Cochlear Mechanisms Of Otoacoustic Emission Generation
Funder
National Health and Medical Research Council
Funding Amount
$311,989.00
Summary
Deafness, both congenital and acquired, is likely to be one of the major causes of disability in the Australian workforce, in young Australians, and in some categories of pre-term infants in the next decade or two. While not life-threatening, hearing impairment deprives individuals of one of their most basic social needs: the ability to communicate with others. Although little can be done to recover lost hearing, it is important to detect hearing loss as early as possible in order to reduce furt ....Deafness, both congenital and acquired, is likely to be one of the major causes of disability in the Australian workforce, in young Australians, and in some categories of pre-term infants in the next decade or two. While not life-threatening, hearing impairment deprives individuals of one of their most basic social needs: the ability to communicate with others. Although little can be done to recover lost hearing, it is important to detect hearing loss as early as possible in order to reduce further loss (by behaviour modification in the case of noise-exposed adults) and to provide hearing assistance in very young children so that they may be exposed to some degree of auditory experience at as early an age as possible. To this end, the phenomenon of otoacoustic emissions, or noises from the ear, now recognised for twenty years, is likely to become even more significant in the early years of the next millennium. Otoacoustic emissions were first demonstrated as very soft echoes re-emerging from the ear after a delay of ten milliseconds or so following a click stimulus. These echoes are sounds produced by the ear as it goes about its normal function and are lost if the hearing sensitivity of the individual is below normal. Several other forms of otoacoustic emissions have been discovered and rapidly applied to the testing of hearing so that today the technique of assessing hearing status in neonates and others unable to co-operate, as well as in diagnostic applications, is widespread. The application of the technique, however, has preceded a real understanding of what otoacoustic emissions are and how they are generated, and their widespread use at the moment is somewhat akin to a car repair industry which does not understand how an engine works. This proposal intends to investigate the basic mechanisms behind otoacoustic emissions in order to improve their efficiency and accuracy of clinical interpretation.Read moreRead less
Normal hearing relies on the generation and transmission of electrical signals in the hearing organ, the inner ear. These electrical signals are generated by the action of specialized molecular ion channels in the cellular membranes of the inner ear and this research aims to charcterize these ion channels and detail their role in the hearing process. The results will impact on our understanding of human hearing disorders such as tinnitus, auditory neuropathy and disturbances of loudness sensatio ....Normal hearing relies on the generation and transmission of electrical signals in the hearing organ, the inner ear. These electrical signals are generated by the action of specialized molecular ion channels in the cellular membranes of the inner ear and this research aims to charcterize these ion channels and detail their role in the hearing process. The results will impact on our understanding of human hearing disorders such as tinnitus, auditory neuropathy and disturbances of loudness sensation.Read moreRead less
Thalamic And Basal Forebrain Contributions To Auditory Cortical Reorganization Produced By Partial Hearing Loss
Funder
National Health and Medical Research Council
Funding Amount
$364,768.00
Summary
When part of the cochlea is damaged in adult animals, leading to a partial hearing loss, the auditory area of the cerebral cortex reorganizes itself, so that the area deprived of input by the peripheral lesion is not silent, but is occupied by expanded representations of adjacent frequencies. This reorganization has been observed in a number of species, including non-human primates, and it seems likely that it also occurs in humans with cochlear damage and hearing loss of this sort. If it does, ....When part of the cochlea is damaged in adult animals, leading to a partial hearing loss, the auditory area of the cerebral cortex reorganizes itself, so that the area deprived of input by the peripheral lesion is not silent, but is occupied by expanded representations of adjacent frequencies. This reorganization has been observed in a number of species, including non-human primates, and it seems likely that it also occurs in humans with cochlear damage and hearing loss of this sort. If it does, it would have important consequences for the way in which input from a hearing aid or cochlear prosthesis (bionic ear) is processed in the brain. This Project is designed to clarify the nature of the systems in the brain that contribute to this form of cortical plasticity, using an animal model. One aim is to determine whether the plasticity is intrinsic to the cortex or occurs in the pathways over which information is conveyed to the cortex. This will be assessed by determining whether such plasticity is also found in the auditory thalamus, the final subcortical auditory nucleus from which information is sent to the cortex. The second aim is to determine whether the occurrence of plasticity is controlled by modulatory influences from the basal part of the forebrain. Neurons in this area project to many parts of the cortex, and evidence from other sensory systems suggests that these projections exert a permissive function, allowing the cortex to reorganize when input is altered. This aim will be pursued by determining whether cortical reorganization occurs after hearing loss when this basal forebrain system is inactivated. The significance of these studies is that they will elucidate the way in which the brain reorganizes itself when it is confronted with altered input. This information is important for our understanding of normal auditory information processing mechanisms and of the way in which input from prosthetic devices is processed in the hearing-impaired.Read moreRead less
