The brain receives sound as well as balance signals from the inner ear via the auditory nerve. In the outer portion of the inner ear, called the cochlea, sound is magnified, transformed into electrical impulses and transmitted to the brain. At the same time, the semicircular canals inside the inner ear, which consist of tiny hairs and fluid, detect movement and keep balance. Those signals are sent to the brain as well.
Motion sickness happens when your brain gets confused about your body’s movement, which affects the vestibular system that normally helps us to maintain balance. The confusion stems from those signals from your inner ear, which controls balance, transmitting one thing, while your eyes see or perceive something else. The conflicting signals that reach your brain cause physiological changes in your body. You can get motion sickness not only from actual motion, such as while riding in a car or roller coaster, but also from perceived or anticipated motion, such as while watching a movie or just thinking about a past experience of motion sickness.
There are several medications you can take once seasickness takes effect or in advance to prevent its occurrence; however there may be side effects that impair your motor skills. The drug scopolamine, for example, minimizes the effect of the ship’s turbulence by preventing the brain from receiving conflicting motion signals. Antihistamines, such as promethazine, decrease nausea but cause drowsiness and shouldn’t be taken with alcohol. Some people recommend wearing acupressure bracelets that apply pressure onto the palm side of your wrist to reduce nausea. Finally, one theory recommends regular exposure to sea travel to get used to the motion.