Why Does Motion Sickness Happen?
A Mismatch in Information to the Brain Causes This Problem
Sep 16, 2009
Many people are susceptible to motion sickness, women a little more so than men and children, as many parents will know, are particularly vulnerable. The mode of transport makes a difference: many who are not car sick suffer from seasickness – in very rough seas almost everybody on the ship will succumb.
Symptoms of Motion Sickness
These often start with a sensation of fullness in the stomach area then very quickly turning to nausea. Facial pallor and sweating usually follow. If the motion continues vomiting may occur. The symptoms subside shortly after the journey has finished, in most people anyway, in a few unlucky individuals it can persist for some hours.
How Motion Sickness Happens
The body has a complex system of information processing which keeps us upright and maintains posture. Central to this process is the vestibular apparatus of the inner ears which provides information to the brain on the body's movement in space.
This information is integrated with signals from the eyes, muscles and joints to give the brain a precise picture of what position the body is in, whether or not it is in motion and in which direction it is travelling.
When seated in a moving car, aeroplane or ship the vestibular apparatus detects the motion but the rest of the system – the eyes, muscles and joints are detecting no motion or limited motion. This mismatch causes confusion in the brain and sends signals to the vomiting centre in the brain stem. The more the mismatch the worse the symptoms so that, for example reading in a car is more likely to produce motion sickness than if the passenger is looking out of the window.
It's easy to see why noxious substances in the stomach and the blood should induce vomiting but that association with disturbance in the balance system (and also with extreme pain) is a mystery.
Evidence that information from the vestibular apparatus is central to the problem of motion sickness comes from the finding that people without a working vestibular system (perhaps damaged by trauma, infection or surgery) do not suffer from this condition.
Treatment of Motion Sickness
Treatment falls into two categories: non-drug help and medication. It's sensible to try non-drug methods first, especially with children but sometimes the problem is severe enough to warrant drug treatment.
Non-drug Help
Simple methods can often be of benefit.
- Not reading in the car.
- Fixing the gaze on objects out of the window or in front of the car.
- Sitting in front of the car or over the wing of the plane.
- Lying down with eyes closed if possible.
- Eating stem ginger sweets or taking ginger powder capsules.
- Acupuncture: point P6 on the inner wrist is normally used. Wrist bands are available which apply acupressure to this point.
Medication
These work by interfering with the nerve signals coming from the vestibular apparatus and elsewhere. Two of the most commonly used are hyoscine and antihistamines.
Hyoscine is more effective than other medications and is best given before the journey. Some antihistamines cause drowsiness, those which don't have this side-effect are thought to be less effective.
This article is for information only. If you have any health concerns you should consult your doctor.
Resources
Human Physiology: The Basis of Medicine by Pockock and Richards Pub OUP 1999
Motion Sickness in Children Drug Therapy Perspectives. 2001;17(1)
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