Last month we took a little deviation from our planned route to talk about Sir Ernest Shackleton’s epic adventures in Antarctica. One thing that I found fascinating was how they had endured almost two years “rockin’ and rollin’” in 60–80 foot waves riding in little wooden boats and never got seasick. Motion sickness was well known throughout the ages and even mentioned in biblical times. Back then it was called “camel sickness” and was produced by gentle swaying as the animals walked through the desert, causing nausea in most riders. “Lawrence of Arabia” (T. E. Lawrence) wrote in his 1926 autobiography, The Seven Pillars of Wisdom, that he was often sick to the point of incapacitation during his long camel treks. Samuel Clemens, aka Mark Twain, once commented on getting seasick, “At first you’re so sick you’re afraid you’ll die, and then you’re so sick you’re afraid you won’t die.” Some people are fortunate that they rarely if ever feel motion sickness, but nobody is immune to it, and it can be elicited under the right conditions in everyone. It can be totally incapacitating and it’s especially dangerous if it strikes a pilot in the cockpit, since motion sickness impairs dexterity, perceptual accuracy, and cognitive skills.
It’s not as uncommon as you might think; there’s a reported incidence of airsickness in 10% to 46% of military aircrews. It’s more common in newer pilots, but even experienced pilots can be affected. NASA reports that “space motion sickness (SMS)” affects 60% to 80% of astronauts, some of whom have tens of thousands hours of flight time. The official name of motion sickness is “kinetosis,” but whether you want to call it by its biblical name or its modern one, it’s a pretty miserable feeling. Nausea and vomiting are typical but there are a lot of other symptoms, including cold sweats, pallor, salivation, headache, and even muscle pain. Another symptom is profound drowsiness and persistent fatigue, which can happen even after brief bouts of motion sickness. It’s known as sopite syndrome, and signs of fatigue can persist for hours, days, or, rarely, even longer. Other symptoms are boredom, apathy (lack of interest), failure of initiative, increased irritability, and even changes in personality. It’s pretty obvious from this list that even a few of these symptoms in the cockpit could cause a real safety risk.
This topic fits in nicely with the last few articles about how we can be tricked by our senses as we navigate the world around us. Just like visual illusions, motion sickness is a disconnection from what our senses are telling us and what’s going on in our immediate environment. Most explanations for motion sickness center on a kind of “sensory conflict“ theory that is the result of our brain getting simultaneous but conflicting orientational information. Your eyes are telling you one thing but your inner ear is telling you something quite different. Inside the cockpit or car, the inner ear detects changes in both up-and-down and side-to-side acceleration as your body bobs along. But (there’s that “but” again) since your real position is fixed in the cabin that moves with you, your eyes register a relatively stable scene. This perceptual incongruity between what your inner ears “tell” you and what your eyes “see” causes the brain to release an assault of stress-related hormones that causes nausea, vomiting, and dizziness (vertigo). Another factor bringing on the symptoms relates to conflicts between the anticipation of orientational information and actual orientational information presented to the sensory organs of our inner ears. For example, pilots and drivers rarely get sick while they are doing the flying or driving, but if they fly/drive the same profile while someone else is doing the flying/driving, it can produce motion sickness.
We need to take one last course deviation to describe how our inner ears work before putting the inner ear, eye, and brain pieces together to explain why we feel motion sickness. Our inner ears (known as the vestibular apparatus) function a little like a biological attitude indicator (AI) giving us roll, yaw, and pitch information on our orientation and position in space. Another important function of this system that mimics AI information is calibration of our rate of acceleration and deceleration. To do all of this the inner ear contains three little fluid-filled tubes (the semicircular canals) arranged in three perpendicular planes. Each tube is filled with fluid (endolymph) and lined with thousands of hairlike receptors (called cilia and there are some cool videos at this link) that move when our motion pushes the fluid in those little tubes around. The movement of these tiny hairs stimulates nerve endings at the base of each hair cell, sending an electrical impulse through the vestibular nerves to the brain. The vestibular system and brain also have a positioning capacity that works a little like another panel-mounted instrument, our GPS. The brain takes all that AI and GPS information coming in from our inner ears and combines it with information coming in from the nerves in our spine and limbs (called the afferent nervous system) to tell us our body position, direction, and acceleration in 3-D space.
The last piece of the motion sickness puzzle is dependent on another important function of our inner ears called proprioception. Proprioception, which has been called our “sixth sense,” is the neurological foundation of all our motion, muscle coordination, and movement. Proprioception is part of that attitude indicator function of our inner ears and provides the information our brain needs to tell us where our limbs are relative to the space we occupy. It’s how, for example, you can walk around without watching your legs since we don’t need our eyes to tell our brain where our feet are coming down. It’s also the mechanism we use to drive a car and fly an airplane without having to watch or even think about where our hands are. There’s a test your doc might use at your yearly physical exam to check this whole system for you called the Romberg Test. It’s easy and you can do it now as you read this. Close your eyes, stand up, and rest your hands at your sides (don’t cheat—keep your eyes closed), then with your index finger touch the tip of your nose. Assuming everything is intact, your inner AI and GPS keep you balanced and tell your brain where your nose and limbs are in space and then navigate your hands to the tip of your nose. All this happens without you actually “seeing” any of it. The proprioception system is very sensitive and can be broken down easily. You might recognize the maneuvers of the Romberg Test as the same ones in a “field sobriety test” used by police if they suspect a driver of being intoxicated, since even small amounts of alcohol cripple the whole balance and navigation capacity.
Another way to test proprioception is to toss a ball (at least something that’s not breakable like your wife’s favorite antique flower vase) into the air. Watch the ball as it reaches its apex; keep your chin up and your eyes fixed on the spot at the top of the path of whatever you tossed. Without cheating and looking down at your hands catch the ball. It’s your inner ears, brain, and afferent nerves working together to put your hands right where the ball is going to come down. Pretty cool stuff, and it’s the link between motion sickness and proprioception that’s the key to understanding why we feel all the symptoms. Studies on motion sickness show that the positional information from this whole interconnected system is incredibly accurate. Even the slightest mismatch of vestibular information from your inner ears with visual input from your eyes that see relatively fixed immediate surroundings sets your brain into a wild frenzy. The stress hormones released by this informational assault cause all the creepy symptoms of motion sickness. A typical example of this sensory conflict is fixing your eyes on a map or the pages of a book while bouncing along a winding road or in rough air, which commonly brings on motion sickness.
Next month we’ll talk about why your passenger might feel violently ill in mild turbulence and why Shackleton and his crew reported never getting seasick in some of the worst weather and roughest seas in the world. We’ll talk about what you can do if it strikes you up in the air, and describe useful preventative methods that really work and don’t conflict with FAA regulations on in-flight medications use. Until then, stay close to the rail of the ship and carry an extra paper bag in the air.