Motion Sickness

Motion sickness or kinetosis, also known as travel sickness, is a condition in which a disagreement between visually perceived movement and the vestibular system’s sense of movement.  Depending on the cause it can also be referred to as seasickness, car sickness, airsickness, or simulation sickness.

Sopite syndrome is a neurological disorder that relates to prolonged periods of motion.  Symptoms includes dizziness, fatigue, and nausea.  If the motion causing nausea is not resolved, the sufferer will frequently vomit.  Unlike ordinary sickness, vomiting in motion sickness tends not to relieve the nausea.

About 33% of people are susceptible to motion sickness even in mild circumstances ; the remaining 66% are susceptible in more severe conditions.  Individual and animals without a functional vestibular system are immune to motion sickness.

Cause

The most common hypothesis for the cause of motion sickness is that it functions as a defense mechanism against neurotixins.  

When feeling motion but not seeing it, the vestibular system in inner ear transmits to the brain that it senses motion, but the eyes tell the brain that everything is still. 

As a result of the discordance, the brain will come to the conclusion that one of them is hallucinating and further conclude that the hallucination is due to poison ingestion.  The area postrema in the brain responded by inducing vomiting, to clear the supposed toxin.

Types

Motion sickness can be divided into 3 categories :

1. Motion is felt but not seen

In these cases, motion is sensed by the vestibular system and hence the motion is felt, but no motion or little motion is detected by the visual system,  e.g. car sickness, air sickness, sea sickness, centrifuges, spinning.

Reading a book, a map or interior or the car, which are motionless, in a moving car/airplane/boat tends to easily motion sickness.  While visual system sees the motionless objects ( book, map or interior of car/airplane/boat ), vestibular system senses motion, especially vehicle goes around corners or over hills, which cause the discordance. 

The effect may be lessened by looking outside of the vehicle.

Yet, there is little that can be seen outside of a window of an airplane due to the small windows. 

Travelers on sea crafts too find it difficult to visually detect motion even if they look outside of the boat, as water does not offer fixed point with which to visually judge motion.

When one spins and stops suddenly, fluid in the vestibular system continues to rotate, causing a sense of continued spinning while one’s visual system no longer detects motion.

2. Motion is seen but not felt

Motion is detected by visual system, but no motion or little motion is sensed by the vestibular system.  It is also referred to as Visually Induced Motion Sickness ( VIMS ), eg. motion sickness due to films / virtual reality, simulation sickness, space sickness.

This type of sickness occurs when watching films on especially large screen or 3D, or even TV.  Films or home videos shot by handheld camcorder without image stabilization technology tend to contribute to motion sickness. 

Playing computer or video games too will cause motion sickness.

3. Motion sickness that are seen and felt but do not correspond

When moving in a vehicle for a long time on a badly maintained road at a very slow speed, the visual and vestibular systems fail to correspond which cause motion sickness.  Vibration of vehicle give sense of severe motion to the vestibular system, but due to the slow speed the visual system doesn’t sense proportional amount of motion.

Prevention & Treatment

Motion sickness can be cured or prevented by :

- Look out of the window of the moving vehicle and gaze toward the horizon in the direction of travel.  This helps to reorient the inner sense of balance by providing a visual reaffirmation of motion

- In the night, or in a craft without windows, it is helpful to simply close one’s eyes, or take a nap.  This resolves the input conflict between the visual and vestibular system.  Napping also helps prevent psychogenic effects ( the effect of sickness being magnified by thinking about it ).

- Chewing gum, snacking or just chewing in general seems to reduce adverse effects of the conflicts between visual and vestibular systems.

- Fresh, cool air also relieve motion sickness slightly.  As does avoiding foul odours.

- Get plenty of rest.   Weariness and exhaustion may induce motion sickness.

- Avoid acidic, spicy or oily food.   Avoid caffeinated beverages and soft drinks.

- Drink plenty of water.  Do not skip meals.  Don’t over eat.

- Medications such as Dramamine ( dimenhydrinate ), Stugeron ( cinnarizine ), and Bonine ( meclozine )