Aural vertigo comes in two flavors

By far the most common cause of inner-ear-related vertigo is BPPV, with brief spins brought on by lying down or rolling over in bed.  However, there are many other causes of vertigo, and it can be very confusing to figure out which one is the problem if you have something more complicated than BPPV.  One way to narrow this down is by looking at two very broad categories of vertigo, so that you can decide which of these you have.  This quickly helps you narrow down the diseases that may be affecting you. 

Read more: Aural vertigo comes in two flavors

Your brain creates the sensation of turning every time you move your head.  When you are not moving, each ear generates a low but steady flow of electrical signals that is received continuously by the brain.  This symmetric flow lets your brain know that your head is completely still.  If you move your head, the flow of signals changes instantly.  If you turn your head to the right, your right ear “turns on” and increases the flow of signals, while the left “turns off”, and shows a decrease. Your brain interprets this change in the symmetry of the signals as a turn—a right turn if the right ear is increased and the left ear is off, and a left turn if the left ear is increased while the right ear signals decline.  That’s what happens with normal head turns. 

Vertigo—the feeling of spinning when you are not turning—happens when the symmetry of the two ears is broken even though you are not moving, for example if one ear becomes turned on while the other is not.  This means there are two flavors of vertigo. The first flavor is vertigo brought on by an ear that suddenly gets turned on, increasing its signals.  If you are not turning, both ears should be sending the same low flow of signals, so if one suddenly starts firing more, this asymmetry will be felt as a turn toward the abnormal side. If your right ear suddenly increases its firing, you’ll feel spinning to the right. 

The second flavor of vertigo is spinning brought on by a sudden decrease in one ear’s signals—the ear turns off.  Again, the brain feels spinning any time there is asymmetry between the ears.  So, an ear that turns off makes the other ear’s signals look too fast, and you feel a spinning toward that normal ear.  A left ear that shuts off will cause a spinning feeling to the right for this reason.  Notice that a spin to the  right can come from EITHER the right ear being turned on or the left ear being turned off.  How can you tell whether it is due to an ear being stimulated vs. inhibited?

One way to determine this is to look at the speed of the feeling of spinning.  The key is that both ears have a fairly low flow of signals when you are not moving.  If you inhibit or turn off one of the ears, the other unaffected side does not increase—the flow is still fairly low from the good ear.  When your head is still, this will give you a constant, steady, unvarying feeling of spinning.  The room spins in a smooth fashion, not very fast.  You can usually still see things around you when having this vertigo, even though they will shift constantly.   Rather boring—the plain vanilla kind of vertigo.  You will be able to make this spinning increase by moving your eyes to one side, which is an important clue that you have one ear that is not working.  It will also worsen when you make a sudden head turn.

The situation is very different if you have one ear that becomes “too turned on”.   The natural sensor of the ear can sense extremely high rates of acceleration, so there’s no upper limit to the speed of the spinning you will feel. Fortunately, stimulatory vertigo is usually very short.  This is the flavor of vertigo caused by BPPV, when you directly stimulate one spinning sensor in your ear.  It’s not boring at all.  It’s thrilling (but not in a good way).  Not the sort of thing you can sleep through.  The world spins and it feels like you’re going to rocket off the bed.  How you move your eyes has no impact on this kind of vertigo. 

Here are some diseases that cause each flavor of vertigo:

Stimulatory vertigo—ear too turned on: BPPV, semicircular canal dehiscence, fistula

Inhibitory vertigo—ear turned off:  vestibular neuritis & viral infections, labyrinthitis, Meniere’s disease, autoimmune diseases, tumors such as acoustic neuroma, any loss of blood flow or trauma to the inner ear

It’s ironic that the most common cause of vertigo, BPPV, is stimulatory and so is more severe than the many other causes in the inhibitory category.  Mercifully, BPPV is short and easy to fix with maneuvers.