Motion Sickness

I have a very weak constitution. It doesn't take much time on a moving vehicle of any type to make be barf, and I've hurled all over gorgeous coastal areas in tourist destinations around the world. There was that one time in Italy, snapping photos of the incredible shoreline caves (now dubbed barf grottos), that one time scuba diving in Belize (after I had made it to the surface, thankfully), and in lobby trashcans of various finally stationary destinations (the video is of me, my sister, and my fiancé inadvisedly spinning around while at an archeological site in Greece earlier this summer, where I was lucky enough to avoid any emesis). While I am particularly susceptible to motion sickness, almost everyone with inner ear function will experience it at some point given the right tilting, oscillating, and generally vestibularly-disturbing circumstances.

What is going on in our guts and brains when we're in a moving vehicle that makes us throw up? Why can't we just deal with motion better? As it negatively affects so many, this nauseating (did you know: the word nausea itself comes from the Greek word for boat!) inconvenience associated with technologically-assisted travel by sea, land, air, or IMAX screens has been the focus of intense and sometimes wacky research for more than 100 years. Although a great deal of mechanistic evidence for how motion sickness happens has been described, the theories of why it happens are still controversial and fascinating.

i-fc00e3003ba7c92e8be37150ece3f199-VestibularSystem-thumb-250x190-53840.gifExperiences with motion sickness have been described since at least the time of Hippocrates, and until the late 1800's, the causes of motion sickness were attributed to "blood and guts theories", the symptoms thought to be the result of decreased cerebral blood flow or disturbance of digestive flow caused by the shaking of the viscera. When Victorian physicians started realizing that people who didn't have inner ear function never got motion sickness, the theories of what causes motion sickness completely changed. Instead of focusing on the humours, physicians thought that motion sickness was caused by vestibular overstimulation--when our balance-sensing systems are overloaded by rolling motion, our body freaks out and starts barfing.

The vestibular system of the inner ear is fascinatingly complex, made out of a series of tubes full of fluid sloshing around inside your head, activating nerves that tell your brain where you are and where you're going as the fluid tips and turns. Connections between the vestibular system and our muscles and eyes help to keep us standing upright and to make sure that we can see stable images even as we move our heads. While the Victorian observations made it very clear that the vestibular system is involved in causing motion sickness, it eventually was realized that overstimulation alone wasn't enough to explain the phenomenon. Overstimulating your vestibular system while jumping or dancing will almost never cause motion sickness, and drivers or pilots rarely experience motion sickness even while their passengers are vomiting, so control of your own motion is somehow important too, affecting how the signals of motion are being interpreted by your brain. Moreover, as basically anyone who's seen Cloverfield can attest, it's possible to feel motion sickness without moving at all, simply watching simulations of motion in movies or video games is enough to make many people sick.

Motion sickness is now understood as not just something that happens when your inner ear is overwhelmed, but arises when your brain is confused about what your eyes are seeing and what your vestibular system is feeling. When your body is moving but you can't see or control why you're moving, or when you see motion that doesn't correspond to what your body is feeling at the movies, the mismatch of the neural signals activates the vomiting center of the brain. Many of these neural pathways and brain structures were identified through a series of horrific experiments on dogs in the 1940's and 1950's involving destroying different parts of the brain and seeing whether the mutilated dog would throw up after being spun around on a swing. In the 1980's and 90's slightly more humane experiments on human undergraduates standing and vomiting on wobbling platforms added more data on the simply anatomical picture from the dog studies, providing mathematical models of the neural pathways involved in motion sickness, details on the types of motion that make it better or worst (0.2 Hz is the optimal barf frequency), how strobe lights or keeping absolutely still while in a moving vehicle can make symptoms better (some people think that this is why antihistamines like dramamine can help with symptoms of motion sickness), how ginger can make you feel less nauseous, and even connections between migraine and motion sickness susceptibility.

