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NIH 1998 Almanac/The Organization/NIDCD/      

National Institute on Deafness and Other Communication Disorders : Research Programs


Research programs at NIDCD are intended to improve methods of prevention, diagnosis, treatment, and rehabilitation of clinical problems of deafness and other communication disorders.

The Division of Intramural Research of NIDCD conducts basic and clinical research in human communication research, which is within the purview of the institute. Research objectives include studies of electromechanical processes responsible for fine tuning in the cochlea; electromotility of the outer hair cell; molecular bases of mechano-sensory transduction mechanisms in the organ of Corti; molecular bases for G-protein signaling with emphasis on sensory signaling processes in the chemical senses; development of vaccines for otitis media; molecular mechanisms underlying the development and function of the mammalian olfactory system; mechanisms responsible for the development of the inner ear; identification, characterization and cloning of genes responsible for hereditary hearing impairment; molecular mechanisms underlying auditory system function with emphasis on neurotransmission and neuromodulation; identification of genes associated with neoplasms affecting human communication; identification of the genetic component of stuttering; neuroimaging of brain function in physiologic and pathophysiologic states; pathophysiology and etiology of voice and speech disorders; and epidemiological and biometric research studies of communication disorders.

Hearing

The fields of cellular and molecular biology have furthered hearing research. A multitude of genes for syndromic and nonsyndromic forms of hearing impairment including autosomal dominant and recessive, X-linked and mitochondrial modes of transmission have been located in specific regions of the human genome. In addition, several clinically relevant genes essential for normal auditory development and/or function have been cloned.

Other cochlear-specific genes have been isolated from enriched membranous labyrinth cDNA libraries. New technology, including the development of detailed maps of expressed sequence tags (EST) coupled with the use of inner ear specific cDNA libraries, exon trapping and cDNA library enrichment procedures, will facilitate gene cloning. Once cloned, the molecular biology of hearing and the role of particular proteins in the development and/or maintenance of the inner ear can be determined.

These advances offer researchers many opportunities to study the characteristics of deafness, hereditary factors involved in hearing loss, and genes that are critical for the development and maintenance of the human ear. Scientific advances have also been translated into cochlear implants, digital hearing aids, and tactile devices that provide information by stimulating the skin.

Great strides are being made in the study of properties of auditory sensory cells, and of characteristics of the response of the inner ear to sound. Research has verified that despite substantial variability in the performance of children who have received cochlear implants, most demonstrate an improvement in speech perception and production. Speech produced by children who use multichannel cochlear implants is usually more accurate than the speech produced by children with comparable hearing impairment using vibrotactile devices or hearing aids. Cochlear implants also positively influence children’s receptive and expressive language skills. The longer children use their implants, the greater their language ability.

To achieve the most benefit from their implants, however, children generally need extensive oral-auditory training following implantation and also benefit from periodic audiological assessments. Cochlear implants have benefited children who are congenitally deaf as well as those who are postlingually deaf. The vast majority of adult implant recipients derive substantial benefit in conjunction with speechreading, and many can communicate effectively without speechreading and are able to communicate by telephone. Dedication to research on cochlear implants throughout the world will improve the capabilities of current implant users and improve our understanding of the auditory system.

New insights have been gained concerning the encoding of complex signals transmitted from the auditory nerve to the brain. The relationship between the neural codes for sound intensity, frequency, duration and temporal characteristics of auditory signals and the perception of the stimulus variables has been further clarified. Valuable progress has been made in understanding the structure and function of efferent feedback pathways to the inner and middle ear. There is now good evidence that this system may aid in the detection of signals in noisy environments and serve to protect the ear from acoustic injury.

Gains have been made about the ways in which the brain creates maps of auditory space and how the maps interact with visual space. This research may have implications in treatment of children who acquire hearing loss in infancy or early childhood. Further, psychoacoustic and electrophysiologic studies of infants and children are providing important new insights into the development of functional hearing.

In the aging auditory system, discoveries have been made demonstrating changes in the regulation of fluid composition and autoregu-lation of cochlear blood flow whcih may underlie some of the biologic effects of aging on auditory function. Improved behavioral and electrophysiological techniques for measuring auditory function are providing more accurate assessments of the peripheral and central components of age-related hearing impairment.

