I learned this today. Seasickness is caused because of a discrepancy between the vestibular system and the eyes.
Just inside your head, you have your inner ear which is used for sound detection and for balance. The balance part is what causes seasickness. There are two parts: the cochlea and the vestibular system. The cochlea is concerned with sound and converts sound pressure into electrochemical signals for the brain. The vestibular system is concerned with balance.
The vestibular system has three semicircular canals that are filled with fluid. When you move your head, the fluid in these canals moves. The fluid pushes on the cupula, which has hair cells. These hair cells convert the acceleration in the fluid into electrical signals. The canals point in different directions, so your brain can detect horizontal movements, vertical movements, and rotation. It is basically a gyroscope in your head.
Without the vestibular system, we would not be able to stand up or walk. It also allows us to have the vestibulo-ocular reflex, something that allows us to move our heads rapidly and focus at the same time.
Seasickness is caused because our vestibular system is doing what it is supposed to do, but our eyes are telling us something else. A boat moves a lot, and often erratically, on the waves. The person on the boat moves with the waves and the fluid in the vestibular system detects the motion. It sends signals to the brain telling it that there is a lot of motion. However, the person doing the observing is also moving with the waves and the rest of the boat, leading the eyes to tell the brain that everything is stable. On land, if you are moving around, the rest of the room won’t be, and your brain knows this, so it assumes that if the surface you are standing on is not moving, you should not be moving. On a boat, your ears are telling you that you are moving but your eyes are telling you that you aren’t.
When the brain receives these conflicting signals, it releases stress hormones, such as adrenocorticotropic hormone, cortisol, and antidiuretic hormone. These hormones can cause nausea.
Is there a cure for seasickness? There is, actually. But it is not a magic cure. It is time. If you spend long enough on a boat, your brain will adjust and become used to the new signals. Our bodies are incredibly good at adjusting to new situations. However, until your body adjusts, you can do a few things. Stay outside of your cabin and look at the horizon. If there is less to confuse your eyes, your seasickness will improve. You can also get medication that reduces the nausea.
So, seasickness is caused because your vestibular system is telling you that you are moving, but your eyes are telling you that you are staying still. Your brain reacts to the mixed signals by releasing stress hormones that cause nausea. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Motion_sickness
https://oceanservice.noaa.gov/facts/seasickness.html
https://www.michiganneurologyassociates.com/blog/what-are-inner-ears-and-how-do-they-affect-balance
https://en.wikipedia.org/wiki/Inner_ear
