Why do I get travel sick?

10 July 2018

Question

Why do I get travel sick?

Answer

Chris Smith put this question to GP Laurence Kemp...

Laurence - So this is all to do with the way your brain processes information from different senses. So we have our vestibular system, this is little semicircular canals of fluid that are part of the inner ear. And they’re what the body uses to sense movement. So when the head moves around, the fluid within these canals moves around and then we can detect that as movement. Now the brain then matches that up with information that's coming through from the visual sense as well: from the eyes. And we experience motion sickness when the two of them don’t marry up together. For example, if you’re driving in a car and youre looking out the windscreen at the front you’ve got the visual information coming in. Your vestibular system is feeling the direction you're going in the movements you're making and you’re less likely to feel travel sick under those circumstances. But if you're in a plane maybe with a bit of turbulence and you're trying to watch a movie on the screen in front of you, or you’re trying to read a book. The visual information that's coming in is that everything is static, there's no movement, but your vestibular system is telling you that things are moving and the brain doesn't like that.

Chris - So let me get this straight. There's a disagreement between what the brain thinks the eyes are telling it and what the ears are telling it. So logically it throws up to solve the problem. Why? That doesn't doesn't seem logical at all!

Laurence - Yeah I was trying to work this out myself. Essentially we didn't evolve as a species to be going in aeroplanes or going in boats at high speed. There's a vomit centre in the middle of the brain believe it or not. And when these mismatches occur the vomit centre gets stimulated the activity builds up and then it does rather rule the day. So I’m not sure there’s an evolutionary advantage to being really sick.

Chris - maybe it's a deterrent to to not do what you were doing that made you feel at that in the first place: dont do it again!

Laurence - But the interesting thing is as you do it more and more times your body habituates.

Chris - It gives in!

Laurence -  Your senses adapt to it so you know actually when you’ve been at sea or on a cruise boat for a few days you get your sea legs and you stop feeling the motion sickness

Chris - Have you ever had thing actually where you get, Erasmus Darwin who was Charles Darwin's uncle I think, first described it and said, he called it “mal de debarquement” because people who had been on the mail coach, he described it as, you know the stagecoach that drove the length and breadth of the country carrying mail around. When you get off that after a long giddy journey you would still sense this sense of movement in the absence of any movement and then people realised it’s the same with ships planes that kind of thing.

Laurence - Absolutely, it’s because your inner ear and your body's habituated to the fact that you’re moving and then the movement stops and essentially you have to habituate the other way there, that is the changed environment. And what makes it more interesting is that you know actually that because its a brain thing those other areas of the brain that feed into it as well. So people that regularly experience travel sickness, and my brother’s a prime example of this, he’s been travel sick you know I’ve childhood memories of him throwing up on you know every every roundabout on our holidays. You go on a plane with him now and he starts vomiting even before you’ve taxied onto the runway, so it’s psychological…

Chris - Don't’ travel with him!

Laurence - No no I try to avoid it to be honest, or at least be a good distance apart.


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