Project 1

The Neural Basis of Phantom Sounds (Tinnitus)

Tinnitus, defined as the presence of an auditory sensation without externally-delivered acoustic stimulation, is a very common problem in humans. It has been estimated that between 6-20% of the population suffer from chronic, persistent tinnitus with about 25% of these experiencing tinnitus that is so severe that it has a major impact on quality of life. Our understanding of the basic physiological mechanisms responsible for tinnitus and therefore the basis for treatments is still at an early stage. We have recently developed a simple animal model of tinnitus in which prior exposure to a loud sound that causes partial deafness, results in markedly raised action potential discharge rates in neurons in the auditory midbrain. So far we have only measured this central neural “tinnitus” after 3 weeks recovery from the initiating loud sound exposure, but it is of great interest to know the time course over which this abnormal central activity develops and what the relationship is to the time course of changes in peripheral (cochlear) sensitivity. In this project we will use groups of experimental animals at different time points after exposure, measure the changes in cochlear sensitivity using gross electrical recordings and record the firing rates of single neurons in the auditory midbrain of the same animals, using metal microelectrodes. The results will provide information that will help differentiate between central and peripheral sites of origin of tinnitus.