Working with long-time collaborators in Iowa, at the Human Brain Research Laboratory, we were able to take a rare opportunity to make direct and extensive recordings from the brain of a patient with tinnitus undergoing a neurosurgical procedure. By comparing states of higher and lower tinnitus loudness, we were able to 'map out' the tinnitus in his brain in an unprecedented level of detail.
In this study, run in collaboration with the Wellcome Trust Centre for Neuroimaging in London, we measured electromagnetic brainwaves while using sounds to trigger brief periods of increased (residual excitation) or decreased (residual inhibition) tinnitus loudness. By contrasting these brain states, we were able to map out brain activity corresponding to tinnitus within each individual volunteer.
We found surprising results, which showed that there was no single pattern of brain activity corresponding to tinnitus across all individuals or all conditions, but instead a complicated relationship that did not fit with any existing theories of how tinnitus is generated. This has led us to generate a new theory of tinnitus and explore previously untested research directions.
In this study, conducted at the Newcastle Magnetic Resonance Centre, we used a special type of MRI scans to measure the levels of key brain chemicals in the hearing parts of the brain in people with tinnitus and control volunteers matched for age, sex and hearing status. We found a decrease in a chemical called GABA associated with tinnitus, which may indicate a reduced ability to suppress brain activity in this area.
In this article, we bring together a large number of existing research findings, and several of our own results, in order to propose an account of how tinnitus actually develops in the brain, including further avenues for research to improve our understanding of the mechanisms of tinnitus and produce more effective treatments.