We don’t even really know why the sensory conflict actually triggers vomiting it is thought that some neural pathways activate the brain's vomiting centre, believed to be located in the medulla, part of the brain at the top of the spinal cord. We are aware that it seems to be much more common in women than in men, and appears to be strongly hereditary, but that’s about it. This causes a subtle movement known as body sway people deal with it subconsciously all the time. Our body is never truly motionless – muscles are always active even when we stand still. In the early 1990s, a group of researchers developed a different explanation, the so-called ‘postural instability’ theory, which states that people experience nausea in situations where they have not yet learned ways to maintain a stable posture. A 1968 study found that deaf participants on a narrow, wooden boat in 40-foot swells off the shore of Nova Scotia did not succumb to the condition.
This offers an explanation for the observation that a functioning vestibular system is a prerequisite to get motion sickness. Basically, when you’re in a car or a plane, your inner ear signals that you're moving, but your eyes say that you're not – because your body is motionless in relation to its immediate environment, such as your seat, the floor, or the seat in front. In simple terms, the central nervous system receives conflicting messages from the body’s balance receptors: the inner ears (vestibular system), the eyes (visual system), and the muscles down the back all the way to your feet (proprioceptive system).
The most popular explanation for motion sickness, however, is that it arises from a visual-vestibular mismatch.
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