Dan Hixson/University of Utah College of Engineering

University of Utah biomedical engineering Professor Richard Rabbitt (left) and doctoral student Marta Iversen have discovered why certain people experience dizziness when they hear a particular sound, such as a musical tone.

For people suffering from Tullio phenomena, a sound, a song or even a cough can cause dizziness, vertigo, nausea and involuntary eye movements. Now, a study in Nature's online open access journal, Scientific Reports, explains the process behind the problem.

Humans avoid dizziness when moving or looking around because our eyes reflexively move to compensate when the fluid in our ears' semicircular canals detects motion.

In canal dehiscence syndrome, a hole or thinning in the canal's bony exterior confuses this vestibulo-ocular reflex.

University of Utah biomedical engineer Rick Rabbitt and colleagues at UT, University of Mississippi Medical Center in Jackson and Johns Hopkins University School of Medicine in Baltimore found that this opening let a pressure wave fool the canals' hair cells into thinking the head is in motion.

"The sound induces waves in the inner ear. Those waves then deflect the hair cells. The hair cells then send a signal to the brain. The brain relates that to the muscles that are connected to the eyes, and it makes the eyes move," Rabbitt said.

In other words, the patient sees the world spinning because their eyes are in motion, not their head.

Such eye movements can also result from atmospheric pressure changes or heartbeat-induced variations in blood pressure.

Earlier work established that a hole or thinning in the bone enclosing the inner ear's semicircular canals caused the problem, and thereby enabled surgical treatments. But the specific mechanism at work remained a mystery.

To solve it, the team developed a computer model of the inner ear to better understand the biomechanics at work, and made observations of neural activity and fluid motion in oyster toadfish (Opsanus tau).

Researchers utilize the species while studying vestibular system disorders because its balance and orientation system resembles that of humans. For example, two oyster toadfish accompanied John Glen on his 1998 space shuttle mission, where they contributed to understanding how astronauts' inner ears adjust to microgravity.