The technique presumably works because it helps control gravity sensors in the abdomen--a lesser-known input to our fine-tuned balance system.

The brain is traditionally thought to sense body position in three ways. The inner ears sense motions of the head; the eyes see where the head is; and tiny sensory organs in muscles and tendons sense where the rest of the body is.

Recently, researchers have realized that sensors in many other parts of the body also play a role: in the abdomen, the lower organs, and even blood vessels. As long as all of these sensors send matching signals to the brain, we feel oriented. But if one or two don't match up, the brain gets confused and we become nauseated.

Gut feeling

Scientists knew the most sickening motions closely match the rate of natural breathing; they also knew that people naturally tend to breathe in time with the motion. In fact, Navy seamen in World War II discovered that they could use certain breathing tricks to combat motion sickness. But no one had ever tested whether breathing out of time with a motion could prevent nausea.

So why do these tactics work? Abdominal sensors are known to send motion signals to the brain more slowly than those in the inner ear because they're farther away from the brain and because abdominal organs have more mass, which means they resist movement a tiny bit longer. The time lag between the two types of sensors creates a mismatch that builds up in the brain and makes us gradually sicker, the researchers say.

But if the diaphragm opposes gravity-induced stomach motions with controlled breaths, there is less sensory conflict and less nausea.

"This technique is very good for mild everyday challenges," says medical research scientist Michael Gresty, a member of the study team. "It's completely safe, and it's not a drug."

The results appear in the December issue of Autonomic Neuroscience.