Important advances in our understanding of tinnitus

Neuroscientists working in the US and Europe have been using advanced brain imaging techniques to gain new insights into the parts of the brain involved not only in the generation of tinnitus but also the emotional reactions to it.

For some time neuroscience researchers interested in tinnitus have been aware that tinnitus, and importantly the sufferers' responses to it, can be modulated by stress and lack of sleep. This in turn has stimulated researchers to consider investigating parts of the brain not directly involved in processing sound. These are often referred to as non-auditory brain areas.

In one such study both auditory and non-auditory areas of the brain were investigated using functional magnetic resonance imaging, a technique often used in hospitals to assist in locating diseased or damaged parts of the body. With advanced software, first developed at the Institute of Neurology in London, they were able to measure changes in volume in specific areas that were considered to be related to changes in levels of neural activity.

The researchers led by Dr Mark M�hlau of the Technical University of Munich and Dr Josef. Rauschecker form Georgetown University Washington DC, used twenty eight control volunteers with no tinnitus and 26 volunteers with tinnitus. Importantly, the tinnitus volunteers had no serious hearing loss or history of noise damage to their ears. This meant any changes seen were not likely to be due to any loss in hearing but the presence of tinnitus.

In summary, they found that there were increases in the volume of a specific part of the so-called auditory system. In contrast there was a decrease in the volume of the non-auditory area. This was taken as evidence by the scientists that there had been changes in the structural organisation of the brain due to the tinnitus - an important finding in itself. The researchers postulated that these changes in the non-auditory area may in turn, be related with the emotional or subjective response of the tinnitus sufferers to their tinnitus.

This important finding is now stimulating the researchers to think about how this might inform the future use of drug therapies for patients with these types of changes. This is because the types of neurotransmitter used by the brain have been identified in these areas. The researchers now plan to see if this kind of study can be extended to patients whilst they experience differences in the levels of their tinnitus from 'completely absent' to 'severe'. This would then enable a better understanding of the precise involvement of these areas in individual tinnitus patients.