Motion sickness

Getting sick in a car, on a boat, or while playing a video game is not weakness or nerves. It is what happens when the motion the body detects does not match the motion it expected.

Three systems report on motion at the same time. Vision, which sees whether the scenery is rushing past. The vestibular system of the inner ear, which senses which way and how forcefully the head is moving. And the somatosensory system, the one in the body and the joints, which registers posture and support. When the three do not say the same thing, there is sensory conflict, and that is the most accepted explanation for motion sickness. Reading in the back seat is the textbook case: the eyes see a page that is still while the inner ear feels every curve.

Those signals come together in the vestibular nuclei, a group of neurons in the brainstem, the lower part of the brain. From there, the vomiting center and the autonomic reactions, the ones you do not control, are switched on. It is triggered by the slow sway of a boat or a road, and also by the simulated motion on a screen. And it does not hit everyone the same: some people get sick from almost nothing, and others almost never do.