These studies offer suggestions for dealing with motion sickness through engineering or pharmaceutical interventions, but none really address why we suffer from motion sickness. Is there a reason that our brains can't process these contradictory eye/ear signals? Does motion sickness somehow actually make us stronger, or at least better able to survive to the next generation; is there a positive evolutionary selection for feeling sick? The fact that many mammals, like those poor postwar experimental dogs, and even fish being transported on trucks experience motion sickness points to a kind of evolutionary stability that many scientists have seen as evidence that there has to be an evolutionary explanation for motion sickness. Starting in the 1970's and continuing today, several evolutionary theories seeking to explain why we suffer from motion sickness have been published and debated, offering several scenarios for how such neural pathways could be selected for.

What kind of selective pressure would be so strong as to keep tricking our brain into barfing in harmless situations? One interesting idea is the toxin theory--during the billions of years of animal evolution, the kinds of motion that cause motion sickness are pretty rare relative to other things that could cause mixed sensory signals getting to your brain, like, for example, hallucinogenic neurotoxins. When your eyes and your ears are saying different things, your brain doesn't realize that this is the result of external motion, but thinks that you're hallucinating and forces you to throw up to expel the offending toxin. If you actually are hallucinating, barfing seems like a great response, and a great way to keep on living to produce more offspring.

Contrasting hypotheses point out that this theory can't really explain the fact that babies and toddlers--who are at relatively high risk for ingesting and being killed by toxins--don't get motion sickness when being carried around. A much simpler and much more recently published theory is the negative reinforcement model, which posits that motion sickness, instead of being a protective mechanism against toxins, is like pain--an unpleasant response to something that is bad for us and causes us to avoid the triggering behavior in the future. According to this theory, motion sickness teaches us to avoid the out-of-control motion that could injure us or leave us more vulnerable to predation. Certainly, spinning around all the time can make you fall down and a much easier target for saber-toothed tigers. In my cushy tiger-free life, motion sickness has provided the negative reinforcement to avoid spinning amusement park rides and sailboats (although not quite enough to stop getting in cars or planes when the destination seems worth it).

These theories can perhaps help satisfy our feelings of being betrayed by our own bodies, and can point to other toxin-sensing or negative-reinforcement neural networks involved, perhaps expanding our how understanding, but I'm always a little skeptical of this type of evolutionary argument. Even though my fiancé comes from a seafaring family, I don't think my motion sickness susceptibility is going to necessarily hurt my chances of reproducing. Although soldiers and sailors do have much higher stakes for being incapacitated by motion sickness, motion sickness became a fixed trait in animals way before the existence of humvees or aircraft carriers. Does there really have to be a positive evolutionary selection for motion sickness in order for it to exist? What if motion sickness is a completely arbitrary consequence of how our brainstems evolved, as some evolutionary biologists are beginning to think is the case for courting displays and secondary sex characteristics (check out Carl Zimmer's awesome post about arbitrary sexual selection and evolution over at The Loom: "Darwin, Sex, and Dada")?

What if as our brain develops in early childhood and we become more coordinated, the pathways that turn out to activate motion sickness in the wrong contexts get laid down too? What if there's no negative selection against motion sickness, or no positive selection for the systems that could stop it? Imagine there is some very costly way for our brains to be able to deal with conflicting sensory input, to avoid motion sickness, but having evolved without boats and cars and airplanes we didn't have the selective pressure for such a mechanism to be worth the cost. Next time I'm feeling seasick, as I try desperately to look to the horizon, clutching my ginger pills, all of these contradictory just-so stories will swirl in my head (just like my vestibular fluid), making me if not comforted that there could be an evolutionary reason for my discomfort, at least distracted from the worst of the queasiness.

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The bit about hallucinagens would be rather more convincing if hallucinogens made you throw up; in general, they don't; nor do they affect your sense of balance. (Not sure about neurotoxic ones though.) And while alcohol will make the room spin and make you throw up, in my (admittedly limited) experience, these don't usually happen at the same time. Interesting post though, thanks!

Whenever I tell someone I get motion sickness, they look embarrassed for me. My grandparents told me they thought I'd "grow out of it", as if it's something childish. Knowing a bit about the physiology of it, I'm baffled by those attitudes. It's just a thing I have, not really that different from allergies or asthma or any other conditions that lots of people have, in my opinion. What's the big deal?

I remember, as a child (age unknown but let's pretend I was ten), speculating on how the human of the future might evolve and coming up with the answer that the human of the future would not get motion sickness.

