When Your Eyes and Ears Disagree
Read a book in a moving car and your brain gets two different reports. Your eyes see a page that is not moving. Your inner ear, home of the vestibular system that senses balance and motion, feels every turn of the road. Motion sickness comes from this gap between the motion you feel and the motion you expect.
Symptoms commonly include nausea, cold sweat, headache, dizziness, tiredness and loss of appetite. Sometimes the tiredness lingers for hours or even days after the trip, a condition known as 'sopite syndrome'.
Nearly everyone will feel motion sickness at least once in their life. About one-third of people are highly prone to it, while most others only get sick under extreme conditions. Women tend to be affected more than men, and the risk drops with age. It is nothing new either: people have described it since at least the time of Homer, around the eighth century BC.
Boats, Planes and Spinning Rides
At sea, the trouble grows because water gives your eyes no fixed points for judging movement. Fog makes it worse. But the biggest cause of seasickness is a natural instinct: people who feel the boat rolling often escape below deck. There they cannot see the outside world, so eyes and inner ear disagree even more.
Getting used to a boat's motion is called 'gaining your sea legs'. The funny part comes later. Back on land, it can take a good share of the time you spent at sea to feel steady again.
Planes cause the same problem. A plane can bank and tilt sharply while passengers see only the still cabin, especially at night or when clouds block the view. Spinning is another trigger. If you twirl and stop suddenly, the fluid in your inner ear keeps turning, so you feel like you are still spinning while your eyes see a room standing still.
Sick Without Moving an Inch
You do not even need to move. In visually induced motion sickness, your eyes see motion while your body sits still. Giant IMAX screens are a classic cause, since they love scenes of flying over landscapes or riding roller coasters.
Shaky home videos filmed on phones do it too. The person filming rarely feels ill, because the motion they see matches the motion they feel. Viewers later get only the shaking, with no sense of movement. Zooming adds to the effect, since our eyes cannot zoom. A tripod or image stabilization helps.
Virtual reality can be even stronger, because the headset blocks every outside reference point. When a system lags, even a small head turn can set it off. A 1995 US Army report looked at 742 pilot sessions in 11 military flight simulators. About half of the pilots reported after-effects of some kind, and 28 said their symptoms lasted more than six hours.
Why Astronauts Feel It Too
In zero gravity, the inner ear loses the pull it relies on, so the eyes and the balance system stop telling the same story. The result is called space motion sickness. Strangely, it was almost unknown on the earliest spaceflights. Those spacecraft were so cramped that the crew could barely move, especially their heads.
Once spacecraft got bigger and crews could float around freely, the problem grew. Around 60% of Space Shuttle astronauts felt it on their first flight. The first known case is now thought to be Soviet cosmonaut Gherman Titov, who reported dizziness and nausea aboard Vostok 2 in August 1961. On Apollo 9, astronaut Rusty Schweickart had symptoms bad enough that the mission plan was changed.
Today, estimates say between 40 and 80 percent of people who reach weightless orbit get it. Even the amount of room given to each space traveler seems to play a part.
A Poison Alarm and How to Calm It
Why would mixed signals make you feel ill? The best-studied idea, sensory conflict theory, says the brain receives two states of motion that cannot both be true. Another idea goes further. A brain area called the area postrema triggers vomiting when it detects poison, and it also settles clashes between vision and balance. When eyes and ears disagree, the brain may decide it is hallucinating, blame a poison, and try to clear it out.
The good news is that simple fixes exist. Keep your head still, lie on your back, look at the horizon or be the driver. Music and calm breathing can help too. Slow habituation, getting used to motion bit by bit, works best, and the military uses it for pilots, though it must be repeated at least weekly.
Among medicines, scopolamine is the most effective and comes as a skin patch. Common nausea drugs such as ondansetron do not work for motion sickness.
