What causes motion sickness and how to prevent it Health

My first experience with motion sickness was as a college student, standing on the back of a marine research vessel watching interesting things being pulled 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, focusing instead on the mud and creatures on the table in front of me. (Also read: Is motion sickness bothering you? Here are five tips to feel better)

Any moving environment can trigger motion sickness.  It is not usually due to disease or pathology.  (Sutterstock)
Any moving environment can trigger motion sickness. It is not usually due to disease or pathology. (Sutterstock)

Then, gradually I started to feel warm and saliva. I felt tired even though I was well rested. There were intense waves of nausea, and I began to vomit. It was a very long afternoon.

Once back on shore, I felt like I was still walking. I didn’t feel normal until the next day.

In retrospect, it was perfect conditions for a bout of motion sickness. I focused on my immediate environment—a table covered with sea specimens—which was visually static.

My eyes didn’t know that we were actually moving up, down and sideways with the waves. But my inner ear was signaling all this movement to my mind.

Sensory signals from my body’s muscles and joints were providing information that was like a cross between visual input from my eyes and 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 about how sensory information normally combines to inform me about the world.

My brain recognized that something was wrong and tried to protect me from things designed to cause poisoning or other ailments.

In my mind, emptying my stomach contents and forcing me to rest and recover seemed like the best solution.

For me, this event preceded a lifetime of work studying the vestibular system, which is the inner ear and brain structures and functions that allow you to orientate and stay still in space.

In my lab, my colleagues and I reproduce these types of complex motions and conflicting sensory inputs and study how the brain uses them during development, in normal adult behavior and in disease.

Ultimately, we hope to produce treatments for people who are disabled by the loss or disruption of these senses.

A mismatch of a great system and an unusual situation

Any moving environment can trigger motion sickness. It is not usually due to disease or pathology. Rather, motion sickness is the result of your nervous system working better, based on what you’ve learned throughout your life.

While processing sensory information and generating motor commands, the brain constantly monitors and adjusts its inputs and outputs to efficiently perform life functions.

For example, to see clearly when you turn your head, your brain moves your eyes opposite and equal to the movement of your head. It does this based on feedback from sensors in your inner ear that focus on balance.

Your brain constantly monitors this reflex behavior, constantly adjusting to ensure that your eye and head movements are perfectly matched.

The efficiency of this system is based on experience and results, and it works well.

It helps you coordinate your movements and maintain your balance as you grow, and helps you recover from imbalances and imbalances caused by injury, illness and aging later in life.

The downside of this process is that the nervous system is unprepared for things it has no experience with.

It explains why astronauts experience momentary nausea when adapting to weightlessness, why sailors get seasick, and why watching a movie on your iPad or playing an immersive virtual reality video game in the backseat of a car can be unpleasant.

Humans are not evolved to do these things.

So anyone who is motion sick is really performing efficient and optimized work in a uniquely challenging and suboptimal environment.

Changes over the life span

In general, infants and very young children do not experience motion sickness. Older children are at higher risk of motion sickness as they learn specific relationships between different senses.

As people grow into adulthood, susceptibility to motion sickness usually decreases again, possibly because they are able to contextualize their experiences.

In the elderly, changes such as loss of receptor cells in the ears and eyes, fogging of the eye’s lens or dysfunction of the peripheral nerves, motion sickness can either increase or decrease. In general, however, the incidence of motion sickness decreases in healthy older adults.

A simple example of this is that my balance is actually better than my granddaughter’s, who is a toddler. His inner ear balance system and muscles are brand new. I don’t have In fact, through normal aging I have lost many of the receptors in my ears that sense motion.

However, I have learned to skillfully use the complement of sensory and motor functions I have, and over the years I have adjusted to the ever-changing new normal. She is just beginning this learning process.

Techniques for dealing with motion sickness

If you experience motion sickness, there are several strategies you can use to feel better.

The first is to resolve the conflicting sensory information that is creating your situation. See the Earth-fixed reference – focusing on the shore or horizon if you’re on a boat, for example, or moving into the front seat of a car and looking out the window.

This way, you align incoming visual and inner-ear vestibular information.

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

You can also try to block the output of this conflict. Essentially, you can sabotage the central nervous system’s efforts to rescue you from the condition by short-circuiting the mechanisms that produce the motor response to vomiting.

Taking anti-nausea medications relieves nausea without necessarily resolving the sensory conflict that induced it.

You can eventually, through repeated experience, adapt to many novel situations.

When your brain learns a new normal, it allows you to function in challenging environments with fewer unwanted symptoms.

For example, NASA is developing preconditioning measures to allow astronauts to transition from Earth’s gravity to the weightlessness of space faster and with fewer symptoms of motion sickness.

Such studies will expand the range of environments in which humans can operate and allow us to explore, and ultimately live in, novel and new worlds for us.

By James Phillips, Associate Professor of Head and Neck Surgery and Director of UW Medicine’s Vertigo and Balance Center, University of Washington

This story is published from the Wire Agency feed without modification to the text. Only the headline has been changed.

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