I didn't think through the question of why humans without motion sickness would pass on more genes (I don't know if I understood evolution at that level), but at the time it seemed a logical next step that the rational "I know why I'm moving: I'm in a car" brain would become more able to overrule the "This makes no sense: I feel sick" brain.

The answer to your question isn't particularly difficult nor is it a mystery. Humans, without acute smell or hearing, rely on visual reference for positional information (including balance), a result of becoming bipedal, where position reference relies on two, rather than three or four points of limb position reference with vestibular feedback.

How long can you stand on one leg, with eyes closed, before losing your balance?

That's not just a test of balance, but also of sensory processing and processing functions. If you have neuronal damage from inefficient repair (for instance, if you are chronically stressed or have insufficient sleep for long periods of time), you may have difficulty holding for balance for more than a few seconds. Likewise, if you are sedentary, motor neural networks that interact with those involving balance and coordination, may become impaired over time, for two reasons: activity promotes CNS repair and fine development (within muscle groups) and fine muscles that aid in major skeletal group coordination will shrink, loose strength and deteriorate.

Sailors have long known that in rough seas, you find a point of reference (usually the horizon) at distance and keep your eyes fixed on it to fight off motion sickness. You'll notice athletes, platform divers, dancers and acrobats doing it as well. Think of the ballerina spinning - she rotates her head differently than her body, to visually fix on a reference point as long as she can as she completes each revolution to keep from becoming nauseated. She is also using her head/upper body mass for (wind-up) impetus, too.

When you become drunk, your ability to maintain steady eye contact with objects in your visual field is disturbed (muscle relaxation, and nystagmus - involuntary eye movement). When you lie down, constantly shifting visual reference makes you dizzy (actually there is more going on in ketone toxicity in the brain, but we'll leave that off). As you correctly point out, signal mismatching within the brain sensory processing centers can make you feel as though you are moving, when you lying still.

If you have an unusually hair-trigger tendency towards light-headedness and vertigo, there is probably more than just a natural tendency happening. It's more pronounced with age, that points to barosensing neural degradation in the rear of the hypothalamus. Vertigo tends to go along with anxiety and stress pathology, too.

Oddly enough, my motion sickness due to movement isn't terribly bad. I have trouble as a car passenger on mountain roads, on small planes, and on ocean-going boats, but am generally just fine on commercial airlines, trains, on the water where there are minimal waves, and as the automobile driver. At amusement parks, I can go on a some rides, as long as they aren't too spinny or twisty... however, I get horrible, horrible simulator sickness: in movies, watching TV (and I don't just mean the bad handheld camera ones), playing any video game that is in the first person, and of course on real simulators. It's ended up being far more disruptive to my life than expected, and it doesn't hurt that people treat you like a crazyperson if you insist you need to stop watching a TV program because it's making you ill. As #2 mentioned, a lot of people do not treat motion sickness as a legitimate medical issue, often opting to assuming that you're being dramatic or crazy.

I used to get serious bouts of non-motive vertigo. In other words the crap would start just all of a sudden.

Still happens occasionally but now I've learned to recognize the warning signs. About an hour or so before an attack I just get this feeling. And they aren't so bad as to spin the room anymore. Just feels like the left side is stuffed up for awhile, generally anywhere from a few minutes to an hour or so.

The frequency of attacks has diminished too.

Two questions:

Do you suffer from migraines or chronic headaches or from TMJ disorder?

Do you get dizzy when subjected to strobe effects? Could be from watching TV, from irritating ads on the internet, or from fast natural light level oscillation - the effect of driving through autumn afternoon light broken up by many trees as you quickly pass by.

I do get sporadic migraines but flashing lights only bother me when I already have a headache. What are you trying to diagnose me with?

Another thing I just thought of: back in late 2001 when I was at university studying a completely unrelated field but reading widely, I came up with a hypothesis that children (/people) who get carsick would have messy rooms (/homes).

Or to put it better, that insofar as tidying involves vestibular sensations from all that bending down and picking stuff up off the floor, any difficulty in modulating those sensations while concentrating on a goal-directed task would lead to avoidance of the tidying.

