Motion sickness is a condition in which motion causes extreme nausea. The sufferer becomes pale and perspires. If the motion persists, he or she vomits. Many people affected by motion sickness also experience belching, headaches, apathy, and sleepiness.
Motion sickness occurs in response to the movements of ships, automobiles, buses, trains, aircraft, and spacecraft. It may be called seasickness, carsickness, trainsickness, or airsickness, depending on the source of the motion. More than half the astronauts and cosmonauts who have flown in large spacecraft have experienced a type of motion sickness called space adaptation syndrome. Aboard spacecraft, as aboard ships, motion sickness usually appears during the first day of travel. It generally disappears after a few days, as the traveler gets used to the motion.
Motion sickness typically results from the effects of unusual motion on a person’s vestibular system, the organs of balance in the inner ear (see Ear (The sense of balance) ). Motions that cause sickness exceed the limits that the vestibular system can accurately report to the brain. In such cases, the vestibular system reports false information about bodily motions that conflicts with information reported by vision and the other senses. For example, the vestibular system might report that the body is moving upward, while the person’s eyes report that the body is moving downward. People or animals that lack the vestibular system are immune to motion sickness.
Research has shown that the vestibular system, in addition to its role in balance, functions as part of the body’s mechanism for detecting poisons. When certain poisons are present in a person’s blood, the vestibular system malfunctions and reports false information. After receiving this false information, the brain causes vomiting, which empties the person’s stomach of the poison before more of it can be absorbed into the bloodstream. Research suggests that motion sickness occurs when the brain interprets the false information from the vestibular system as being the result of poisoning. The brain then triggers vomiting as the appropriate action.
To help avoid or reduce motion sickness, a person should keep head movements to a minimum–by holding the head against a headrest, for example–and look at the distant horizon straight ahead. These actions prevent conflict between the motion information reported by the eyes and the vestibular organs. In addition, certain drugs help prevent motion sickness if taken before traveling. Some professional pilots with recurrent motion sickness have used biofeedback training to learn to control such body functions as heart rate and skin temperature (see Biofeedback ). For reasons not yet understood, voluntary control of such functions during exposure to motion situations can help control the symptoms of motion sickness.
