The Reason We Get Carsick Is Unexpectedly Odd

Our brains think they’re under attack.

I’m not going to sugar coat it: Getting motion sickness sucks. I mean, how unfair is it that, during a road trip, some people can dig into a good book while many of us can’t so much as check our Twitter feeds without feeling sick? Well, turns out the reason we get carsick is because our brains are idiots that are constantly worried about being poisoned. Dean Burnett, neuroscientist and author of “Idiot Brain: What Your Head Is Really Up To,” recently appeared on NRP’s Fresh Air and spoke with host Terry Gross about all things neuroscience. During the interview, Burnett explained how our brains cause motion sickness. “One theory is…that it’s caused by a sensory confusion in the brain,” Burnett said, “and that when you’re walking — you know, like us humans tend to do a lot — there’s a lot of distinct signals being relayed to the brain…like the thalamus, where all the sensory information is put together and sort of, you know, fed to the other parts of the brain. So when you’re walking, you’ve got this, oh, the left, right, up, down sort of sensation.” Our brains are used to the natural sensation of walking, but moving vehicles are relatively new when compared to the amount of time it took for the human brain to evolve, and we apparently haven’t fully adjusted. According to Burnett, our muscular systems, the “tiny little tubes full of fluid” in our ears, and our eyes all work together to keep our brains informed of how our bodies are moving. But the brain gets confused in situations when your balance sensors are sending signals that you’re in motion—like when you’re riding in a car or train—while your eyes and muscles are saying that you’re not. Burnett says:

“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 poisoned. When it’s been poisoned, the first thing it does is get rid of the poison, aka throwing up.”

Burnett confirms the phenomenon that so many of us experience: Carsickness can be even worse when you’re reading a book. Since motion sickness stems from the brain being confused about movement, staring at a static page or screen can increase the “sensory mismatch” that causes the sickness. Here’s Burnett again:

“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.”

Burnett also explained that children tend to be more prone to carsickness because their brains are still developing, and are still in need of “being refined.” Um, what about those of us who never outgrew it? Thank god for Dramamine, I guess.

So, does Burnett agree that carsickness totally sucks? “It’s…inconvenient to say the least,” he told Gross. You can check out Gross’ full interview with Burnett at NPR.org.