At the time I emailed this suggestion to a researcher in a relevant field (as part of a larger discussion), who responded with interest saying that the idea was plausible and consistent with anecdotal observations (my paraphrase).

What do you think? And how tidy is your house? :-)

Ha! I love this hypothesis! Whether or not it's true I don't know but I will definitely use it as an excuse for leaving my clothes on the floor :)

Not trying to diagnose you with anything. Not my place, my function, nor my intent.

I was interested in your tendency towards CNS oxidative damage/repair and inflammation response.

Perhaps you have vagus nerve hypersensitivity (neuropathy). Comment #10 gets at one of the symptoms/causes: syncope and othostatic hypotension. That was why I mentioned defective baroflex/sensing capacity.

Great post with real useful information. thanks.

@2 - My father still thinks motion sickness is entirely controllable with willpower. Of course, he doesn't suffer from it in any normal situation. I, on the other hand, have suffered nausea (and the relatively slow vibration thing ties in nicely to my experiences) on any form of transport except push-bikes, horses and sailing boats from leaving the hospital at three days old. Cue family rows every time we had to travel. One of the reasons I stopped driving is that nausea could distract me to a dangerous extent: if as a passenger I need to fix on the horizon or just shut my eyes, that's OK, but it's not so good for the driver.

For completeness sake, I suffer from migraines (from childhood), and am prone to vertigo when tired or ill.

By stripey_cat (not verified) on 01 Aug 2010 #permalink

I've *never* had motion sickness while moving (not even below deck on a boat for the majority of the day), but I can't watch someone else playing a first-person computer game for more than a couple of seconds without getting horribly dizzy. How do you explain that? My sister, however, has to stare at the horizon on car trips, but isn't bothered by computer games or movies in the slightest.

Fascinating post nonetheless.

By Katherine (not verified) on 01 Aug 2010 #permalink

Back in the 1970s Dr. Pat Cowings did some interesting studies of motion sickness at NASA Ames. Seems Astronauts often have a problem with motion sickness. Dr. Cowings' experiments involved teaching relaxation techniques through biofeedback and inducing motion sickness via a spinning chair while the subject was blindfolded. As one of her test subjects, I can attest that the techniques worked. I still use them today.

This was a thoughtful post about a very complicated subject. I will put in my 2 cents as a researcher in the vestibular area of study.

My recollection is that Kennedy identified some of the most important factors to your susceptibility to be:

--who your parents were (genetic predisposition)

--how long the challenging stimulus lasts.

--what type of stimulus it was (e.g., three particularly bad ones are 0.2 Hz vertical oscillation at large amplitude, Coriolis cross-coupling, off-vertical rotation).

--your state of adaptation to that stimulus.

To these I would add:

--your state of (anti-motion sickness) medication.

--your state of conditioning (not the same as adaptation -- negative experiences lead to sensitization).

Compared to these, many other factors which get a lot of discussion (eating crackers, taking ginger, wearing acu-pressure devices, women more susceptible than men, etc.) are pretty minor.

By Ben Lawson (not verified) on 06 Jun 2011 #permalink

strangely i am quite comfortable in trains.
But when it comes to cars and buses i can hold my self from vomiting for no longer than 45 minutes to an hour.
One thing is even more strange that at night even in Bus or Cars i am comfortable enough i.e. i dont vomit.
I am almost forty now and this problem has been attached to my life.

By harshit jain (not verified) on 02 Jul 2011 #permalink

I had carsickness as a kid when traveling in the backseat. I was okay in the front though. Just recently I have been getting it while driving! It's awful I'm vomitting if I'm driving for just half an hour. I notice it's worse at night although it can happen during the day too. I thought it was my eyes and it helps a little now that I got glasses, even though they are a very weak prescription, but I don't think the prescription is exactly right. Gotta get them checked again because I still get sick. That was the first thing I thought of was my vision-that or a brain tumor! Have you had your eyes tested? Oh and I get migraines from the sun making that blinking through the trees and I end up sick with that. That make sense to me with the vision again. It's getting worse and worse . I'm getting one of those wrist bands to see if that helps too.

By givnmegryhr (not verified) on 22 Dec 2011 #permalink