Leaping through the air with ease and spinning in place like tops, ballet dancers are visions of the human body in action at its most spectacular and controlled. Their brains, too, appear to be special, able to evade the dizziness that normally would result from rapid pirouettes. When compared with ordinary people's brains, researchers found in a study published early this year, parts of dancers' brains involved in the perception of spinning seem less sensitive, which may help them resist vertigo.
For millions of other people, it is their whole world, not themselves, that suddenly starts to whirl. Even the simplest task, like walking across the room, may become impossible when vertigo strikes, and the condition can last for months or years. Thirty-five percent of adults older than 39 in the U.S.—69 million people—experience vertigo at one time or another, often because of damage to parts of the inner ear that sense the body's position or to the nerve that transmits that information to the brain. Whereas drugs and physical therapy can help many, tens of thousands of people do not benefit from existing treatments. “Our patients with severe loss of balance have been told over and over again that there's nothing we can do for you,” says Charles Della Santina, an otolaryngologist who studies inner ear disorders and directs the Johns Hopkins Vestibular NeuroEngineering Laboratory.
Steve Bach's nightmare started in November 2013. The construction manager was at home in Parsippany, N.J. “All of a sudden the room was whipping around like a 78 record,” says Bach, now age 57. He was curled up on the living room floor in a fetal position when his daughter found him and called 911. He spent the next five days in the hospital. “Sitting up in bed,” he recalls, “was like sitting on top of a six-foot ladder.” Bach's doctors told him that his left inner ear had been inflamed by a viral infection. He underwent six months of physical therapy to train his brain and his healthy right ear to compensate for the lost function in his left. It helped, and he returned to his job in May 2014. Even so, this spring he was still having unsteady moments as he made his way around a construction site. “Whatever is in your brain that tells you when your foot is going to hit the ground to keep you upright, I don't have 100 percent of that,” he says. Vertigo can also trigger severe anxiety and depression, impair short-term memory, disrupt family life and derail careers.
Such crippling difficulties are prompting physicians to test new treatments for the most severe vertigo cases, Della Santina says. He is starting a clinical trial of prosthetic implants for the inner ear. Other doctors are experimenting with gene therapy to fix inner ear damage. And the work with dancers is beginning to reveal novel aspects of brain anatomy involved with balance, parts that could be targets for future treatments.
The ears are key to keeping us upright and stable because they hold an anatomical marvel known as the peripheral vestibular system. This is a tiny arrangement, in each ear, of fluid-filled loops, bulbs and microscopic hair cells. The hairs are topped by a membrane embedded with even tinier calcium carbonate crystals. When the head moves, the crystals pull on the hairs and combine with the other bits of anatomy to relay information about motion, direction and speed to the vestibular nerve. The nerve passes it on to a region at the stem of the brain called the cerebellum, as well as other neural areas. The brain then activates various muscles and the visual system to maintain balance.
The list of things that can go wrong with this delicate system is long. Causes of inner ear vertigo include tumors, bacterial and viral infections, damage from certain antibiotics, and Meniere's disease, a chronic condition characterized by recurring bouts of vertigo, hearing loss and tinnitus that experts estimate to affect an additional five million people. The most common vestibular disorder is benign paroxysmal positional vertigo, or BPPV. It occurs when renegade crystals get loose, float into the vestibular loops and generate a false sensation of movement. Fortunately, this type of problem is usually treated effectively with physical therapy involving a repeated set of slow head movements that float the crystals out of the loops.
But physical therapy does not help everyone or, as in Bach's case, does not heal the person completely. Some patients have lost vestibular function in both ears. For them, Della Santina and his colleagues at Johns Hopkins have been developing an implant that substitutes mechanical components for damaged inner ear anatomy. Once the researchers get the green light from the U.S. Food and Drug Administration, they will begin testing their invention, called a multichannel vestibular implant, in humans. The device is modeled on the cochlear implants that have restored hearing for thousands of people since the first one was used in 1982. These implants use a microphone to pick up sound vibrations and transmit them to the brain via the auditory nerve. Instead of a microphone, a vestibular implant has two miniature motion sensors that track the movement of the head. One, a gyroscope, measures the motion of the head as a person looks up, down and around a room. The other, a linear accelerometer, measures directional movement, such as walking straight ahead or down a flight of stairs. And instead of breaking sound into different frequency components and sending them to the auditory nerve, the motion sensors send the signals connoting head position and movement to the vestibular nerve.
Results from the trial of a different vestibular implant in four patients with Meniere's disease at the University of Washington were mixed. Although it worked well initially, the effect petered out after a few months. But the Johns Hopkins device has a different design and will be used in patients with disorders other than Meniere's, so the physicians hope the outcomes will be better.
Another strategy being tested in humans involves a gene that controls hair cell growth in the inner ear. During embryonic development, the ATOH1 gene directs the creation of these cells, which are crucial for hearing and balance. The gene stops working at birth, leaving humans with a fixed number of hairs—and problems if the hairs are damaged. In an early FDA-approved clinical trial targeting balance and hearing, researchers led by Hinrich Staecker, an otolaryngologist at the University of Kansas, are injecting the gene into the ears of 45 patients with severe hearing loss, under general anesthesia. In experiments on mice with severe inner ear damage, the compound restored hair cell levels to 50 percent of normal, with some improvement in hearing. If the experimental compound, called CGF166, has similar effects in people, it could launch a new era in the treatment of vestibular disorders.
Gene therapy needs to be handled carefully; it can trigger serious immune system reactions, and patients in other experiments have died. Safety factors in this trial include a gene that can be turned on only in the targeted cells, Staecker says, and a minuscule dose that does not circulate through the body. In addition, he explains, the viral jacket around the gene, which helps it penetrate cells, has been deployed “without safety problems” in about 1,500 people in previous experiments with different genes.
Even if such research succeeds, major gaps in our basic knowledge about disabling dizziness remain. For example, doctors do not know why the ear crystals get loose in the first place. These gaps are why some researchers turned to ballet dancers. The idea is to study especially robust vestibular systems to better understand the mysteries of unhealthy ones.
A team at Imperial College London used a battery of tests and brain imaging to investigate the ability of expert ballet dancers to resist vertigo while performing multiple pirouettes. The scientists studied 29 female dancers with an average of 16 years of training—the dancers started at or before age six—and compared them with female rowers. The more experienced and highly trained dancers had a lower density of neurons in parts of the cerebellum where dizziness is perceived, the group reported this year in the journal Cerebral Cortex. The anatomy is smaller, the researchers think, because the dancers continually suppress the perception of dizziness. During pirouettes, dancers focus their eyes on a fixed point for as long as possible. The technique, called spotting, limits the sensory signals sent to the brain. This “active effort to resist dizziness” during years of training also left the dancers in the study with a smaller, slower network of neuron connections in a part of the right hemisphere of the brain where those signals are processed.
This kind of suppression might someday offer relief to patients with chronic vertigo, if ways can be found to develop it in nondancers using physical therapy, the scientists suggest. For thousands of patients, it would be a turn for the better.