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 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
gets two 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 you're accelerating.

Wait, your ear?

Your ear 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 filled with fluid.

When you move, the fluid
shifts and tickles the hairs,

telling your brain if you're moving
horizontally or vertically.

All this tells your body
which direction you're moving in,

how much you've accelerated,
even at what angle.

In a car,

your vestibular system correctly
senses your movement,

but your eyes don't see it,
especially when glued to a book.

The opposite can happen.

You're at the movies, and the camera
makes a sweeping move.

This time, your eyes think you're moving

while your ear knows you're sitting still.

But why does this conflicting information
make us feel so terrible?

Scientists aren't sure,

but they think there's
an evolutionary explanation.

Fast moving vehicles and video recordings

have only existed
in the last couple of centuries,

a blink in evolutionary time.

For most of our history,
there wasn't that much

that could cause this sensory mix-up,

except for poisons.

And because poisons
are not the best thing for survival,

our bodies evolved a direct
but unpleasant way

to get rid of what we ate
that was causing the confusion.

It's a pretty reasonable theory,
but it leaves 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 is more about

the way some unfamiliar situations

make it harder to maintain
our natural body posture.

Studies show that being immersed in water
or just changing your stance

can greatly reduce the effects
of motion sickness.

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

We know the more common remedies
for car queasiness --

looking at the horizon,
over-the-counter pills, chewing gum,

but none are totally reliable

nor can they handle
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.

In addition to researching
the latest space-age technologies,

NASA also spends a lot of time

figuring out how to keep astronauts
from vomiting up their space rations.

Like understanding the mysteries of sleep
or curing the common cold,

motion sickness is 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.