Johns Hopkins Vestibular NeuroEngineering Lab
What is vestibular sensation?
Normally, your inner ears measure how your head is oriented and how it is moving. That information - called vestibular sensation - drives reflexes that keep your eyes steady and allow you to walk without constantly devoting mental effort to avoiding a fall or veering off course. Most of the time, your vestibular system works entirely at a subconscious level. Since you don't normally perceive vestibular sensation as you do with other senses like sight, smell, hearing, touch and taste, you may be unaware of how different your life would be without it.
What happens if you lose vestibular sensation?
Without vestibular sensation in at least one ear, you would feel off balance all the time. You might feel a vague sense that your brain and eyes are floating in your head. Your vision would blur or jump during quick head movements, making it hard to see clearly enough to drive safely. Even if you're otherwise fit, you might need a walking stick to get around your neighborhood or workplace without falling. You might find it difficult to carry on a conversation while walking, because you are distracted by having to consciously monitor and guide every step. Navigating a crowded room or sidewalk would be disorienting. Walking in dim light or on uneven ground would pose a real threat of fall and injury. You might endure criticism for walking as if you're drunk, then find yourself socially isolated as you avoid situations that risk awkward and embarrassing interactions. Even family and friends who know you well might find it hard to understand your situation, because your deficit is invisible and most people are unfamiliar with vestibular disorders. They and you may wonder if your problem is "all in your head". Initially severe symptoms will improve over the first several months, as your brain develops workarounds to partly compensate for your vestibular loss, but you'll likely settle into a permanent state of feeling unsteady and unable to do things that used to be easy and automatic. You may feel anxious, depressed and hopeless.
What happens if your child is born without vestibular sensation?
Children who are born without vestibular sensation or lost it early in life are typically better than adults at learning to use vision or other senses to compensate for that loss, but they are slow to reach developmental milestones like sitting unassisted, standing and walking. When they do start sitting on their own, they may seem more wobbly than other children, as if their neck muscles are too weak to hold the head upright. Once they start walking, they can seem unusually clumsy. Learning to ride a bicycle or skateboard can be a frustrating and demoralizing experience. For kids who compensate so well that parents fail to detect other signs of vestibular loss, inability to see clearly during head movement can arise when they try to play tag, catch or sports. (Eye doctors can miss the diagnosis, because they typically only test vision with the head not moving.)
How is bilateral vestibular loss treated now?
You're likely to see at least a few doctors before eventually seeing someone familiar with bilateral vestibular loss. Some may prescribe a medicine (often meclizine or a sedative like Valium) that seems to help a little at first but ultimately makes you feel even more off balance. When you finally see a specialist familiar with bilateral vestibular loss (typically an otolaryngologist, neurologist or vestibular rehabilitation therapist in an academic medical center or highly specialized private practice focused on vestibular disorders), you're likely to leave feeling more down than hopeful after being told that apart from doing rehabilitation therapy exercises and stopping medicines that suppress vestibular function, there is no effective treatment for bilateral vestibular loss.
How common is this problem?
An estimated 2 million adults worldwide have symptoms typical of chronic severe bilateral vestibular loss, which is also called bilateral vestibular hypofunction or bilateral vestibulopathy. Since adults make up about 70% of the world population, about a million children probably also have this disorder. However, bilateral vestibular loss in children often goes unnoticed by parents and unreported by doctors, so high quality population-level data on bilateral vestibular loss in children are not yet available.
What is the Johns Hopkins Vestibular NeuroEngineering Lab doing about it?
We are advancing development of vestibular implant systems that can partly restore balance, stable vision and quality of life to individuals disabled by bilateral vestibular loss. Our approach combines neuroscience, biomedical/electrical engineering, computational modeling, epidemiology and clinical trial research. Since 2016, VNEL has been the site of the Multichannel Vestibular Implant Early Feasibility Study, which is the world's first and only clinical trial in which implant recipients use their vestibular implant systems at home, long-term and 24 hr/day or during all waking hours, as a sensory restoration treatment rather than solely for occasional measurements in a laboratory setting. In support of that effort, we have created and continue to refine new ways to measure vestibular function in humans and research animals; developed new techniques for enhancing outcomes of vestibular rehabilitation therapy; performed population-level studies to quantify how vestibular loss impacts our patients and society; and expanded the foundation of basic science upon which vestibular implant technology development depends.
What's a vestibular implant, and how does it work?
A vestibular implant system is a neuroelectronic prosthesis intended to generate artificial vestibular sensation when the inner ears cannot perform their normal role in detecting, measuring and reporting head motion to the brain. It works by continuously measuring head motion (using a sensor mounted in or on the head) and delivering electrical current pulses to the vestibular nerve (using an implanted stimulator that connects via wires to electrodes implanted in the inner ear near branches of the vestibular nerve). By varying the amplitude and rate of current pulses targeting different parts of the vestibular nerve, the implant system generates patterns of nerve activity that mimic the signals a normally-functioning inner ear would have sent to the brain. If that artificially-driven activity is similar enough to normal, the user's brain can use it to drive reflexes that keep the eyes and head steady, support the user's ability to walk without falling, and help the user accurately perceive head and body movement with respect to the surrounding world.
In many ways, vestibular implants are similar to cochlear implants, which are designed to partly restore hearing. Like cochlear implants, they include an external power and control unit and sensor (to provide energy and command signals to the rest of the system), an implanted stimulator (to receive commands and generate electrical pulses) and an array of electrodes in the inner ear (to deliver current to nearby neurons). Compared to cochlear implants, which are now a routine part of clinical practice at hundreds of centers worldwide and have been implanted nearly one million times over the past 50 years, vestibular implants a relatively new development. Including the individuals implanted at Johns Hopkins, only about 30 patients worldwide have undergone surgery to insert some version of a vestibular implant. This field is therefore still new and rapidly evolving.
What about gene therapy or other approaches to restoring vestibular sensation?
Our main focus is on vestibular implants using technology similar to the approach widely used for cochlear implants in routine clinical practice. However, we have explored other paths and will continue to do so whenever preliminary data suggest another way to reach our goal of restoring vestibular sensation to individuals disabled by bilateral vestibular loss. VNEL was one of four sites for the Novartis CGF166 trial, the world's first clinical trial of inner ear gene therapy, and we closely monitor on-going research elsewhere regarding inner ear gene therapy and stem cell treatments. We have explored laser/optical stimulation as an alternate means of exciting vestibular nerve activity. We collaborate closely with the Johns Hopkins Machine Biointerface Lab, which is leading development of a novel way to stimulate the nervous system using "Safe DC" current. We continue to develop and study novel approaches to vestibular rehabilitation, and we closely monitor work by colleagues worldwide who are leading parallel efforts. So far, none of these alternate approaches have yielded results sufficient to displace our core vestibular implant technology as the most promising approach to help our patients regain their balance, stable vision and quality of life.
Where can I learn more about the Vestibular NeuroEngineering Lab's vestibular implant trial?
Can I participate in the Vestibular NeuroEngineering Lab's vestibular implant trial?
How can I help support the Vestibular NeuroEngineering Lab's work?