Last week I discussed motion sickness, pointing out that it often has nothing to do with any inner ear disorder. However, occasionally it is directly related to an inner ear disorder. I will try to explain.
The sensory conflict with seasickness is prolonged. Brief sensory conflicts may result in brief disorientation, but typically don’t produce nausea. A common brief sensory conflict occurs while one is driving. We have all experienced it. Imagine yourself sitting in the driver’s seat, stopped at a red light, hands on the wheel. A large truck pulls up next you and stops. You are not really paying attention to the truck, then all of a sudden the truck pulls forward a few feet. You grip the wheel and press on the brake until you realize that the truck (not you) is moving. In this scenario, you get the same visual feedback as if your car were rolling backwards. The brain very quickly checks with the vestibular system to make sure there is no sense of movement, then concludes that the movement was in your visual field (the truck), not in your car (you).
People with reduced vestibular function may find these situations more difficult due to the decrease in vestibular information available. Patients with cerebellar dysfunction or on sedating medication may respond more slowly to the vestibular information telling them that they are not moving. In this last situation, a vestibular disorder may make the problem greater, but it is not the cause of the sensory conflict. I describe these types of situations as “fleeting disorientation.” The entire episode lasts less than a second or so, and there is no nausea or lingering disorientation. You basically just “lose it” for a second, realize you “lost it,” freeze momentarily, then everything is fine. There is danger if these occur while you are driving or doing anything else potentially dangerous.
I mentioned at the beginning of this post that sometimes motion sickness ( I prefer the term motion “intolerance” in this particular situation) can be the direct result of an inner ear disorder. I will address this topic in two weeks. But before that, I want to lay a little foundation. So, to do that, next week
I will delve into the physiology of the balance system.