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Tinnitus is one of the most common types of disability for military personnel. Tinnitus also affects roughly 10% of the general adult population, nearly 25 million Americans. It is a serious problem for military service members and veterans. In 2015, tinnitus was diagnosed in over 150,000 veterans and was cause for disability benefits in almost 1.5 million veterans. Together, hearing loss and tinnitus represents one of the most common types of disability for military personnel. Compensation for veterans specifically with tinnitus approached $190 million in 2003. The objective of this project is to develop an electrophysiological test for tinnitus based on a newly discovered neural response to sound in the central auditory system, a long-lasting sound-evoked afterdischarge. Tinnitus is the sensation of ringing in the ears in the absence of a corresponding, physical sound. It is a symptom of a pathological response of the auditory system. Unfortunately, the underlying cause of tinnitus is not known, and there is no objective electrophysiological test for tinnitus. The sound-evoked afterdischarge behavior in the auditory system is an activity in the brain that continues after the end of a very long duration sound. In auditory brainstem responses, we have found that the amplitude of the evoked potentials in the brainstem is larger immediately after a long-duration sound than before the sound. This suggests that the brainstem response reflects the time-course of the afterdischarge behavior in single neurons. The main idea being tested in these experiments is that in tinnitus, the afterdischarge behavior becomes continuous, and this would eliminate any difference in the amplitude of the response before and after a long-duration sound. This project will investigate how the afterdischarge activity in the brain is changed with tinnitus. The results from the animal studies will be used to investigate the brain activity potentially related to tinnitus in human subjects with and without tinnitus. The ultimate goal is to develop an objective electrophysiological test for tinnitus that can be used clinically for both military and civilian patients. The methods produced here will benefit research world-wide on tinnitus. The electrophysiological tests developed in this project may be used in both military and civilian clinics to test for tinnitus. Because they only require subjects to listen to sounds at moderate levels while they sit quietly and recording takes place, there is little risk involved. Since the tinnitus diagnosis largely relies on self-reporting by the patient, these tests can screen for tinnitus objectively regardless of the report of the patient. Such tests would verify that patients receiving benefits for tinnitus actually have tinnitus. These tests may show that a normal type of brain activity is modified in tinnitus. If so, it will point to the biological mechanisms that are responsible for tinnitus and speed in its cure. A test developed in this project will allow the condition to be screened objectively as a part of the diagnosis and treatment of hearing and balance disorders.
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