What Causes Motion Sickness? Here’s how to reconcile the mismatch in what your senses are telling your brain

My first experience of motion sickness was as a college student, standing on the back of a marine research vessel watching interesting things dredged up from the seabed off the coast of California. It was a day trip, the weather was good and the sea was calm. I was oblivious to the gentle pitching and rolling of the boat, instead focusing on the mud and organisms on a table in front of me.

Then I slowly started to get warm and drool. I felt exhausted even though I was well rested. There were intense waves of nausea and I started vomiting. It was a long afternoon. Once back on shore it felt like I was still moving. I didn’t feel normal until the next day.

In hindsight, this was the perfect situation for a bout of motion sickness. I was focused on my immediate environment – the table covered in ocean monsters – which was visually stable. My eyes were unaware that we were in fact moving up, down and back and forth with the waves. But my inner ear relayed all these movements to my brain. Sensory signals from my body’s muscles and joints provided information that resembled a cross between the visual input from my eyes and the balance feedback from my inner ear’s motion detectors.

In short, my senses were in conflict. I was in an environment that conflicted with lifelong expectations of how sensory information usually combines to inform me about the world. My brain recognized that something was wrong and tried to save me from things it was designed to deal with – poisoning or other illness. To my brain, emptying my stomach contents and forcing me to rest and recover seemed like the perfect solution.

For me, this event preceded a lifetime of work studying the vestibular system, the structures and functions of the inner ear and brain that allow you to stay oriented and stable in space. In my labmy colleagues and I reproduce these types of complex movements and conflicting sensory inputs and study how the brain uses them during development, normal adult behavior and disease. Ultimately, we hope to produce treatments for people who are disabled by a loss or disruption of these senses.

Mismatch of a great system and unusual situation

Any moving environment can cause motion sickness. It is usually not due to disease or pathology. Instead, motion sickness is the result of an optimally functioning nervous system, based on what it has learned throughout your life.

When processing sensory information and generating motor commands, the brain constantly monitors and adjusts its inputs and outputs to efficiently perform life’s tasks. For example, to see clearly as you turn your head, your brain moves your eye opposite and equal to the movement of your head. It does this based on feedback from the sensors in your inner ear that focus on balance. Your brain constantly monitors this reflex behavior, constantly adjusting to make sure your eye and head movements are perfectly aligned.

The efficiency of this system is based on experience and results, and it works well. It helps you get better at coordinating your movements and maintaining your balance as you grow, and helps you recover from imbalance and disorientation due to injury, illness and aging later in life.

The flip side of this process is that the nervous system is not prepared for things with which it has no experience. It partially explains why astronauts experience transient nausea as they adjust to weightlessness, why sailors get seasick, and why watching a movie on your iPad in the back seat of a car or playing an immersive virtual reality video game can become unpleasant. Humans as a species did not evolve to do these things.

So someone who is motion sick exhibits truly proficient and optimized functioning in a uniquely challenging and sub-optimal environment.

Lifetime changes

Typically, babies and very young children do not experience motion sickness. Older children are highly susceptible to motion sickness as they learn typical relationships between the different senses.

As people age into adulthood, the susceptibility to motion sickness usually decreases again, presumably because they are able to contextualize their experiences. In older adults, changes such as loss of receptor cells in the ear and eye, fogging of the lens of the eye, or loss of functioning in peripheral nerves can increase or decrease motion sickness. Usually, however, the incidence of motion sickness in a healthy older adult continues to decline.

A simple example of this is that my balance is actually better than that of my grandniece, who is a toddler. Her balance system and inner ear muscles are brand new. Mine isn’t. In fact, due to normal aging, I have lost many of the receptors in my ear that sense movement. However, I have learned to skillfully utilize the complement of sensory and motor functions I have, and over the years I have continually adapted to an ever-changing new normal. She has just begun this learning process.

Techniques for dealing with motion sickness

If you experience motion sicknessthere are several strategies you can use to feel better.

The first is to resolve the conflicting sensory information that creates your situation. Look at an earth-stabilized reference – focus on the coast or the horizon if you’re on a boat, for example, or if you go to the front seat of the car and look out the window. In this way you coordinate the incoming visual and inner ear vestibular information.

The second strategy is to reduce the information that causes the conflict. There are different drugs that work by suppressing vestibular information in the inner ear, and others that change the way sensory information is processed centrally in your brain.

You can also try to prevent the output of this conflict. Essentially, you can sabotage the central nervous system’s attempts to get you out of your situation by short-circuiting the mechanisms that trigger the motor response of vomiting. Taking anti-nausea medications reduces nausea without necessarily resolving the sensory conflict that caused it.

You can eventually, through repeated experience, adapt to many new situations. When your brain learns a new normal, you can function with fewer unwanted symptoms in the challenging environment. For example, NASA is developing preconditioning countermeasures to transfer astronauts faster and with fewer symptoms of motion sickness from Earth’s gravity to the weightlessness of space.

Studies like this will expand the range of environments in which humans can function and allow us to explore and ultimately live in what are new and novel worlds for us.