What REALLY causes motion sickness.

I have read numerous explanations of motion sickness, that explain how the inner ear is responsible for equilibrium, and how conflicts between visual cues and sensations inside the ear can cause motion sickness.

What I have never seen is an explanation of how a loss of equilibrium can cause nausea and other symptoms. What is the connection between our inner ear and our GI tract?

Any info or links would be appreciated.

Nausea is caused by the brain, not the stomach, which can be triggered by a variety of causes. I would speculate that inner ear problems could easily be misinterpreted by the brain as a possible reaction to a toxin so it triggers vomitting.

Here’s SDStaff Hawk on Why do people get carsick.

From Medical College of Wisconsin HealthLink:

But it sounds like you already knew that much.

This STATEMENT ON MOTION SICKNESS includes a seemingly detailed report on the phenomenon (including the interesting news that amphetamine is a useful treatment), but doesn’t address what I believe to be your question, which I perceive as "How is it that conflicting signals from the inner ear and the eye cause the symptoms they do?

manny’s post refers to SDSTAFF Hawk’s column that really does not take it any further, only confirming the relationship between nausea and vertigo.

Further web searches turned up manny of the same as above, but I’ve failed to find the answer (and now that you’ve asked it, I’m curious too).

So, why does vertigo make your tummy do back-flips? Why not an earache instead?

Perhaps Ned is on to something with the body reacting to confusing news by purging the system of possibly newly taken-in contaminants.

To rephrase Ned’s description of the system’s reaction: “We ain’t shippin’ anything until we know why the kaphlooie-meter’s in the red!” I would say, though, that while in this case nausea may be brain-driven, I think it can originate in the tummy (GI tract).