The mystery of motion sickness - Rose Eveleth

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Although one third of the population suffers from motion sickness, scientists aren't exactly sure what causes it. Like the common cold, it's a seemingly simple problem that's still without a cure. And if you think it's bad on a long family car ride, imagine being a motion sick astronaut! Rose Eveleth explains what's happening in our bodies when we get the car sick blues.

Lesson by Rose Eveleth, animation by Tom Gran.

Can you read in the car?

If so, consider yourself pretty lucky.

For about one-third of the population,

looking at a book while moving along in a car

or a boat

or train

or plane

quickly makes them sick to their stomach.

But why do we get motion sickness in the first place?

Well, believe it or not,

scientists aren't exactly sure.

The most common theory has to do

with mismatched sensory signals.

When you travel in a car,

your body is getting two very different messages.

Your eyes are seeing the inside of a vehicle,

which doesn't seem to be moving.

Meanwhile, your ear is telling your brain

that you're accelerating

Wait, your ear?

Yeah, your ear actually

has another important function besides hearing.

In its innermost part lies a group of structures

known as the vestibular system,

which gives us our sense of balance and movement.

Inside there are three semicircular tubules

that can sense rotation,

one for each dimension of space.

And there are also two hair-lined sacks

that are filled with fluid.

So when you move,

the fluid shifts and tickles the hairs,

telling your brain

whether you are moving horizontally

or vertically.

With all these combined,

your body can sense

which direction you're moving in,

how much you've accelerated,

and even at what angle.

So, when you are in the car,

your vestibular system correctly senses your movement,

but your eyes don't see it,

especially if they are glued to a book.

The opposite can happen, too.

Say you are sitting in a movie theater

and the camera makes a broad, sweeping move.

This time it's your eyes

that think you're moving

while your ear knows that you're sitting still.

But why does this conflicting information

have to make us feel so terrible?

Scientists aren't sure about that either,

but they think that there's an evolutionary explanation.

As you know, fast moving vehicle and video recordings

have only existed in the last couple of centuries,

barely a blink in evolutionary time.

For most of our history,

there just wasn't that much

that could cause this kind of sensory mix-up

except for poisons.

And because poisons

are not the best thing for survival,

our bodies evolved a very direct

but not very pleasant way

to get rid of whatever we might have eaten

that was causing the confusion.

This theory seems pretty reasonable,

but it leaves a lot of things unexplained

like why women are more affected

by motion sickness than men,

or why passengers get more nauseous

than drivers.

Another theory suggests

that the cause may have more to do

with the way some unfamiliar situations

make it harder to maintain

our natural body posture.

Studies have shown

that being immersed in water

or just changing your stance

can greatly reduce the effects

of motion sickness.

But, again, we don't really know what's going on.

We all do know some of the more common remedies

for car queasiness --

looking at the horizon,

chewing gum,

taking over-the-counter pills --

but none of these are totally reliable

nor can they handle

really intense motion sickness

and sometimes the stakes

are far higher than just not being bored

during a long car ride.

At NASA, where astronauts are hurled into space

at 17,000 miles per hour,

motion sickness is a serious problem.

So, in addition to researching

the latest space-age technologies,

NASA also spends a lot of time

trying to figure out

how to keep astronauts from vomiting up

their carefully prepared space rations.

Much like understanding the mysteries of sleep

or curing the common cold,

motion sickness remains one of those

seemingly simple problems that,

despite amazing scientific progress,

we still know very little about.

Perhaps one day the exact cause

of motion sickness will be found,

and with it,

a completely effective way to prevent it,

but that day is still on the horizon.