often permanently by up to 15 % of the population. In 1-2% of the general population the tinnitus sensation (typically a continuous high frequently hiss) is sufficiently loud to affect the quality of life and induce psychiatric distress including a risk of suicide. Although tinnitus can be induced by drugs or otological disease, most cases are associated with hearing loss consequent on noise exposure or the aging process. The incidence of tinnitus is likely to be increasing in our society among more youthful populations as well as in older people owing to noise exposure in our electronis and industrial age. The personal, social and public health costs of tinnitus are compounded by the fact that at present there are no effective medical treatments.pRecently, neuroscience research has begun to provide insight into the important question of how tinnitus is generated when hearing loss occurs. These insights have been coming from two complementary fields, (1) studies using animal models of hearing loss and (2) research on neural plasticity in the human brain. In this project, we propose to assemble an interdisciplinary team of Canadian and German scientists with established research accomplishments in these two fields to lead a neuroscience attack on the problem of tinnitus. Foundation studies conducted by members of our group increasingly suggest that tinnitus is the consequence of a cortical reorganization that occurs when the auditory cortex is deprived of its normal input by damage to the hearing organ. In this respect our findings support a parallel between the sensation of tinnitus and phantom limb sensations that are experienced by amputees. If we can understand how tinnitus develops when auditory input to the brain is altered by hearing injury, we may be able to design effective treatment procedures for existiing cases of tinnitus and prevent the development of tinnitus in individuals who have already experienced partial hearing impairments. Study of tinnitus will also provide insight into fundamental processes by which the brain reorganizes when deprived of its sensory input and into the brain processes that underlie the sensation of sound. These processes may be ubiquitous in the normal brain and provide the means by which the brain adapts to its dynamic sensory world.
