Brain Imaging of Tinnitus

Overview

This study will use magnetic resonance imaging (MRI) to compare brain function in three groups of people: hearing-impaired people with tinnitus; hearing-impaired people without tinnitus; and people with normal hearing and without tinnitus. Also known as "ringing in the ears," tinnitus is the false sensation of sounds. Adults between 30 and 65 years of age who meet the following criteria may be eligible for this study: * Mild to moderate hearing loss who have experienced tinnitus daily for at least 1 year * Mild to moderate hearing loss who have never or rarely experienced tinnitus * Normal hearing who have never or rarely experienced tinnitus Candidates are screened with a medical history and questionnaires. Participants have a detailed hearing test to measure hearing and the nature of tinnitus. In a second visit, subjects have a brief physical examination, followed by MRI scanning. MRI uses a magnetic field and radio waves to produce images of body tissues and organs. For this procedure, the subject lies on a table that can slide in and out of the scanner (a narrow cylinder), wearing earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. The subject may be asked to lie still for up to 8 minutes at a time. During the MRI, the subject performs computer-based tasks that involve listening to sounds. Another hearing test is done after the MRI.

Subjective tinnitus, the false perception of sound in the absence of an acoustic stimulus, occurs frequently as a consequence of noise-induced deafness. The purpose of this study is to investigate the brain sites and mechanisms underlying tinnitus using a combined mathematical modeling and functional brain imaging experimental approach. Although studies have focused on the neural bases of tinnitus, it is not known why tinnitus arises only in certain cases of hearing loss, and the contribution of different brain regions in tinnitus perception is poorly understood. This in turn, prevents the development of better studies and new treatment methods for tinnitus. The primary hypothesis is that a network of brain regions, from auditory processing areas to emotional processing areas, contributes to, and modulates, tinnitus perception. The brain imaging study will be used to study differences in the network of brain regions involved in listening and discriminating sounds for tinnitus sufferers as compared to a control group of subjects with similar hearing loss but without tinnitus. This comparison should permit the identification of brain regions most active in tinnitus. An age matched control group without hearing loss and tinnitus will be included to determine those effects due to hearing loss alone. The mathematical computational modeling will use a previously developed large-scale neural network model of auditory processing in the cerebral cortex, which will be modified to induce tinnitus via different neural mechanisms. The modeling study should allow us to evaluate the contribution of different cortical regions and mechanisms to tinnitus perception; some changes in the model will be more successful than others in inducing tinnitus and in matching simulated brain imaging data with experimental brain imaging data. The modeling study will use the same stimuli and experimental paradigm as the functional brain imaging study. Comparing the experimental and modeling results will provide hypotheses about the most likely mechanism mediating tinnitus. Together, the modeling and experimental studies will advance our knowledge of the brain regions and mechanisms underlying tinnitus.