NEURAL MODULATION OF HEARING LOSSES INDUCED BY LOUD SOUND
Funder
National Health and Medical Research Council
Funding Amount
$290,500.00
Summary
Loud sounds, from occupational and recreational sources, are the most common threat to hearing and can result in temporary hearing losses (as might be experienced after an evening at a noisy pub or concert) or permanent hearing losses (after prolonged or multiple loud sounds, as for example in a noisy work environment). Noise reduction programs are either not always possible or effectively applied. A parallel strategy is the study of biological mechanisms that may ameliorate hearing damage, with ....Loud sounds, from occupational and recreational sources, are the most common threat to hearing and can result in temporary hearing losses (as might be experienced after an evening at a noisy pub or concert) or permanent hearing losses (after prolonged or multiple loud sounds, as for example in a noisy work environment). Noise reduction programs are either not always possible or effectively applied. A parallel strategy is the study of biological mechanisms that may ameliorate hearing damage, with a view to optimising such mechanisms. I propose to build on seminal Australian work to examine how one such system, nerves from the brain to the inner ear (the site of most damage from loud sounds), modulates hearing losses caused by loud sounds. Early studies indicated these nerves could protect from damage induced by short-lasting loud sound and this has led to international interest in functional applications of such protection to reduce hearing damage suffered by humans. However, my recent work indicates the nerves exert complex protective and exacerbative effects to loud sounds similar to common trauma or occurring under conditions similar to common trauma. They even exacerbate hearing losses due to loud sound, especially when there is an imbalance in hearing sensitivity in the two ears (bilateral) similar to what is common in humans. These findings make it critical that functional application be delayed until the full range of effects exerted by the nerves is understood. I propose to elucidate the novel complex effects of these nerves to loud sound. Specific aims are: (1) To understand effects of these pathways to loud sounds like those encountered by humans, (2) To investigate how chronic imbalanced bilateral hearing sensitivity, like that common in humans, alters effects of the nerves and when they change from being protective to exacerbative, (3) To adduce how an atraumatic sound affects hearing losses due to later loud sound and the role played by these nerves.Read moreRead less
Reflex Control Of Human Jaw Muscles By Periodontal Mechanoreceptors
Funder
National Health and Medical Research Council
Funding Amount
$405,173.00
Summary
An understanding of the functional connection between the jaw muscles and various receptor organs in and around the mouth is necessary to elucidate the process of chewing and its underlying rules. Unless the details of this functional connection in health and disease are thoroughly understood, the diagnosis and treatment of chewing related disorders will remain at the present state. For example: a We still do not know why chewing in edentulous subjects is less efficient and why the bite forces i ....An understanding of the functional connection between the jaw muscles and various receptor organs in and around the mouth is necessary to elucidate the process of chewing and its underlying rules. Unless the details of this functional connection in health and disease are thoroughly understood, the diagnosis and treatment of chewing related disorders will remain at the present state. For example: a We still do not know why chewing in edentulous subjects is less efficient and why the bite forces in these individuals immediately fall to about 20 % of the teethed value. Do jaw muscles in these subjects get weak because they get less support from the receptor organs around the teeth? a We still do not understand the cause-causes of the temporomandibular dysfunction (a painful disease involving jaw muscles) which forms 18.7 % of total dental patients consulted per week in South Australia. This South Australian study indicated that the current treatments (such as pain killers, night plates, massage) Ocures? only about the half of all patients. We cannot increase the success of the treatment if we do not fully understand the control mechanisms of chewing? It is expected that the results of this study will establish the functional connection between one of the most important receptor organs in the mouth (periodontal mechanoreceptors) to the jaw muscle motoneurons in subjects with healthy teeth and gums and will illustrate the importance of keeping the periodontium healthy for developing strong and smooth masticatory forces. This knowledge can also allow us to treat jaw related disorders by approaches that bring back normal operation of the system. For example, this knowledge may help us design active dentures that replace the missing support.Read moreRead less