Why do some people get motion sickness and some do not?

04 October 2016

Question

Hello Chris, I am emailing you from across the pond a K a Atlantic Ocean. Why do some people get motion sickness and some do not? I am legally blind and have neuropathy ataxia and love motion. Planes, rollercoasters and sailing ships do not make me sick.

Answer

We put Jordan's question to Heidi Solberg Ã~kland...

Heidi - So when I'm sitting in a car, there are multiple different receptors in my body and different systems that are telling my brain about where my body is in space and what it's doing, how it's moving. So, I've got receptors in my bum saying I'm sitting still and I've got pressure from my skin saying I'm sitting still. And then, at the same time, my vestibular system inside of the inner ear where there are these canals with fluid in them that kind of slosh about and tell my brain where I am in space and help me to keep my balance. And then there's also my eyes telling me whether or not stuff is coming towards me and moving from me which will tell me about whether or not I'm moving.

In a car, you start to get mismatching signals from all these different systems. So the vestibular system is saying we're moving because the car is accelerating or decelerating and, at the same time, my eyes and the rest of my body is telling me that I'm sitting still. So this creates a sort of mismatch and the brain doesn't really know how to interpret it.

Chris - So logically the brain says ah, the right thing to do is throw up?

Caroline - Yes, so why do we get nauseous? This is something we don't actually know why. There is a theory that was posed in the 70s which was that maybe this was to do with - normally when we had this sort of mismatch going on this would be because we'd eaten some kind of a toxic food or something that meant that we need to throw it up and get rid of it - so this is the brain's best guess essentially about what's going on. And that's why maybe it's making us nauseous, although it's not been proven, it's just a theory that we have.

Chris - But, returning to Jordan's question - which is why do some people seem to succumb more than others? And, also, are older people more susceptible than younger people because I've noticed that I was immune to the worst that the fairground could throw at me when I was the age of my children but as I've got older I've become more susceptible?

Caroline - Really, okay, interesting. I've read the opposite that sometimes older people will get less susceptible to motion sickness.

Chris - Maybe they just don't go on the fairground so much - that's what it is.

Caroline - So, individual differences can come from maybe that people have different levels of sensitivity in their vestibular system, so some people will be maybe relying more on their vestibular system than others to keep their balance or to know where their body is in space. So if you're very sensitive then maybe you're also more prone to motion sickness. Also your brain needs to know that you're okay, so if you train yourself to tell your body that this is fine and we're not in any danger and we're not being poisoned then, over time, you get used to it and then that stops this nausea from happening.

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