Exploring the relationship between the vestibular system, cognitive impairments and sensorimotor behaviors

Every year, nearly 25-50% of older adults fall.

It’s a statistic vestibular researchers like Dr. Megan Kobel knows well.

Kobel, an assistant professor in the Department of Speech, Language, and Hearing Sciences at the University of Arizona and the director of the NIH-funded Vestibular Research Lab, has dedicated her career to treating vestibular disorders, and uncovering the relationship between the vestibular system, cognitive impairments and sensorimotor behaviors.

The goal of the research, Kobel said, is to better understand the fundamental mechanisms underlying fall risk, and to help determine why patients with Alzheimer’s disease and other cognitive impairments are more likely to lose their balance and fall down than cognitively healthy adults. Kobel’s research also seeks to examine why patients with vestibular dysfunction exhibit subsequent changes in cognition.

“The factors contributing to fall risk are not completely understood,” Kobel explained. “The vestibular system, part of the inner ear, is a known contributor to fall risk, and recent evidence suggests that cognition may interact with vestibular function to influence falls.” 

Because the vestibular system is responsible for sensing motion, patients with vestibular disease often experience balance problems, dizziness, vertigo, along with many other symptoms, which lead to increased likelihood of falls.

To Kobel, one of the most pressing concerns in vestibular research is how to improve diagnosis for patients with vestibular symptoms.

“Over a third of patients who we see in clinic have test results come back normal, but we know that there's an abnormality there,” she said. “We are fundamentally missing something in a lot of patients.”

According to Kobel, it was this disparity that initially motivated her to pursue a PhD. Since then, her work has been focused on advancing vestibular diagnostic techniques and assessing vestibular perception- or- how we sense and feel motion.

“Traditionally, when we do vestibular testing, we measure a bunch of reflexes, and then we try to figure out what's going on,” Kobel said.

But thanks to grant funding from the National Institutes of Health, Kobel is bringing new, state of the art diagnostic equipment to the University of Arizona.

The “six degree of freedom motion hexapod,” which Kobel said is expected to be fully operational in the next few weeks, will help Kobel, and other vestibular researchers to better understand abnormalities in patients with known or suspected vestibular disorders.

When using the hexapod, patients are placed on a platform which can be maneuvered in six different directions- up and down, back and forward, and side to side- giving the machine its name.

“It can go in any direction you want or any combination of directions you want,” Kobel said. “We use it to figure out the smallest motion that people can correctly identify. In patients with dizziness that tends to better correspond to their symptoms, and then in older adults we’re able to detect abnormalities that better correspond to their balance and walking problems.”

By collecting data on healthy adults, adults with vestibular disorders, and adults with cognitive impairment, Kobel said her research will further explore the extent to which the inner ear, balance, and cognition are interrelated.

“We know that in adults or even children with inner ear disorders, we can see changes in cognition. On the standard cognitive tests, and on tests of spatial cognition, they tend to do worse than healthy adults with healthy inner ears.”

Similarly, Kobel said that adults with mild cognitive impairment and Alzheimer's disease, have about two to three times the incidence of vestibular disorders in comparison to cognitively healthy adults.

She believes that understanding these correlations, can lead to better treatments, and better outcomes for patients living with vestibular disorders or cognitive impairment.

“We know, in older adults with cognitive impairment, a fall is the number one predictor of loss of independence,” Kobel said. “So being able to figure out which adults are at high risk of falling means that we could potentially intervene sooner.”

The hope, she said, is that researchers would be able to use the hexapod to potentially track a patient's motion perception changes, and monitor their progress over time.

“Right now, we only track patient recovery through their symptom reports,” Kobel said. “It’s based on how they think they're doing, but we have nothing to back that up. We have no test to confirm they’re doing better.”

In the future, Kobel said the hexapod could provide those answers, and even open up valuable new avenues of research. Currently, Kobel said she is working to develop methods to measure and improve balance performance in vestibular patients, which will utilize the hexapod as a new form of treatment.

“Long term, we might be able to develop treatments that lead to better balance performance,” she said. “We could design it to use virtual reality and motion paired together, or we could introduce some conflicts and see how people handle the motion processing. Over time, with a lot of practice, we might be able to improve their motion perception.”