HOW COME? Motion sickness is all in the mind

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I can't read on a car or bus without feeling dizzy. However, I can read without problems on a train. How come? asks reader Ken Riebold.Nausea, dizziness, headache, vomiting: Besides riding in cars, we may even feel woozy while we play video games, or stare down at moving graphics on a smartphone or tablet.

Our perception of movement is at the heart of motion sickness. But while we may be fine when we're controlling our own movements -- say, running along a twisting path -- step onto a boat, and all bets are off.

Our brains are responsible for figuring out just where we are in local space. The brain gets signals from skin pressure, joint position, eyes and ears. Our ears are especially important, because they contain built-in motion sensors: Fluid-filled semicircular canals detect angular motion (whirling on a merry-go-round). And calcium crystals (otoliths) move in response to gravity and straight-line acceleration, providing the brain with more information.

But in a moving enclosed space, position signals can be in conflict. Take, for example, the backseat of the car, where many people experience motion sickness. Your eyes may be focused on the seat in front of you, which appears to be standing still. Meanwhile, each time the car slows or speeds up, or travels around a curve, your ears tell your brain you're moving.

Result? A mismatch between the information being processed by the brain and its stored "library" of motions. Although no one is sure why, the sensory discrepancy can lead us to feel nauseated and dizzy.

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Many people report less motion sickness on smooth-riding trains than in swaying buses, traveling in fits and starts. A 2011 study found that trains made to tilt produced more motion sickness. But train sickness could be reduced by adjusting the tilts' timing -- tilting quickly at the beginning and end of a curve, versus a stomach-churning slow tilt over the curve's length.

Meanwhile, University of Minnesota researchers have found that while we all sway a bit as we move, the more wobbly we naturally are, the more motion sickness we're prone to have. And a team at Montreal's McGill University have discovered a motion detection center in the brain's cerebellum. This small cluster of neurons reacts in a fraction of a second to adjust our body's movements. These neurons seem to process "sensory conflicts," and scientists hope that further study will unravel more of the mysteries of motion sickness.

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