Monday, August 22, 2016

What causes travel sickness? A glitch in the brain

Although one third of the population suffers from motion sickness, scientists aren't exactly sure what causes it.
Like the common cold, it's a seemingly simple problem that's still without a cure.
And if you think it's bad on a long family car ride, imagine being a motion sick astronaut!
Rose Eveleth explains what's happening in our bodies when we get the sea sick blues.

From The Guardian by Dean Burnett

With everyone holidaying for summer, travel sickness is going to be an issue for many.
But why? It could be an evolution-based glitch in the brain

lot of people, when they travel by car, ship, plane or whatever, end up feeling sick.
They’re fine before they get into the vehicle, they’re typically fine when they get out.
But whilst in transit, they feel sick.
Particularly, it seems, in self-driving cars.
One theory is that it’s due to a weird glitch that means your brain gets confused and thinks it’s being poisoned.
This may seem surprising; not even the shoddiest low-budget airline would get away with pumping toxins into the passengers (airline food doesn’t count, and that joke is out of date).
So where does the brain get this idea that it’s being poisoned?
Despite being a very “mobile” species, humans have evolved for certain types of movement.
Specifically, walking, or running.
Walking has a specific set of neurological processes tied into it, so we’ve had millions of years to adapt to it.

Think of all the things going on in your body when you’re walking, and how the brain would pick up on these.
There’s the steady thud-thud-thud and pressure on your feet and lower legs.
There’s all the signals from your muscles and the movement of your body, meaning the motor cortex (which controls conscious movement of muscles) and proprioception (the sense of the arrangement of your body in space, hence you can know, for example, where your arm is behind your back without looking at it directly) are all supplying particular signals.

There’s also the vestibular system, which includes the balance sensors; tiny fluid-filled tubes in our ears.
The fluid responds to the laws of physics, so moves about in response to acceleration and gravity, so we can tell when we’re upside down, for example.
And, of course, there’s our vision.
When we walk, the world travels past on our retinas at a steady rate, and there’s the gentle side-to-side rocking caused by our hips and legs etc.

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When we’re walking, all of this sensory information is fed into the fundamental, subconscious areas of the brain, like the thalamus, that integrate it into one coherent and rich perception of ourselves and the world around us.
However, vehicles haven’t been around long enough for our brains, at such fundamental levels, to “recognise” when we’re travelling in one.
Because when you’re travelling, all the usual signals of movement are absent.
Your muscles are still.
You’re sat down.
Being inside the enclosed space of the vehicle even restricts your view of the outside world, so your eyes don’t see much passing by.
This all results in sensory information that says to the fundamental brains regions “we are stationary”.
Not the vestibular system though; the fluid in your ears obeys physics, travelling at high speeds means it sloshes around even more than usual, so it’s telling the brain “we are really moving”.
That means these fundamental regions are getting mixed signals; usually reliable senses are now disagreeing.
What the hell can cause that? As far as the lower brain is concerned, only one thing; neurotoxin, aka poison.
And what’s the quickest way to get rid of poison? Throw up.
And so, we feel nauseous, and often vomit.

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You can see why this might be more common in self-driving cars; there’s a lot of physical movement and watching the road when driving, so the signals aren’t so mixed.
Take that and its associated movements away, and it wouldn’t be surprising to see increased motion sickness.
Some of you will know I cover all this in my book The Idiot Brain, so why rehash it here.
Well, the US version of the book was released three weeks ago.
I did some publicity for it, one item of which was an appearance on NPR’s Fresh Air, hosted by Terry Gross.

In this interview, I was asked about the part of the book that looks at travel sickness.
An interesting little hook to bring up in the mainstream, perhaps.
The New York magazine certainly thought so, dedicating a whole article to my offhand mention.
It has since snowballed from there, spreading from platform to platform to platform to platform to platform to (scientifically questionable) platform, finally arriving back here in the UK, where it started.

Now it’s appeared in the Mail, the Sun and the Telegraph.
This puts us in the slightly weird scenario where the Guardian was likely to be the only UK paper that hasn’t mentioned it, despite the fact that the originator of the story is already working for them!
 So I felt I’d best address it here.

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Another reason to cover it is that, as with most things that spread like this, inaccuracies, distortions and misinterpretations gradually seep in.
Now I’m reading stories that mention me by name that include claims and assertions that I’ve never heard before.
So, I’d like to clarify a few points.
I did not discover this mechanism, I just read about it.

It is not a new discovery.
I read about it years ago and didn’t realize until recently it wasn’t common knowledge.
It even has a Wikipedia page.

This is not definitely the mechanism why which motion sickness occurs.
There are other theories.
It may be a combination of all these things, or something else.
The one described above is the most persistent theory though.
And finally, anyone who has classed me an “expert” on something should be approached with caution.

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