A New Window on the Inner Ear
The inner ear is the central element in the vestibular system, used for maintaining a sense of balance. But like the “sixth sense,” what’s going on in the inner ear—and why someone’s sense of balance might go awry—often remains an enigma. Hiding behind a stronghold of hard bone, this tiny piece of anatomy is extremely difficult to see, even with surgery. To diagnose diseases of the inner ear usually involves an intense examination of the bones in this structure during an autopsy, not much help to their original owner.
But Otolaryngology–Head and Neck Surgery resident Bryan Ward is leading research that’s shining a new light on how the inner ear works, providing insight that could eventually help people with inner ear problems.
Ward’s work builds on a discovery that Johns Hopkins scientists Dale Roberts and David Zee, both in the Department of Neurology, made several years ago. The team was trying to figure out why many people undergoing magnetic resonance imaging (MRI) get vertigo while inside or coming out of the machine. Their findings suggested that the strong magnet in an MRI machine pushes on fluid that circulates in the inner ear, leading to a feeling of unexpected or unsteady movement.
Like most good research, these findings led to even more questions. Those researchers discovered that the eyes of people in the MRI machine had rapid, involuntary movements called nystagmus. Although these movements were different between people who had healthy inner ears and those with inner ear problems, not enough is yet known to use MRI to diagnose different inner ear diseases. In that same vein, if researchers knew more about how MRI affected inner ear function, they might be able to use this tool to test out new treatments for balance problems.
To further this research, Ward is relying on one of the most powerful tools of biomedical research: animal models.
“Mice are used in a lot of basic research because their anatomy and physiology are a lot like humans’,” Ward explains. “Their inner ears are no exception.”
Working with mice in a tiny MRI machine, Ward and his colleagues have discovered that mice also experience nystagmus, although their eye movements are much faster—a reflection of the strength of the MRI’s magnet on their smaller inner ear anatomy. Since mice can be bred to mimic the multitude of ways that inner ears can go wrong in humans, Ward says, studying these animals in the MRI can give a wealth of insight on how different inner ear problems might be reflected in eye movements. They’re conducting those experiments now, sorting out how the eye movements of mice with different mutations that affect the inner ear differ from those of normal, healthy mice.
They’re also testing another animal model whose inner ear is surprisingly like ours: the zebrafish. Because zebrafish multiply quickly and can have all the same inner ear problems as mice and people, Ward explains, they could be incredibly useful for testing drugs to treat inner ear diseases. Sure enough, Ward and his colleagues found that zebrafish also behave differently during MRI, tilting or swimming in a corkscrew, which suggests that they might be feeling vertigo as well.
Eventually, Ward hopes, these animal studies will make the inner ear less of a mystery—making his work treating patients with dizziness and balance problems even more effective.