Changes in the brain activity of tinnitus patients may point to more effective treatment

Repetitive transcranial magnetic stimulation, known as rTMS, is a technique that has been tested as a treatment for tinnitus over the past couple of years.

During rTMS a stimulating coil is placed over the patient's scalp and an electric current is rapidly switched on and off. This creates a weak magnetic field that reaches up to 2cm into the top layers of the brain, causing changes to the electrical activity of neurons.

Still in the experimental stages, the treatment is thought to work by inhibiting the tinnitus signal and has been most effective at suppressing tinnitus when applied over the left temporal lobe of the brain. However, clinical trials have shown that the treatment is more effective in people who have had tinnitus for less than four years. New research at the University of Konstanz and University of Regensburg in Germany may shed light on why the treatment is less effective for longer-term tinnitus sufferers.

Dr Winfried Schlee and colleagues tested 21 patients with chronic tinnitus and 20 control participants using magnetoencephalography (MEG), which records the magnetic field produced by the electrical activity of the brain. The researchers aimed to find out whether there was a measurable difference between patients and controls in the activity of brain networks involving different regions.

Results showed a clear difference between tinnitus patients and controls in two parts of the MEG signal known as the alpha and gamma bands. Tinnitus patients showed a decrease in alpha band activity and an increase in the gamma band, whereas the controls showed the opposite, with alpha increased and gamma decreased. This supports other experiments that have found changes to the activity of brain networks in tinnitus patients.

Interestingly, differences were found within the tinnitus patient group between those whose tinnitus had lasted less than four years compared to those with more than four years tinnitus duration. The shorter duration group showed marked changes in MEG activity over the temporal region (which is home to the auditory cortex) on the left side. However the longer duration group showed changes across a more widespread network of brain areas.

“This is intriguing because rTMS is usually applied to the left temporal cortex in clinical trials and is only effective for patients with tinnitus of up to 3 or 4 years” said Dr Schlee. “Our experiment shows a major hub of activity in the left temporal cortex of patients with short tinnitus duration, so rTMS stimulation of this region could potentially have a great impact. However, since the gamma activity is more widespread in patients with a long history of tinnitus, the impact of stimulation to the left hemisphere is largely reduced.”

The results suggest that rTMS treatment targeting the left temporal lobe should be started shortly after tinnitus onset. For long-term sufferers a different approach is needed with the aim of changing a widespread cortical tinnitus network.