Motion sickness: A new theory

Jul 15, 2017

Motion sickness is a phenomenon that can keep many people from enjoying a cruise, an amusement park ride, or even a drive in a car. And with the advent of virtual reality, you don’t even have to be moving anymore to experience motion sickness.

New studies are challenging the assumption that motion sickness has to do with the relationship between the inner ear and the vestibular system, which provides sensory information about motion, equilibrium and spatial orientation. “Take Care’s” guest this week is Dr. Thomas Stoffregen. He’s professor of kinesiology at the University of Minnesota and has been studying motion sickness for more than 25 years.

The original theory, based on the motion sick person being in an unusual situation, assumes that the stimulation of your eyes, middle ear and other sensors in your body are different than normal experience because you’re on a boat or in a car. That different experience is what makes you sick, Stoffregen says. And he says he does believe in this difference.

“In those situations the stimulation of those sensory systems is different. There’s no question about that,” Stoffregen says. “The issue -- the debate, if you will -- is whether that difference is what actually is responsible for motion sickness and my argument is that it is not.”

What’s different when you’re on a boat?

Imagine you’re on a ship. Unlike standing on the ground, what you’re standing on is moving underneath you, hopefully on the way to a tropical destination. Stimulation of the sensors in your body, like your ankles, is going to be very different. Those sensors will pick up unusual patterns from your eyes down to your feet.

“But that is not the only thing that is different about being on a ship,” Stoffregen says.

When something is moving underneath you in an uncontrollable way, the physical control you have over your body will be challenged.

“There’s a sort of physical learning, motor-skill learning component there. Some people pick up motor skills really rapidly,” says Stoffregen. “Other people don’t learn quite so rapidly.”

This theory is called postural instability.

Why cars are like boats

Interstate highways and cruise control can be a motion sickness sufferer’s best friend. Why? Because the motion is consistent and nearly unnoticeable.

People get car sick, reading, for example, when they’re stuck in traffic.

“What that means is that when they’re slowing down and speeding up, turning left and turning right, that all means accelerations of one kind or another,” Stoffregen says. “Accelerations are an issue because they displace the car underneath you and now we’re right back where the ship was.”

The horizon line is your friend

A ship or a car is moving relative to the Earth. The horizon is, essentially, the edge of the Earth. Normally, it’s not possible to distinguish the motion of the ship from the motion of the body -- until you have a set point (or a marker) for which to measure that otherwise unpredictable motion.

“If you can gain information, obtain information about the horizon, then in principle that gives you information about how the ship is moving relative to the Earth, which in turn makes it possible, again in principle, for you to say ‘Oh, this much of the motion I’m feeling is coming from the ship and the rest of it, therefor, is coming from me,’” Stoffregen says.

Finding the horizon line could help the chronically motion sick.