Research & Clinical Trials
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Research in animal models of deafness at birth provide insights into a broad spectrum of circumstances that affect brain structure and function, particularly as related to a child's ability to learn through developmental stages.We have examined the role that deafness plays in changing the connections within the hearing pathway. We have examined the notion of a "critical period" during which the brain can use restored hearing to open a window of opportunity for refined use of spoken language. Our results suggest that neural connections appear structurally normal very early in life, then begin deafness-induced changes in the pattern of contact between auditory cells in the brain. Research utilizing cochlear implants in animal models has demonstrated the ability to reverse deafness-induced changes in nerves that are critical to introducing activity into the hearing pathway.
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The Cochlear Implant Center tracks educational progress of children with a cochlear implant by using an educational resource matrix (ERM). The matrix was developed on the basis of observations that movement into a mainstream classroom setting is often accompanied by an initial increase in the need for support services, such as interpreters and speech-language therapists. Follow up of school-aged children with implants indicates that these children participate in mainstream education at a substantially higher rate and require diminishing levels of support services than children with similar hearing who use hearing aids. Long-term tracking of educational outcomes of implanted children continues as part of an ongoing assessment of cochlear implant rehabilitation.
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Evaluation of the effectiveness of the cochlear implant in children has largely focused on the perception of speech and on language performance in standardized tests. Because the ultimate goal of cochlear implantation is to facilitate the use of spoken language, there is a clear need to evaluate the strategies adopted by implanted children in spontaneous communication. This information can also guide therapy to promote language learning.
To expand on our assessment of the implant experience in young children, The Cochlear Implant Center has developed a method of video analysis that assesses emerging language even in very young children for whom standardized tests are not useful. Results reveal significant gains in language acquisition in implanted children, who have nearly triple the rate of expressive vocabulary growth compared to children using hearing aids.
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The combination of earlier identification of hearing loss and access to early cochlear implantation has sparked an interest in results in terms of education, economics, emotional development, and cultural effects. The Cochlear Implant Center is studying the emergence of one important aspect of educational success - reading. Our studies are investigating the methods by which newly restored access to all of the frequencies of speech sounds contained in words can be used to generate opportunities to acquire the skills needed to become effective readers.
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The Cochlear Implant Center leads a large multicenter study of the impact of early cochlear implantation on childhood development. The Childhood Development after Cochlear Implantation (CDaCI) study is funded by the NIH. The goal of this longitudinal study is to determine the predictive value of variables as they relate to communication, behavior and educational outcomes of cochlear implantation in young children. The CDaCI study addresses the complexity of language development under conditions of restored hearing in the very young child when a variety of operational skills develop rapidly. The CDaCI study is also helping to determine the impact of medical and hearing assessment tools and parent-child interactions on levels of spoken language, speech recognition, selective attention, psychosocial developmental milestones, and quality of life attained with early cochlear implantation.
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In addition to speech, the cochlear implant is capable of transmitting other complex sounds. The Cochlear Implant Center has been involved in collaborative research with the National Institutes of Health (NIH) in investigating how the cochlear implant conveys the complex information contained by music. By studying patterns of brain activity, it may be possible to design improved methods of encoding sound and training strategies to provide a fuller appreciation of the complex sounds contained in speech and music.
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Like hearing, the sense of balance is based in the ear. Children and adults with severe hearing loss occasionally experience dizziness, vertigo or imbalance before or after cochlear implantation. Extended periods of vertigo and imbalance are rare but, when present, are treatable with exercise programs designed to elicit the brain's natural corrective mechanisms. Research by The Cochlear Implant Center has led to the development of diagnostic tests and treatment approaches that can limit the risk of balance disorders and help guide the choice or ear for cochlear implantation.
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Johns Hopkins outcomes studies have assessed the impact on overall health and quality of life to determine the real-life benefit provided by cochlear implants. Implant users surveyed before and after their operation report dramatic results. These appraisals indicate that the cochlear implant ranks extremely high in the positive impact it has on quality of life and cost-effectiveness. A prospective study of vestibular implantation using the model established by the Cochlear Implant Center cochlear implant studies revealed that vestibular implantation is also likely to be highly cost-effective.
Laboratories Affiliated with The Cochlear Implant Center
Auditory Brainstem Laboratory
The overall goal of the Auditory Brainstem Library is to understand how abnormal auditory input from the ear affects the brainstem, and how the brain in turn affects activity in the ear through efferent feedback loops. Our emphasis is on understanding the effects of different forms of acquired hearing loss (genetic, conductive, noise-induced, age-related, traumatic brain injury-related) and environmental noise. We are particularly interested in plastic changes in the brain that compensate for some aspects of altered auditory input, and how those changes relate to central auditory processing deficits, tinnitus, and hyperacusis. Understanding these changes will help refine therapeutic strategies and identify new targets for treatment. We collaborate with other labs in the Depts. of Otolaryngology, Neuroscience, Neuropathology, the Wilmer Eye Institute, and the Applied Physics Laboratory at Johns Hopkins, in addition to labs outside the university to increase the impact and clinical relevance of our research.
Principal Investigator: Amanda Lauer, Ph.D., M.S.
Bowditch Research Group
Bowditch Research Group conducts research regarding speech discrimination in background noise, cochlear implants and osseointegrated hearing devices.
Principal Investigator: Stephen Bowditch, Au.D., M.S.
Carey Research Group
John Carey’s Research Group conducts research regarding diseases of the inner ear that affect both balance and hearing mechanisms. Key interests include superior semicircular canal dehiscence syndrome (SCDS), the normal vestibular reflexes and how they change with age, novel intratympanic treatments (i.e., middle ear injections) for conditions like Menière’s disease and sudden hearing loss, and the mechanisms of vestibular migraine. With Lloyd Minor, Dr. Carey helped develop the operation to repair the superior canal in patients with SCDS using image-guided surgery. Dr. Carey has been funded by the National Institutes of Health – National Institute on Deafness and Other Communication Disorders to study inner ear balance function in Menière’s disease and steroid treatment of sudden hearing loss.
Principal Investigator: John Carey, M.D.
Glowatzki Lab
Research in the Glowatzki Lab focuses on the auditory system, with a particular focus on synaptic transmission in the inner ear.
Our lab is using dendritic patch clamp recordings to examine mechanisms of synaptic transmission at this first, critical synapse in the auditory pathway. With this technique, we can diagnose the molecular mechanisms of transmitter release at uniquely high resolution (this is the sole input to each afferent neuron), and relate them directly to the rich knowledge base of auditory signaling by single afferent neurons.
We study pre- and post-synaptic mechanisms that determine auditory nerve fiber properties. This approach will help to study general principles of synaptic transmission and specifically to identify the molecular substrates for inherited auditory neuropathies and other cochlear dysfunctions.
Principal Investigator: Elisabeth Glowatzki, Ph.D.
Vestibular NeuroEngineering Lab
Research in the Vestibular NeuroEngineering Lab (VNEL) focuses on restoring inner ear function through “bionic” electrical stimulation, inner ear gene therapy, and enhancing the central nervous system’s ability to learn ways to use sensory input from a damaged inner ear. VNEL research involves basic and applied neurophysiology, biomedical engineering, clinical investigation and population-based epidemiologic studies.
Principal Investigator: Charles Della Santina, M.D., Ph.D.
