Q: What causes seasickness? What can I do about it? – Call Me Ishmael
Dear Ishmael,
Motion sickness comes about when the brain encounters a mismatch between the visual impression of motion delivered by the optic system and motion sensed by the vestibular system of the inner ear (those tiny semicircular canals you’ve heard so much about).
Both the visual and auditory systems are set up to detect motion and help the brain keep the body oriented to its surroundings. Usually, these two systems work in tandem and that’s fine when we are moving about under our own power. But when we step into a moving object, a problem arises that the brain cannot easily reconcile. The inner ear says “hey, we are moving.” They eyes, on the other hand, can become fixed on the immediate surroundings – say, the inside of the car – and send the brain a contradictory message: “we’re standing perfectly still.”
The messages can just as easily be reversed: the eyes say we’re moving while the ears say we’re standing still. The Iron Shrink once got a hefty dose of that particular brand of motion sickness while playing the video game Doom. Never again.
Physiologists have a good idea of where in the brain the conflicting signals collide, but the reason for the ensuing nausea and other symptoms are a bit more mysterious. The psychologist Steven Pinker believes that the brain interprets the conflicting signals as a symptom of poisoning.
Pinker rightly points out that many toxins (such as one might ingest with spoiled food) act on the central nervous system. Wacky, contradictory messages of the sort that lead to motion sickness are interpreted as sign that something dangerous has been eaten. The brain responds by ordering the stomach to expel its contents before more poison can be absorbed into the system. That’s as good and logical an explanation as I have encountered.
Keep Your Eyes On the Horizon
The most efficient way to prevent motion sickness is to eliminate one of the contradictory signals being detected by the brain. For many people, simply closing their eyes works. But that’s not the best solution if you’re in the driver’s seat. The other option is to block the messages being sent by the inner ear. That’s where medications come in.
Being the seafaring sort, Ishmael, I’m sure that you’ve heard of dimenhydrinate, commonly sold under the brand name Dramamine. It’s an antihistamine that suppresses inner ear function and is sold specifically for prevention of motion sickness. Take it 30 to 60 minutes before travel, says the box, and make sure you check its many cautions and contraindications.
Unfortunately, like all antihistamines, dimenhydrinate has side effects that can include drowsiness. This, too, is a less-than-ideal solution for the Captain of the ship. Other drugs such as scopolamine and phencynonate hydrochloride (anticholinergic in nature, in case you care) have shown success in preventing motion sickness but they also feature prominent side effects.
If you don’t want to take medication there are other options. For instance, if you can’t close your eyes, then fixing your eyes on the horizon helps the brain reconcile contradictory movement messages (this is easiest when you’re sitting in the front seat of the car rather than in back).
Acupressure has shown mixed results in clinical trials. One study suggested that this natural remedy helps some people get some relief from motion sickness. Another study suggested that “acustimulation” bracelets that purport to prevent motion sickness are no better than a placebo (and a placebo is cheaper).
One of the more promising non-pharmaceutical approaches is autogenic feedback, in which students use biofeedback to learn how to regulate physiological responses to conflicting motion signals. For example, motion sickness includes constriction of surface blood vessels (hence the visible pallor associated with the condition). By learning to regulate that and other sympathetic nervous system responses some students are able to indirectly manage nausea and dizziness.
Habituation is another option that works for some. If you’re like me and you don’t have the time or money to invest in autogenic feedback training you might simply go to the amusement park and ride the Barf-O-Matic until you get used to it.
Finally, on behalf of the male gender, I would like to point out that women are more susceptible to motion sickness than men. What’s more, susceptibility to motion sickness varies throughout the menstrual cycle. This is iron-clad proof that men are vastly superior to women when it comes to hormonal interaction with visual-vestibular disparity. Take that, Gloria Steinem!
-IS
References:
Alkaissi, A., Ledin, T., Odkvisk, L. M., & Kalman, S. (2005). P6 acupressure increases tolerance to nauseogenic motion stimulation in women at high risk for PONV. Canadian Journal of Anesthesia, 52(7), 703-709.
Chuan-Gui, L., & Liu-Hong, Y. (2005). A new central anticholinergic anti-motion sickness drug phencynonate hydrochloride. Zhongguo Yaolixue Yu Dulixue Zazhi, 19(4), 311-320.
Cowings, P. S., Toscno, W. B., Timbers, A., Casey, C., & Hufnagel, J. (2005). Autogenic feedback training exercise: A treatment for airsickness in military pilots. International Journal of Aviation Psychology, 15(4), 395-412.
Flanagan, M. B., May, J. G., & Dobie, T. G. (2005). Sex differences in tolerance to visually-induced motion sickness. Aviation Space and Environmental Medicine, 76(7), 642-646.
Gil, A., Nachum, Z., Dachir, S., Chapman, S., Levy, A., Shupak, A., et al. (2005). Scopolamine patch to prevent seasickness: Clinical response vs. plasma concentration in sailors. Aviation Space and Environmental Medicine, 76(8), 766-770.
Holmes, S. R., King, S. J., Stott, R., & Clemes, S. (2002). Skin pallor increases during motion sickness. Journal of Psychophysiology, 16, 150-157.
Miller, K. E., & Muth, E. R. (2004). Efficacy of acupressure and acustimulation bands for the prevention of motion sickness. Aviation Space and Environmental Medicine, 75(3), 227-234.
Pinker, S. (1999). How the Mind Works. New York: W.W. Norton & Company, Inc.
Sang, F. Y. P., Billar, J., Gresty, M. A., & Golding, J. F. (2005). Effect of a novel motion desensitization training regime and controlled breathing on habituation to motion sickness. Perceptual and Motor Skills, 101(1), 244-256.