I’m a person who loves to go skiing. Every Thursday, I wake up early to drive an hour and twenty minutes for a fun day on the slopes. Unfortunately, the road to the ski mountain is windy and bumpy…and consequently I spend nearly every Thursday morning stopped along the side of the road, car sick.
So what causes car-sickness, and how can I prevent it so I can enjoy my time skiing? Actually, there is no difference between the cause of car-sickness, sea-sickness, and air-sickness (from airplanes). All have the same symptoms of nausea/vomiting, headache, a general feeling of being unwell, paleness, and/or sweating. Motion is sensed by three different systems: the inner ear, which is responsible not only for hearing but also balance, the eyes, and the deep-tissue skin. The vestibular system plays a major role in balance and spatial orientation, which is located in the inner ear. For example, when we walk somewhere, all these systems are coordinated: the eyes see movement, the inner ear senses movement, and the body feels that it is walking.
The leading theory behind motion sickness is that it is a defense against neurotoxins. The part of the brain responsible for inducing vomiting when poisons are detected is called the area postrema. This part of the brain is also responsible for resolving conflicts between vision and balance. There are three types of motion sickness: when motion is felt but not seen, when motion is seen but not felt, and when both systems detect motion but they do not correspond. When these systems transmit conflicting information, the area postrema attempts to resolve the system through vomiting.
Let’s take sea-sickness as an example. Pretend you are on a boat with no windows. When the boat is moving, the inner ear senses motion, and transmits this information to the brain. The eyes, however, tells the brain that everything is still. The brain thus concludes that one system is hallucinating, and further concludes that this hallucination is due to ingesting poison. The brain responds by forcing the body to vomit, which would get rid of the (supposed) toxin.
So back to my car-sickness. My eyes mostly see the interior of the car, which is motionless, while the inner ear senses motion as the vehicle goes over those rotten bumps in the road or around curves. My eyes are telling my brain that I am not moving, but my ear is telling my brain that I am. This is why closing my eyes doesn’t help: my ears still sense movement. However, looking off into the distance can be helpful, because it allows my eyes to sense motion, which corresponds to my inner ear’s detection. This re-orients the inner sense of balance by providing visual information that transmits motion.
Fortunately, there are some treatments that can help with car-sickness. There are medications available that block signals from the vestibular system, which helps alleviate the conflicting information sent to the brain. Sitting in the front seat of a car can be helpful too, because the eyes then sense the movement of the car through the front windshield rather than the backs of the seats, which transmits signals to the brain that the body is stationary. Some people also use motion sickness bracelets, which claim to work by applying pressure to the “Nei-Kuan” acupressure point. There is no strong evidence behind these bands’ effectiveness, however.