Some people get car sick when they try to read on the road, other people do it blissfully, but if you’re one of those folks who just can’t get through a page without feeling nauseous, there’s finally a good reason for it. Essentially, your brain thinks it’s being poisoned. Here’s why.
The Science of Us explains in greater detail, but here’s the highlights, from an interview with neuroscientist and author Dean Burnett on NPR. In short, it all starts with the Thalamus, one part of your brain responsible for interpreting sensory signals. When you’re moving normally, or even driving, your body and brain are getting the same signals—you’re in motion, you feel the rumbling or rocking of your movement, you may even feel the distance you’re covering. When you’re moving but reading on the other hand, things are different, and those signals don’t jive:
"So what’s happening there is the brain’s getting mixed messages. It’s getting signals from the muscles and the eyes saying we are still and signals from the balance sensors saying we’re in motion. Both of these cannot be correct. There’s a sensory mismatch there. And in evolutionary terms, the only thing that can cause a sensory mismatch like that is a neurotoxin or poison. So the brain thinks, essentially, it’s been being poisoned. When it’s been poisoned, the first thing it does is get rid of the poison, a.k.a. throwing up. And as a result — so, like, as soon as the brain gets confused by anything like that, it says, oh, I don’t know what to do, so just be sick, just in case. And as a result, we get motion sickness because the brain’s constantly worried about being poisoned."
For some people, this reaction is stronger than others. If you’re just riding in a car, you can look out the window and see the world passing by, which can calm that sickness response. For others, reading on a train is fine, because you can still look up periodically and realise you’re moving—but for others, as soon as you focus on a page and tune out the rest of the world (and other visual sensory information,) well, that’s when it all goes downhill.
Of course, understanding why it happens doesn’t explain why it happens to some people and not others, aside from, as Burnett explained in his interview, that it’s just a quirk of neurological development. Some people are more adapted to not be sensitive to that response, and others are more susceptible to it. In either event, at least you know why it happens if it happens to you.