregen instead argues that motion sickness comes from the brain’s persistent inability to modulate the body’s movements in a challenging environment. Postural instability the inability to maintain balance was considered a symptom of motion sickness. Not so, Stoffregen says. Although postural control relies on sensory feedback, motion sickness is really a sign that the motor-control system is going haywire.

So, our inability to keep our balance when we’re dizzy may actually *make* us nauseous (rather than being a result of motion sickness). So, perhaps my tongue-in-cheek question underneath the photo — of whether dervishes get dizzy — is actually right on. They don’t get dizzy because they’ve trained themselves to maintain good balance and control their posture.

I’m also reminded of my experience in contra dancing, which involves a lot of spinning and twirling. New dancers get dizzy. Experienced dancers know to look into each others eyes (so you don’t see the walls of the room whipping past). So then the question becomes — does not seeing the walls whipping past help you avoid dizziness because (a) you keep your balance (Stoffgren’s theory) or (b) you avoid the disconnection between your eyes and your body (the original theory)? Or perhaps both.

David Samuels March 20, 2009 at 9:38 pm

My suspicion is that Stoffgren would say that the trick of fixing your eyes helps you keep your balance, and you could probably imagine a test (high-accuracy video followed by analysis of your center of mass as you spin) that would show that you do less wobbling as you get to be a better and more experienced dancer.

I don’t know – I have no personal judgment as to which idea makes sense, although the evolutionary biology-based explanation, basically the botulism one you explained above, always appealed to me because I love evolutionary just-so stories…

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