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Getting lost in a good book while curled up in the passenger seat of a moving vehicle sounds like a good idea, but for many of us, reading in the car inspires nausea, or, in the worst-case scenario, even vomit.

But what causes car sickness?

In an interview with NPR’s Fresh Air, neuroscientist and author of the new book Idiot Brain, Dean Burnett posed the question, “When you think about it, moving shouldn’t make us sick. We move around all the time. We’re a very mobile species. So why—you know, why would moving suddenly make us want to throw up?”

The body is designed to move, he explained. When you’re walking, your body sends your brain all kinds of signals—from your eyes and your muscular system, and the “balance sensors” in your ears.

But when you’re traveling, your brain doesn’t quite know how to handle the conflict of sitting still while also moving at a great speed.

“When we’re in a vehicle like a car or a train or a ship especially, you’re not actually physically moving. Your body is still … Your muscles are saying we are stationary. And also your eyes,” he said. “But the fluids in your ears, they obey the laws of physics. And they are sort of rocking and around and sloshing because you are actually moving. So what’s happening there is the brain’s getting mixed messages.”

“There’s a sensory mismatch there,” he continues. “And in evolutionary terms, the only thing that can cause a sensory mismatch like that is a neurotoxin or poison. “

And what happens when your brain thinks you’ve been poisoned?

“The first thing it does is get rid of the poison,” Burnett explained, “aka throwing up.”

Lovely. And reading while riding only compounds the issue, according to Burnett.

“When you’re in a car, you can look out the window. You can see things going by. You can see the passage and movement itself, so that sort of balances the system,” he said. “But when you’re reading, you’re looking at sort of a small, static square. And, you know, the external information which would say you’re moving, that’s shut out even more than it would otherwise be … So it sort of increases the sensory mismatch, which is causing the sickness in the first place.”

So, if you’re road-tripping this summer, consider saving your beach read for the lounge chair. Your stomach will thank you for it.

From: Town and Country