ALKING ON OUR hind legs (and riding on two wheels) requires balance. Balance involves vision, muscle/tendon sense, pressure sensors in the skin, as well as the balance sensing organ (the labyrinth) in your inner ear.

Different conditions can affect our sense of balance, including problems with the balance organ, problems in the brain itself, systemic health problems, and problems with blood flow. The most common ones are those affecting the labyrinth, including Benign Positional Vertigo (BPV), Meniere's disease, labyrinthitis, vestibular neuronitis, and perilymph fistula.

The otolith organs, the saccule and utricle, have flat plates of gelatinous material with small, heavy calcium deposits called otoliths (Latin for "ear rocks") attached. When your head moves upward and downward (like in an elevator) the layer in the saccule moves; when you accelerate or decelerate, the layer in the utricle moves. These organs are also sensitive to head position, since tilting the head will cause the rocks to pull in a different direction (Yes, we've actually got rocks in our heads).

Here's how to do a Dix-Hallpike. Put a pillow on the middle of the bed so it's under your shoulders and your head hangs back at a 45° angle when you're lying down. Sit up in bed, turn your head 45° to the right, and while keeping your head to the right lie down quickly. Your head should stop tilted 45°

If this produces lots of dizziness and is associated with twitching of your eyes (have a friend watch) then the right posterior canal is probably where the rock is. If so, here's how to fix it. Note: Though this usually works, there are no guarantees. It's possible dizziness might worsen.

One of the most common causes of dizziness is associated with head motion: Benign Positional Vertigo (BPV). I've suffered from this myself, and it can make riding a bike, ummm, very interesting. Luckily, it can often be fixed.

Another common cause of balance loss, which is of more interest to us motorcyclists, is post-traumatic vertigo. (Note: Sometimes, this is caused by an inner ear fluid leak -- a perilymph fistula. Techniques described here won't work for this). After getting hit on the head, some people develop balance problems. I had a patient who'd rolled his pickup driving to the Burning Man Festival. Months later, he could only balance by holding on to the wall while walking. When he left my office half an hour later, he was cured. Here's how:

The labyrinth (balance organ)has two parts: The semicircular canals and the otolith organs (the saccule and the utricle). The semicircular canals sense rotation, and the saccule and utricle sense vertical and horizontal acceleration respectively. Both use sensitive hair cells, and both are filled with a fluid called endolymph. There are three semicircular canals in each inner ear. The canals are ring-shaped, and have a collection of hair cells in a swelling called the ampullu that sense motion as the fluid moves past them. Obviously, fluid moves at a different speed depending on the direction of the head motion relative to the plane of the canal. Since each of the three semi-circular canals in each inner ear is at right angles to each other, they can sense pitch, roll, and yaw. And since the right and left balance organs are at right angles, they're very sensitive in detectiong all head motions.

In Benign Positional Vertigo (BPV) one of the rocks gets loose and ends up in one of the semicircular canals. Some cases of post-traumatic vertigo happen for the same reason. Typically, the deposit will end up in the posterior canal, since it's the lowest one, hanging down like the trap in the drain under your kitchen sink. When there's a loose rock there, it affects the flow of fluid in that semi-circular canal which causes dizziness, with head motions, some more than others.

In BPV, head motion/turning causes dizziness; typically, lying down from a sitting position, especially with the head turned to one side. When we do this maneuver on the office, it's called a "Dix-Hallpike Test" and says whether you've got a loose rock in your head (so to speak). DFoing it tells docs if you've got BPV and how to fix it.

After lying back and getting the dizziness, keep your head tilted in the same direction for 30 to 60 seconds until the dizziness subsides. Then turn your head 90° to the left, still tilted back. Again, wait till the dizziness is gone, then turn another 90° left so you're looking down towards the floor. Hold until the dizziness stops, and then sit up.

Chances are pretty good that this will have rolled the otolith into an area where it won't cause dizziness. An illustration of this technique can be seen at http://www.tinyurl.com/6MVSE. (Note" I only recommend the Modified Epley Maneuvre.)

After doing this, you should not lie flat on your back for 48 hours. It's best to sleep in a recliner or propped up on pillows. Also, for a week, it's a good idea not to bend over all the way. Think of the rock as if it's sitting in a tumbler glued to the top of your head: Don't let it tip out. After a week it'll probably get stuck where it is, and won't cause problems.

If it doesn't work, it can be repeated a few times a day until better. This technique can cure over 90% of the cases of BPV.

One point: On occasion, the dizziness caused by this technique can cause nausea and even vomiting. Keep a barf bucket, paper towel, and a glass of water handy, just in case. And of course, don't do this right after an accident to a rider who is dizz: It's important to be sure there are no other injuries, like a neck fracture. But if you or a friend's been having head-motion dizziness for months to years, this might be the answer.