Recent development of animal models for bacterial and viral infections hold promise for new diagnostic and therapeutic approaches to sensorineural hearing loss caused by infections. Antiviral drugs may find rapid application in the treatment for these conditions with the advent of suitable animal models in which to test efficacy. In addition, models will allow a greater understanding of why and to what degree infants and children are susceptible to ototoxic drugs used in the treatment of infections.

Otitis media continues to be a significant focus of research because of its prevalence and cost to society. Important risk factors have been identified. Studies of the eustachian tubes have provided new information on tubal mechanics, surfactant-like (fluid) substances and middle ear pressure regulation. Progress has been made toward defining the role that viruses may play in otitis media and the cellular and molecular changes that occur during viral and bacterial infection of the middle ear.

Balance

NIDCD supports research on balance and the vestibular system. Balance disorders afflict a large proportion of the population, particularly the elderly. The vestibular system, with its receptor organs located in the inner ear, plays an important role in the maintenance of one’s orientation in space, balance, posture and visual fixation of objects during motion and regulation of locomotion and other volitional movements. Vestibular disorders can, therefore, yield symptoms of imbalance, vertigo (the illusion of motion), disorientation, instability, falling, and visual blurring (particularly during motion). Major disorders affecting the vestibular system result from infection, trauma, impaired blood supply, impaired metabolic function and tumors.

In addition to its roles in the stabilization of gaze and balance, recent findings suggest that the vestibular system plays an important role in regulating blood pressure. This information holds potential clinical relevance to the understanding and management of orthostatic hypotension (lowered blood pressure related to a change in body posture).

The institute supports research to develop and refine tests of balance and vestibular function. Computer-controlled systems measuring responses activated by stimulating specific parts of the vestibular sense organ are now available. Improved tests of functional disability will have important implications for planning programs of physical rehabilitation for patients with balance and vestibular disorders.

Smell and Taste

NIDCD investigators study the chemical senses of smell and taste to enhance understanding of how individuals communicate with their environment. For example, this research is providing insight into changing preferences and aversions for specific foods and flavors. Improved understanding of the interaction between chemoreception and food consumption will lead to improved nutrition from birth to old age.

Both the olfactory and gustatory systems offer special approaches for understanding fundamental mechanisms of plasticity. NIDCD scientists have found that smell and taste cells have the capacity to replace themselves throughout life. These are the only known mammalian sensory cells with this property.

Advances in molecular and cellular biology, biophysics and biochemistry of the olfactory and gustatory systems are paving the way for improved diagnosis, prevention, and treatment of chemosensory disorders. The vertebrate olfactory receptor neuron has become an important biologic model system in molecular and cellular biology. The olfactory receptor gene family was recently described in mammals and may contain as many as 1,000 olfactory receptor genes. NIDCD scientists are presently characterizing genetic mechanisms of olfaction which will provide the opportunity to study the molecular pharmacology of the process of smell. In addition, the use of available biochemical and molecular probes will lead to a more complete characterization of neurotransmitters throughout the gustatory system.

Voice, Speech and Language

Studies of voice and speech disorders are aimed at determining the nature, causes, treatment and prevention disorders such as stuttering, spasmodic dysphonia, and dysarthria. A recent study has demonstrated a new, effective treatment for one such disorder, spasmodic dysphonia--a hyperactivity of the muscles of the larynx which constricts the vocal folds and severely distorts speech. This treatment involves injection of minute amounts of botulinum toxin into laryngeal muscles. The toxin blocks muscle stimulation and eliminates hyperactivity, rendering a patient free of the symptoms for as long as 4 months.

Oral speech communication may not be a realistic option for individuals with severe dysarthria. Substantial progress has been made in the development of augmentative communication devices to facilitate the expressive communication of persons with severe communication disabilities. An investigation of conversational performance by augmentative communicative device users is in progress. Other funded research evaluates whether a low-cost, laser-activated keyboard for accessing personal computers is feasible. By providing access to computers, individuals with disabilities can immediately use personal computer software programs and speech synthesizers for augmentative communication.

Language research continues to expand the understanding of the role of each hemisphere of the brain in communication and language, of early specialization of the brain, and of the recovery process following brain damage. This research is intended to further understanding of the neural bases of language disorders. Research on acquistion, characterization and utilization of American Sign Language is expanding knowledge of the language of people who are deaf.


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