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Motion sickness

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Motion sickness is a physical condition caused by a mismatch between actual and expected motion. It occurs when the brain receives conflicting signals from different sensory systems. Most people will experience motion sickness at least once in their lives. However, susceptibility varies significantly across the human population. About one-third of people are considered highly susceptible to these sensations. Women may be more easily affected than men. Symptoms can range from nausea and vomiting to dizziness and headaches. Some people also experience cold sweats, tiredness, or increased salivation.

The primary mechanism behind this condition is a sensory conflict. The brain relies on the vestibular system to maintain balance and detect movement. This system is located in the inner ear and detects motion mechanically. At the same time, the visual system provides information through sight. When these two inputs do not correspond, the brain becomes confused. For example, if you read a book in a moving car, your eyes see a stationary object. However, your inner ear senses the turns and bumps of the vehicle. This contradiction between the eyes and the vestibular system triggers the sickness.

Scientists categorize motion sickness into three distinct types based on how motion is perceived. The first type is motion that is felt but not seen, known as terrestrial motion sickness. This includes carsickness, which often happens when passengers look at small screens or books. Airsickness is another terrestrial form caused by the tilting or banking of an airplane. Seasickness occurs on watercraft and is often triggered by regular rocking or rolling motions. The second type is motion that is seen but not felt, called visually induced motion sickness (VIMS). This can happen when watching large IMAX films or playing video games. The third type occurs when both systems detect motion, but the signals do not match.

History shows that humans have observed these symptoms for a very long time. Descriptions of motion sickness date back to the eighth century BC during the time of Homer. In the early 20th century, the Austro-Hungarian scientist Róbert Bárány conducted important research. He studied railroad passengers looking out of side windows at passing scenery. He observed that their eyes moved back and forth in a specific pattern. He named this phenomenon "railway nystagmus" or "optokinetic nystagmus." Bárány published these significant findings in the journal Laeger in November 1921.

Space travel introduced a unique and intense version of this condition. In zero gravity, the vestibular system's gravity-dependent operations are interrupted. This prevents the visual and vestibular systems from providing a unified sensory representation. Space motion sickness can be more intense because weightlessness is an unfamiliar state. The first recorded case was Soviet cosmonaut Gherman Titov in August 1961. He experienced dizziness and nausea while aboard the Vostok 2 spacecraft. Later, Apollo astronauts Frank Borman and Rusty Schweickart also faced severe symptoms. On the Apollo 9 mission, Rusty Schweickart's symptoms were so bad they required mission changes.

There are several ways to manage or treat the symptoms of motion sickness. Behavioral measures are often the first line of defense. These include keeping the head still and focusing your eyes on the horizon. Medical treatments involve different classes of drugs to target the body's response. Antimuscarinics, such as scopolamine, are one type of medication used. H1 antihistamines, such as dimenhydrinate, are another common option. Some doctors may also use amphetamines like dexamphetamine. However, side effects can sometimes limit how much these medications are used.

Modern technology is even being used to help solve the problem of motion sickness. Virtual reality (VR) can sometimes cause sickness due to system lagging or software crashes. However, researchers are finding ways to use VR as a therapeutic tool. By using a headset, they can simulate a stable artificial horizon for the user. This provides visual cues that align with the body's actual movement. This method helps the brain reestablish sensory integration between the eyes and the ears. Such systems have shown great promise in helping people reduce seasickness within minutes.

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